key: cord-0809819-l8s4dm0c
authors: Zmitek, K.; Hribar, M.; Lavrisa, Z.; Hristov, H.; Kusar, A.; Pravst, I.
title: Socio-demographic and knowledge-related determinants of vitamin D supplementation in the context of the COVID-19 pandemic: assessment of an educational intervention
date: 2021-04-23
journal: nan
DOI: 10.1101/2021.04.21.21255553
sha: 155e6af0f52638c99a44a8e8d516bcdc300d30ee
doc_id: 809819
cord_uid: l8s4dm0c

Vitamin D is a pro-hormone, essential for musculo-skeletal health, normal immune system, and numerous other body functions. Vitamin D deficiency is considered a risk factor in many conditions, and there is growing evidence of its potential role in the severity of COVID-19 outcomes. However, an alarmingly high prevalence of vitamin D deficiency is reported in many regions, and vitamin D supplementation is commonly recommended, particularly during wintertime. To reduce the risk for vitamin D deficiency in the Slovenian population during the COVID-19 pandemic, we conducted mass media intervention with an educational campaign. The objective of this study was to investigate vitamin D supplementation practices in Slovenia before and during the COVID-19 pandemic, and to determine the effects of the educational intervention on supplementation practices. Two data collections were conducted using an online panel with quota sampling for age, sex, and geographical location. A pre-intervention (N=602, April 2020) and post-intervention (N=606) sampling were done during the first and second COVID-19 lockdown, respectively. We also focused on the identification of different factors connected to vitamin D supplementation, with a particular emphasis on vitamin D-related knowledge. Study results showed significant changes in vitamin D supplementation in the population. Penetration of the supplementation increased from 33% in April to 56% in December 2020. The median daily vitamin D intake in supplement users was 25 {micro}g, with about 95% of supplement users taking safe intake levels below 100 {micro}g/daily. Vitamin D-related knowledge (particularly about dietary sources of vitamin D, the health-related impact of vitamin D, and the prevalence of deficiency) was identified as a key independent predictor of vitamin D supplementation. Based on the study findings, we prepared recommendations, which will enable the development of effective awareness campaigns for increasing supplementation of vitamin D.

Vitamin D is a pro-hormone, essential for musculo-skeletal health, normal immune system, and 14 numerous other body functions. Vitamin D deficiency is considered a risk factor in many conditions, 15 and there is growing evidence of its potential role in the severity of COVID-19 outcomes. However, 16 an alarmingly high prevalence of vitamin D deficiency is reported in many regions, and vitamin D 17 supplementation is commonly recommended, particularly during wintertime. To reduce the risk for 18 vitamin D deficiency in the Slovenian population during the COVID-19 pandemic, we conducted mass 19 media intervention with an educational campaign. The objective of this study was to investigate 20 vitamin D supplementation practices in Slovenia before and during the COVID-19 pandemic, and to 21 determine the effects of the educational intervention on supplementation practices. Two data 22

collections were conducted using an online panel with quota sampling for age, sex, and geographical 23 location. A pre-intervention (N=602, April 2020) and post-intervention (N=606) sampling were done 24 during the first and second COVID-19 lockdown, respectively. We also focused on the identification 25 of different factors connected to vitamin D supplementation, with a particular emphasis on vitamin D-26 related knowledge. Study results showed significant changes in vitamin D supplementation in the 27 population. Penetration of the supplementation increased from 33% in April to 56% in December 2020. 28

The median daily vitamin D intake in supplement users was 25 µg, with about 95% of supplement 29 users taking safe intake levels below 100 µg/daily. Vitamin D-related knowledge (particularly about 30 dietary sources of vitamin D, the health-related impact of vitamin D, and the prevalence of deficiency) 31 was identified as a key independent predictor of vitamin D supplementation. Based on the study 32 findings, we prepared recommendations, which will enable the development of effective awareness 33 campaigns for increasing supplementation of vitamin D. 34

Vitamin D is a pro-hormone, essential for musculo-skeletal health, normal immune system, and many 36 other body functions ( Hoffmann, & Marz, 2016). This micronutrient is also at the frontier of many debates about possible 38 dietary interventions during the COVID-19 pandemic, which has introduced unique threats to the 39 population and has challenged healthcare systems worldwide. 40

The worst COVID-19 outcomes and higher mortality rates are reported among immunocompromised 41 subjects, including older adults and malnourished people (Barazzoni et al., 2020) . Nutritional risks 42 have been identified as particularly relevant, highlighting the need for nutritional interventions (Liu, 43 Zhang available results are not yet fully conclusive (Koch, 2021) . While it is clear that well-controlled 53

intervention studies are needed in these areas, the high prevalence of vitamin D deficiency in many 54

populations is a rational cause for concernswith or without COVID-19 pandemic. Some countries 55 therefore updated their Vitamin D supplementation recommendations recently. In the UK for example, 56

revised governmental advice was issued in April 2020 (during the first COVID-19 lockdown), 57

recommending the use of vitamin D supplements for everyone during the autumn and winter months 58 (Koch, 2021) . According to additional UK guidance from December 2020, clinically vulnerable people 59 are now offered a free supply of daily vitamin D supplements for 4 months (UK, 2020). including Europe (Cashman et al., 2016) . Actually, across the northern hemisphere, at latitudes greater 71 than 40°N, the small amount of UVB in sunlight from October to March is insufficient to initiate 72 effective vitamin D synthesis. Therefore, substantial proportions of the European population rely on 73 dietary vitamin D and body stores to maintain a sufficient vitamin D status during the extended winter 74 season, and quite a high prevalence of vitamin D deficiency is reported in many countries worldwide 75 (Calvo, Physicians and the media were identified as key information providers on this topic, and it was 105 suggested that health professionals should also be better informed about the health effects of vitamin 106 D, and particularly about the vitamin D deficiency risk factors (Deschasaux et al., 2016) . Moreover, 107 the public should receive information that reflects the current knowledge on vitamin D health effects 108 and sources. This could contribute to improved vitamin D status in the population. 109

Vitamin D-related knowledge has not yet been systematically investigated in the Slovenian population, 110 but the high prevalence of vitamin D deficiency and building evidence about its role in COVID-19  111  have caused increased attention of mass media for this essential micronutrient, which could have  112 affected not only vitamin D-related knowledge, but also supplementation practices. Monthly frequency 113 of articles mentioning vitamin D in Slovenian mass media in the period 2019-2020 is presented in 114 Figure 1 . There are visible peaks in media coverage of vitamin D during the first COVID-19 lockdown 115

in March, and particularly in the last quartal of 2020. March 2020 peak corresponds with media 116 communication of physician D. Siuka (Siuka, 2020) , who proposed 10-steps in the fight against 117 COVID-19 (vitamin D supplementation was mentioned as one of the steps), another peak can be further 118 observed in October 2020, when vitamin D supplementation recommendations for physicians were 119 published on the web site of Slovenian endocrine society (Pfeifer, Siuka, Pravst, & Ihan, 2020), while 120 a major peak occurred in November, after an educational intervention. A press release (NUTRIS, 121 2020) was sent to major mass media channels, focused on recent results of the national Nutrihealth 122 study (Hribar et al., 2020) about the wide prevalence of vitamin D deficiency in the Slovenian 123 population. 124 

Considering these challenges, the objective of this study was to investigate individual vitamin D 136 supplementation practices in Slovenia before and during the COVID-19 pandemic and to determine 137 the effects of the abovementioned educational intervention on supplementation practices. Two data 138 collections were conducted: first during the first COVID-19 lockdown in April 2020, and second 139 during the second COVID-19 lockdown in December 2020after an educational intervention. We 140

were focused on the identification of different factors connected to vitamin D supplementation, with a 141 particular emphasis on vitamin D-related personal knowledge. In the absence of mandatory food 142 fortification and vitamin D supplementation, the identification of key knowledge gaps in the population 143 is essential for the preparation of efficient and educational public health campaigns for reducing 144 vitamin D deficiency. Identified knowledge gaps were already used for the educational intervention, 145

which was evaluated with sampling in December 2020. 146

This study was conducted in Slovenia. Sampling was done using an online panel survey in two periods. 149

Frist (pre-intervention) sampling period was between 22nd and 27th April 2020, during the first 150 COVID-19 lockdown, while the second (post-intervention) sampling (N=606) was between 11th and 151 30th December 2020, during the second COVID-19 lockdown. Educational intervention (press release 152 to mass media) was done between both collections, on 2nd November 2020 (details provided in Section 153 3.4). The survey was conducted in the Slovenian language as an amendment to the international Food-154 COVID-19 survey. Participants provided their informed consent to participate using an online form. 155

Ethical approval for the study was obtained from the Bioethical Committee of the Higher School of 156

Applied Sciences in Ljubljana, Slovenia (VIST ET-6/2020). 157 (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. analyses, these categories were joined into three larger education categories-lower (primary school), 178 medium (vocational school or high school), and higher (beyond high school). Self-reported financial 179 status was also measured (Very below average; Below average; Average; Above average; Very above 180 average). For statistical analyses, respondents were then classified into three categories: the below 181 average income category (includes respondents indicating very below and below average financial 182 status); the average group (indicates average financial status); and the above average category 183 (indicates above and very above average self-reported financial status). Respondents also reported the 184 size of their household, which was classified into three categories: household with children, single 185 person household, household with 2+ adults without children living together. Health condition was 186 also defined by three categories. The first included those with very low-and low health condition, the 187 second included respondents with average health condition and the third included participants 188 indicating high and very high self-reported health condition. Moreover, participants were asked to 189 report if they were supplementing their diet with vitamin D (a) before and (b) during the COVID-19 190

pandemic. If supplementation was reported, the participant was asked to provide the dosage of vitamin 191 D taken in as much detail as possible in order to enable a calculation of individual daily vitamin D 192

dosage. Questions were also asked about the extent to which their household had been afflicted with 193 COVID-19 using three questions that asked about infection, isolation or quarantine, and hospitalized 194 members. For the purpose of the analysis, these categories were further joined by one variable with 195 two levels. The participants who responded positively to any of the three questions were classified in 196 the "COVID-19 afflicted households" group, and the remaining respondents in the "COVID-19 not 197

afflicted households" group. The following three questions measured respondents' perceived risk in 198 relation to the disease: (1) the likelihood of any member of your household becoming infected by the 199 virus;

(2) the likely severity of the virus for any member of your household; and (3) the level of your 200 anxiety concerning the potential impact of the virus on your household. Participants were asked to 201 score these on a scale from 1 (very low) to 5 (very high). 202 All rights reserved. No reuse allowed without permission.

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Vitamin D-related knowledge was measured using an online tool, developed and described in detail by 204 Boland 800 IU IU/20 µg were considered as correct in our survey, because of the differences between regional 219

and EU-level recommendations (EFSA, 2016; GNS, 2012) 220

The vitamin D-related knowledge questionnaire used is provided in the Supplementary Information. 221

Six questions were used to assess all six of the above-mentioned dimensions of vitamin D-related 222 knowledge, and each question contributed equally to the calculation of the total knowledge score. 223

Every knowledge question was worth 1 point, producing a maximum score of 6 points. Single questions 224

were scored with 1 if the answer was correct, and 0 if the answer was incorrect. For multiple choice 225 questions, each correct response accounted for a fraction of the overall question. For instance, if a 226 question had 5 correct answers, each contributed 0.2 points. When calculating the total score, the sum 227 of correct responses was deducted from the sum of incorrect responses multiplied by the fraction parts. 228

In this way, a penalty for guessing was implemented to prevent participants from scoring maximum by 229 selecting all possible responses as correct. For this reason, the response "don't know" was not penalized 230 within the knowledge score. Penalization only occurred within a specific question. In cases where 231 negative scores were given, the whole question was scored as zero. 232

Results of pre-intervention data collection in April 2020 were used to identify vitamin D-related 234 knowledge dimensions, connected with vitamin D supplementation practices. Population-based 235 educational intervention started with the launch of a press release on November 2 nd 2020, which was 236 sent to e-mail addresses of major Slovenian media channels. The press release was focused on the 237 wide prevalence of vitamin D deficiency in the Slovenian population (NUTRIS, 2020). Intervention 238 resulted in several interviews and numerous publications in mass media. For example, in the last quartal 239 (Q4) of 2020 there were more vitamin D-related publications (N=911) in mass media, than together in 240

the whole year 2019 (N=786) (Figure 1) . 241

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(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. to investigate the predictors of knowledge and supplementation with vitamin D and to determine 247 differences between different sub-populations in terms of knowledge and supplementation. The 248

estimates of vitamin D-related knowledge were determined using age, sex, place of living, education, 249 financial status, health status, and employment, while the estimates of supplementation with vitamin 250 D were determined with respect to age, sex, place of living, education, financial status, and health 251 status. Additionally, a multivariable logistic regression analysis was used to investigate predictors of 252 an increase in vitamin D-related knowledge (December vs. April scoring). In this regard the analyses 253

were conducted using a subsample of subjects, which participated in both pre-intervention (April 2020) 254

and post-intervention (December 2020) data collection, with the exploitation of previously mentioned 255 socio-demographic determinants (age, sex, place of living, education, financial and health status). 256

Multivariable logistic regression analysis was also used to investigate the influence of different 257 dimensions of vitamin D-related knowledge on supplementation with vitamin D, separately for first 258 (April 2020) and second (December 2020) COVID-19 lockdown. For the purpose of binomial 259 regression analysis, respondents were classified into two categories: respondents taking and not taking 260

vitamin D supplements. The model parameters were estimated by the maximum likelihood method. 261

Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. A two-tailed z-test for 262

proportions was used to identify significant changes between the pre-and post-intervention 263 supplementation practices. In addition, a t-test for independent samples was used to test the difference 264 in overall vitamin D-related knowledge in pre-and post-intervention sample. Differences were 265 considered significant at p < 0.05. 266

Results 267

Socio-demographic and other characteristics of the participants are presented in Table 1. The  269 compositions of the pre-intervention (April 2020; N=602), the post-intervention (December 2020; 270 N=606), and the combined sample (April and December 2020; N=835) study samples are close to the 271 distribution in the population. Both sex and age distribution are quite comparable, with age groups 19-272 35 and 36-49 slightly over-represented, while the 50+ age group is somewhat under-represented. 273

Regarding educational level, the sample is under-represented for the lower education group. 274

Nevertheless, as the study was done as an online survey, such data could not be considered 275

representative, because the population who do not have access to the internet cannot be included. 276

The results in Table 1 reveal that about 9% of participants were somehow affected by COVID-19 in 277

April 2020, while the mean COVID-19 risk perception scores were below medium (3). While the 278 proportion of participants from COVID-19-affected households was much higher in December (25%), 279 all mean risk perception scores (rated from 1-very low to 5-very high) were still below scale medium 280

(3). In April the mean score for the likelihood of a household member becoming infected with the virus 281

(2.2 ±0.9) was lower in comparison with the score for the likely severity of the virus for household 282 members, and the score for the level of anxiety concerning the potential impact of the virus on the 283 household (2.6 ±1.2 and 2.7 ±1.1, respectively). This changed in December, when we observed 284 significant increase (p<0.001) in the reported likelihood of a household member becoming infected 285 with the virus in comparison with April (score 2.7 vs. 2.2, respectively). We should also note that 286 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 23, 2021. 

The results of the measurements of vitamin D-related knowledge are presented in Table 2 and Figure  294 2. The maximum vitamin D-related knowledge score would be 6, but in the April 2020 pre-intervention 295 study the highest observed score in our survey was 3.73, with a mean score of only 1.60 (95% CI: 296

1.53-1.67). The specific dimensions of the vitamin D knowledge provide even more interesting results. 297

Mean scores for dietary vitamin D sources (Q1) and vitamin D's health impact (Q2) were 0.26 (95% 298 CI: 0.25-0.28), while mean scores for factors affecting the biosynthesis of vitamin D (Q5) were 299 somewhat lower (0.23; 95% CI: 0.21-0.24). The majority of the respondents (54.5%) were aware that 300 the prevalence of vitamin D is above 20%, while the proportion of participants (Q3) knowing their 301 recommended daily intake of vitamin D (15-20 µg) and (Q4) the necessary sun exposure for an average 302 fair-skinned person, when legs and arms are exposed (10-60 minutes per week), was 10% and 28%, 303

respectively. 304

December 2020 measurements after conduction of educational intervention showed a statistically 305 significant increase in vitamin-D related knowledge scores (p<0.001). Mean total score significantly 306

increased for 38% -to score 2.21 (95% CI: 2.12-2.90). Notable differences were also observed in 307 specific dimensions of the vitamin D knowledge ( other vitamin D-related knowledge were much less pronounced. As can be observed from knowledge 313 distribution histograms in Figure 2 , the educational intervention resulted in increase in knowledge on 314 the tail of the distribution, with the population with poor pre-intervention vitamin D-related knowledge 315

having most notable knowledge increase after the intervention. 316 December 2020) vitamin D-related knowledge in the study sample. The horizontal (x) scale uses the 323 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. To provide further insights, linear regression analyses were used to determine adjusted means of 331 vitamin D-related knowledge, considering various socio-demographic and other factorsnamely age, 332 sex, place of living, education, financial status, health, and employment status. Analyses were done 333 separately for pre-intervention (April 2020) and post-intervention (December 2020) sample (Table 3) . 334

The pre-intervention analysis shows that age (F=4. 

Intervention-related changes were additionally investigated using a sample of subjects, for which we 355 had available two measurements of vitamin D-related knowledge. These were N=373 subjects, who 356 collaborated in both pre-intervention (April 2020) and post-intervention (December 2020) surveys. We 357 investigated predictors of an increase in vitamin D-related knowledge using multivariable logistic 358 regression analysis, focusing on age, sex, place of living, education, financial, and health status (Table  359 4). Altogether, 74% (N=274) of subjects had increased vitamin D-related knowledge scores in 360

December, in comparison with their April 2020 knowledge scoring. Education of the respondents have 361

shown to be the only significant (p<0.01) predictor of increased knowledge score. Those with medium 362 and higher education level have higher chances to increase their vitamin D-related knowledge with 363 intervention, in comparison to those with lower education level (OR 5.36, 6.34 vs. 1.00, respectively). 364 365 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 

The penetration of the pre-COVID-19 vitamin D supplementation was 33.7%, and very similar also in 376 the early stage of the COVID-19 pandemic in April 2020 (33.2%). Among those participants who 377

reported the amount of vitamin D supplementation they took before the COVID-19 pandemic or during 378 the pandemic in April, 58% did not report any change in their vitamin D supplementation practice, 379

while (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. To provide further insights into the connection between vitamin D supplementation practices and 418 vitamin D-related knowledge, we used a modeling approach based on the logistic regression method 419 (Figure 3) . Two models were constructed to investigate the probability of vitamin D supplementation, 420 using all six investigated dimensions of vitamin D-related knowledge. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 23, 2021. ; https://doi.org/10.1101/2021.04.21.21255553 doi: medRxiv preprint deficiency (about 80%) in adults between the beginning of October and the end of April (extended 473 wintertime), but the study design did not allow insights into the seasonal use of food supplements to 474 be captured. 475

In April 2020, about one-third of our study sample reported extended wintertime vitamin D 476 supplementation, and we did not observe considerable differences before and during the COVID-19 477 pandemic (33.7% vs. 33.2%, respectively). The observed greater penetration of vitamin D 478

supplementation, in comparison with Si.Menu/Nutrihealth 2017/2018 data, can be partially explained 479 by the fact that our measurements were done during the extended winter period when vitamin D 480

supplementation is usually advised. Although at that time there were no official policy 481 recommendations for vitamin D supplementation in the general population in Slovenia, this topic was 482 addressed by the mass media in March 2020 (Figure 1) , and greater penetration of the supplementation 483 was expected during COVID-19 lockdown in April 2020. At that time some mass media reports were 484

published (Siuka, 2020) 2020 this was the case in 25% of subjects (Table 1) . Furthermore, April 2020 mean score for the 495 reported likelihood of a household member becoming infected with the virus was notably lower (score 496 2.2/5) in comparison with December 2020 measurement (score 2.7/5). Also, the December 2020 survey 497 was conducted after the educational intervention. A press release (NUTRIS, 2020) about the wide 498 prevalence of vitamin D deficiency in the Slovenian population (Hribar et al., 2020) was sent to all 499 major mass media at the beginning of November 2020, which received a lot of media attention ( Figure  500 1). 501

Analyses of the December 2020 dataset showed that penetration of dietary supplementation with 502 vitamin D increased to 55.6% (from 33.7% in April), with the majority of supplement users taking a 503 daily dosage of at least 25 µg vitamin D. The proportion of subjects with very high vitamin D intakes 504

(above UL level of 100 µg/day (EFSA, 2012) increased during the pandemic, however about 95% of 505 those supplementing vitamin D were still within safe intake levels (<100 µg/day). Nevertheless, the 506 observation that, in some subjects, vitamin D intakes increased drastically during the pandemic 507 highlights the need for very careful communication of vitamin D supplementation practices in relation 508

to specific health-related events, such as the COVID-19 pandemic. 509

Vitamin D supplementation in the general population is likely to stay voluntarily in most countries. To 510 use dietary supplementation as a strategy for lowering the risk of vitamin deficiency in such 511 circumstances, very efficient public awareness programs would need to be implemented. In this study, 512

we therefore focused on the identification of predictors of vitamin D supplementation practices. In 513

April 2020 the most important predictors of vitamin D supplementation were the financial and health 514 status of the participants, and specific dimensions of individual vitamin D-related knowledge. 515

Multivariable logistic regression analysis highlighted the highest odd ratios for vitamin D 516 supplementation in participants with a lower health status and in those with a higher financial status. 517 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. In April 2020, only 33% of subjects used vitamin D supplements, while in the low health status group 518 this was the case in 52%, and in the below-average financial status group in 25%. This indicates that 519 the lowest supplementation rates were observed in those, who would probably need the 520 supplementation the most. These observations are in line with our expectations that wealthier persons 521 can more easily afford to purchase food supplements and that those with a lower self-reported health 522 status more commonly used supplements. Interestingly, we did not observe significant differences 523 between different sexes and age groups, although we would expect a higher penetration of 524 supplementation in older adults (where vitamin D deficiency is commonly more pronounced (Spiro & 525 Buttriss, 2014)), and in women, who are typically more frequent users of food supplements (Tariq et  526 al., 2020). But the situation changed after the educational intervention; in December 2020 dataset age 527 became the only strongly significant (P=0.01) parameter, with the highest supplementation rates in 528 elderly subjects (72%). It should be also noted, that 52% of participants in the lower financial status 529 group reported vitamin D supplementation. Study results indicate that we managed to considerably 530 increase vitamin D supplementation across different population groups, including in the most 531

vulnerable groups, such as the elderly population. supplementation. This was noted both in pre-and post-intervention surveys. The above-mentioned 555 observations are very important for the preparation of key messages that need to be well communicated 556

if we want to increase vitamin D supplementation in the general population. 557

Our study also provides interesting insights into the overall knowledge about vitamin D in the 558

Slovenian population. Knowledge was scored using a tool developed by Boland et al. (Boland et al., 559 2015) . The original questionnaire was tested on Canadian students; the results showed poor knowledge 560 and highlighted the need for more efficient health promotion programs. The reported mean total score 561 in the Canadian study was 29%, while in our case it was 27% (1.60/6) before the intervention, and 37% 562 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 23, 2021. ; https://doi.org/10.1101/2021.04.21.21255553 doi: medRxiv preprint (2.21/6) after the educational intervention. Knowledge about factors affecting vitamin D levels were 563 also comparably low both in the Canadian study and in our pre-intervention April 2020 study (23%), 564 but in our case this score increased to 45% after the educational intervention. On the other hand, in 565

April 2020 we observed notably lower scores for vitamin D health impact than in the Canadian study 566 (26% vs 37%, respectively), but this factor also notably improved after the intervention (40%). 567

Contrary, about a quarter of our participants (both in pre-and post-intervention survey) correctly 568

identified the amount of time in the sun required to produce adequate vitamin D (only 14% in the 569

Canadian study), while, in both studies, less than 10% identified the correct recommended vitamin D 570

intakes. It should be noted that other studies also identified serious vitamin D-related knowledge gaps 571

in various other populations. Deschasaux were aware of the bone health-related effects of vitamin D, and only 36% identified sunlight exposure 576 as a factor influencing vitamin D production. Interestingly, they also observed that those with more 577 knowledge about the health functions of vitamin D were more likely to use vitamin D supplements. 578 We should note, however, that there were considerable differences in the tools used for measuring 579 vitamin D-related knowledge in these studies. 580

The strength of this study is in the controlled sampling conducted in two short duration periods during 581 very early (April 2020) and late stage (December 2020) of the COVID-19 pandemic. While the use of 582 an online panel could be considered as a study limitation, we should mention that considering 583 pandemic-related restrictions, the use of an online study was the only option in practice. Both data 584 collections were done during national lockdowns when all schools and universities were closed, non-585 essential workplaces in the public sector were closed and the private sector was recommended to close 586 or restrict the number of people working; personal movement was restricted to within one's 587 municipality and operation of the public transport was limited. While food stores were open, non-588 essential stores were mostly closed. There was governmental advice in place to stay at home and to 589 limit contact with others, while gatherings in public places were limited. We should note that, for some 590 people, these circumstances might have limited the access of participants to vitamin D supplements 591 during the COVID-19 pandemic. The quota sampling approach enabled a fair balance between the 592 genders, age groups, and urban and rural areas. However, the approach used is also subject to 593

limitations. The requirements for computer/smartphone use and internet access denied the inclusion of 594 participants of the lowest socio-economic status. On the other hand, Slovenia has a very good internet 595 infrastructure, and most households use computers. According to data from the Slovenian Statistical 596

Office, more than 80% of the Slovenian population (16-74 years) is using internet (STAT, 2019). Also, 597

home-schooling was in place in Slovenia during COVID-19 lockdowns for all elementary/secondary 598 schools and universities, with online lectures. Nevertheless, the sampling approach may partially 599 explain the difficulties in achieving representativeness in the study samples in the terms of educational 600 level. 601

Another limitation is related to the vitamin D-related knowledge survey used. To provide some 602 international comparability, we used a tool that was previously tested on Canadian students (Boland et  603 al., 2015), but has not been validated or used in other subject groups. Despite the above-mentioned 604

limitations, the authors believe that the tool used provided reliable predictors of vitamin D 605 supplementation practices. We should also note that some of the study subjects participated both in 606

April and December 2020 data collections. While this strengthens our study, because enabled us to 607 investigate changes in the same subjects, such sampling could also present a limitation. Although study 608 All rights reserved. No reuse allowed without permission.

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The copyright holder for this preprint this version posted April 23, 2021. ; https://doi.org/10.1101/2021.04.21.21255553 doi: medRxiv preprint surveys were not conducted in a way to increase vitamin-D related knowledge or to affect vitamin D 609 supplementation practices in study participants, survey questions brought vitamin D topic under 610 attention. A series of control checks were therefore performed to verify, if this had any meaningful 611 effect on the reported study results. For example, we have compared mean vitamin-D knowledge scores 612 in the second survey (December 2020) between new subjects (N=233), and those that already 613 participated in April 2020 survey (N=373), but no significant differences were observed. Furthermore, 614

we compared December 2020 vitamin D supplementation prevalence in both these two groups. No 615 meaningful differences were observed; in both groups vitamin D supplementation rates were above 616 50%, and median daily vitamin D intake was 25 µ. Therefore, we believe that the reported results were 617 not majorly affected by exposing subjects to vitamin D topics. 618

Conclusions, policy, and research recommendations 619

While most foods are generally quite poor in vitamin D, they can assure adequate intake of this vitamin, 620 particularly in regions with efficient food fortification policies (Calvo et al., 2005) . However, in regions 621 without such policies, a considerable proportion of the population is at risk for insufficient vitamin D 622 status, which could be managed with supplementation. Findings of our study suggest that at beginning 623 of 2020 most of the Slovenian population did not supplement their diet with vitamin D, despite the fact 624 that previous studies indicated alarmingly high vitamin D deficiency prevalence between October and 625

April. While we did not observe notable changes in vitamin D supplementation practices early in the 626 COVID-19 pandemic (April 2020), in comparison to pre-COVID-19 observations, a very successful 627 educational campaign using mass media resulted in a major increase in frequency of winter-time 628

vitamin D supplementation. Pre-intervention study highlighted financial status as an independent 629

predictor of vitamin D supplementation, with those with a below average financial status having the 630 lowest proportion of vitamin D supplementation. This indicates that the financial dimensions of vitamin 631 D supplementation also need to be considered by policy makers to ensure the protection of vulnerable 632 groups. 633

Vitamin D-related knowledge was also found to be a key predictor of dietary supplementation, with 634 some knowledge dimensions being more important than others. The three key dimensions identified as 635 predictors of more likely vitamin D supplementation are knowledge about dietary sources of vitamin 636 D, the health-related impact of vitamin D, and the prevalence of vitamin D deficiency in the population. 637

Considering the study findings, the following key messages would need to be embedded into awareness 638 campaigns in order to increase supplementation with vitamin D: 639 (a) Vitamin D can be biosynthesized by human skin when we are sufficiently exposed to sunlight, 640 but such biosynthesis is efficient only between May and September. (Note: this is geolocation-641 related information reflecting the situation in Slovenia). 642 (b) In the absence of efficient biosynthesis, enough vitamin D needs to be provided by the diet. 643

However, only oily fish and a few other foods are notable natural dietary sources of vitamin D. 644

Therefore, the typical dietary intake of vitamin D with natural foods is much lower than 645 recommended intake for the normal functioning of the human body. 646 (c) Vitamin D has numerous health functions. It also contributes to the maintenance of normal 647 bones, muscle function, and the function of the immune system. 648

(d) In particular, between October and April, there is a very high prevalence of vitamin D 649 deficiency in the population. (Note: this is nationally specific information reflecting the 650 situation in Slovenia). 651 All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted April 23, 2021. ; https://doi.org/10.1101/2021.04.21.21255553 doi: medRxiv preprint

These key messages were constructed based on our preliminary results, using April 2020 sampling, 652 and used in the populational educational intervention in November 2020. Herein reported study results 653

showed that the intervention was very efficient, however long-term effects are yet to be determined in 654 future seasons. Additional studies are therefore needed in the future, preferably in a similar calendar 655 seasonduring the winter. If vitamin D supplementation practices will change in long term, 656 epidemiological data on vitamin D status in key population groups should be also revisited. It should 657 be noted that the above provided communication messages result from data collected in the Slovenian 658 population. While very similar messages might also be applicable in other regions, they should be 659 adapted to address regional and population differences. The efficiency of awareness campaigns should 660 be always carefully evaluated. 661

The raw data supporting the conclusions of this article will be made available by the authors, without 663 undue reservation. 664

Ethical approval for this study was obtained from the Bioethical Committee of the Higher School of 666

Applied Sciences in Ljubljana, Slovenia (VIST ET-6/2020). The survey was conducted in the 667

Slovenian language as an amendment of the international survey Food-COVID-19: Lifestyle and 668

dietary patterns, and nutrition knowledge. The participants provided their informed consent to 669 participate in this study via an online form. 670

We acknowledge the support of Nina Zupanič and Sanja Krušič (Nutrition Institute

Primož Logar and the team at 694 Marketagent reSEARCH GmbH (Baden, Austria) for the programming of the survey tool and the use 695 of their consumer panel in Slovenia. We also acknowledge the support of physicians in 696 communications with media and practitioners, particularly Marija Pfeifer, Darko Siuka, Barbara 697 Hrovatin

Providing nutritional support for the patient with COVID-19

Vitamin D and survival in COVID-19 patients: A quasi-experimental study

Vitamin D Supplementation Associated to Better Survival in Hospitalized Frail Elderly 707 COVID-19 Patients: The GERIA-COVID Quasi-Experimental Study

Vitamin D status and ill health: a systematic 710 review

ESPEN expert statements and practical guidance for nutritional management of 713 individuals with SARS-CoV-2 infection

A Basic Review of the Preliminary Evidence That COVID-19 Risk and Severity 716 Is Increased in Vitamin D Deficiency. Frontiers in Public Health

A survey of university students' vitamin D-related 719 knowledge

Early nutritional supplementation in non-critically ill patients hospitalized for the 2019 722 novel coronavirus disease (COVID-19): Rationale and feasibility of a shared pragmatic 723 protocol

Vitamin D intake: A global perspective of current 725 status

Vitamin D deficiency in Europe: pandemic?

What Do People Know and Believe about Vitamin D?

Scientific Opinion on the Tolerable Upper Intake Level of vitamin D

Dietary reference values for vitamin D

López 737

Effect of calcifediol treatment and 738 best available therapy versus best available therapy on intensive care unit admission and 739 mortality among patients hospitalized for COVID-19: A pilot randomized clinical study. The 740

Correspondence table for Local Administrative Units (LAU) -NUTS

Region-specific nutrient intake patterns exhibit a geographical gradient within and between 747 European countries

German Nutrition Society: New reference values for vitamin D

Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and 752 COVID-19 Infections and Deaths

A 754 systematic review of vitamin D status in populations worldwide

Evaluation, treatment, and prevention of vitamin D deficiency: an 758

Endocrine Society clinical practice guideline

Nutrihealth Study: Seasonal Variation in Vitamin D Status Among the Slovenian Adult and 762 Elderly Population

Institute of Medicine: Dietary Reference Intakes for Calcium and Vitamin D

Changes in food 766 consumption during the COVID-19 pandemic: analysis of consumer survey data from the first 767 lockdown period in Denmark, Germany and Slovenia. Frontiers in Nutrition

SARS-CoV-2 positivity 770 rates associated with circulating 25-hydroxyvitamin D levels

Vitamin D and COVID-19: why the controversy?

Vitamin D -has the new dawn for dietary 775 recommendations arrived?

Nutrition support in the time of SARS-CoV-2 777 (COVID-19)

Therapeutic 779 strategies for critically ill patients with COVID-19

Clinical significance of 782 nutritional risk screening for older adult patients with COVID-19

Vitamin D supplementation to prevent acute respiratory infections: individual 786 participant data meta-analysis

Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and 790 meta-analysis of individual participant data

Breast cancer risk markedly lower with serum 25-hydroxyvitamin D 794 concentrations ≥60 vs <20 ng/ml (150 vs 50 nmol/L): Pooled analysis of two randomized trials 795 and a prospective cohort

Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results

Low plasma 25(OH) vitamin D level is associated with increased risk 801 of COVID-19 infection: an Israeli population-based study

Jeseni in pozimi vitamina D primanjkuje kar 80% prebivalcem Slovenije (Engl. 804 translation: During autumn and winter 80% of the Slovenian population has not enough vitamin 805 D)

Knowledge, Attitudes and 808 Perceptions towards Vitamin D in a UK Adult Population: A Cross-Sectional Study

Seasonal Changes in Vitamin D-Effective UVB Availability in Europe 812 and Associations with Population Serum 25-Hydroxyvitamin D

Vitamin D Knowledge, Attitudes, and 815 Behaviors in Young Danish Women with a Non-Western Ethnic Minority Background-A 816 Questionnaire Survey

Priporočila za nadomeščanje vitamina D3 (Engl. 818 translation: Recommendations for suplementation with vitamin D)

Rationale and Plan for Vitamin D Food Fortification: A Review and Guidance Paper

Short term, high-dose vitamin D supplementation for COVID-19 disease: a randomised, 825 placebo-controlled, study (SHADE study)

Coronavirus disease COVID-19 in Slovenia

Zdravnik svetuje: 10

Use 836 of dietary supplements in the European Prospective Investigation into Cancer and Nutrition 837 calibration study

Vitamin D: An overview of vitamin D status and intake in Europe

Usage of internet in households and by individuals

Assessment of knowledge, attitudes and practice towards 843 Vitamin D among university students in Pakistan

Vitamin D and clinically extremely vulnerable (CEV) guidance

Dawson-849

A global representation of vitamin D status in healthy populations

Vitamin D in preventive medicine: are we ignoring the evidence? British 852

Vitamin D and airway infections: a 854 European perspective

No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity

The authors declare that this research was conducted in the absence of any commercial or financial 682 relationships that could be construed as potential conflicts of interest. The funders had no role in the 683 design of the study; in the collection, analyses, or interpretation of data; in the writing of the 684 manuscript; or in the decision to publish the results. We acknowledge that I.P. has led and participated 685in various other research projects in the areas of nutrition, public health, and food technology, which 686were (co)funded by the Slovenian Research Agency, Ministry of Health of the Republic of Slovenia, 687the Ministry of Agriculture, Forestry and Food of the Republic of Slovenia and, in cases of specific 688 applied research projects, also by food businesses. I.P. and K.Z. are members of a national workgroup 689