key: cord-0302986-vjymh8oc
authors: Richardson, T. G.; Power, G. M.; Davey Smith, G.
title: Associations between vitamin D and disease risk may be attributed to the confounding influence of adiposity during childhood and adulthood: a lifecourse Mendelian randomization study
date: 2022-05-16
journal: nan
DOI: 10.1101/2022.05.11.22274956
sha: 06340f8de4c6f6c9dbebac183f37fec50199a35c
doc_id: 302986
cord_uid: vjymh8oc

Background: Vitamin D supplements are widely prescribed to help reduce disease risk. However, this strategy is based on findings using conventional epidemiological methods which are prone to confounding and reverse causation. Methods: In this short report, we leveraged genetic variants which differentially influence body size during childhood and adulthood within a multivariable Mendelian randomization (MR) framework, allowing us to separate the genetically predicted effects of adiposity at these two timepoints in the lifecourse. Results: Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), there was strong evidence that higher childhood body size has a direct effect on lower vitamin D levels in early life (mean age: 9.9 years, range=8.9 to 11.5 years) after accounting for the effect of the adult body size genetic score (Beta=-0.32, 95% CI=-0.54 to -0.10, P=0.004). Conversely, we found evidence that the effect of childhood body size on vitamin D levels in midlife (mean age: 56.5 years, range=40 to 69 years) is putatively mediated along the causal pathway involving adulthood adiposity (Beta=-0.17, 95% CI=-0.21 to -0.13, P=4.6x10-17). Conclusions: Our findings have important clinical implications in terms of the causal influence of vitamin D deficiency on disease risk. Furthermore, they serve as a compelling proof of concept that the timepoints across the lifecourse at which exposures and outcomes are measured can meaningfully impact overall conclusions drawn by MR studies. Funding: This work was supported by the Integrative Epidemiology Unit which receives funding from the UK Medical Research Council and the University of Bristol (MC_UU_00011/1).

Associations between vitamin D deficiency and disease risk have been widely reported by 45 conventional epidemiological studies, including diseases which typically have a late-onset 46 over the lifecourse, such as coronary artery disease, but also those which may be diagnosed 47

in early life such as type 1 diabetes (T1D). As a result, vitamin D supplements are widely 48 prescribed with an estimated 18% of adults in the USA reportedly taking supplements daily 49 (Rooney et al., 2017) . However, there is increasing evidence from the literature suggesting 50 that vitamin D supplements may be ineffective at reducing disease risk in the population 51 (Murai et al., 2021) , and although there are notable exceptions (e.g. multiple sclerosis 52 (Mokry et al., 2015 , Vandebergh et al., 2022 ), this raises uncertainty into the causal effects 53 of vitamin D levels on many disease outcomes. Furthermore, these conventional 54 associational studies may have been susceptible to bias, given that vitamin D levels are 55 known to differ amongst individuals based on various lifestyle factors, including their body 56 mass index (BMI), as well as being prone to reverse causation, for example due to 57 inflammatory processes which are known to lower vitamin D levels ( 

In this study, we applied lifecourse MR to investigate the independent effects of childhood 81 and adult body size has a largely indirect influence on 25-hydroxyvitamin D (25OHD) levels 82 measured during childhood (mean age: 9.9 years, range=8.9 to 11.5 years) using the UKB study, evidence of an effect of higher childhood body size on adulthood measured 92 25OHD levels (Beta=-0.14, 95% CI=-0.10 to -0.03, P=2.4x10 -4 ) attenuated in a multivariate 93 setting upon accounting for adulthood body size (Beta=0.04, 95% CI=-0.01 to 0.08, P=0.10). 94

In contrast, strong evidence of an effect for higher adult body size on lower 25OHD levels 95 measured in adulthood was found in the multivariable model (Beta=-0.17, 95% CI=-0.21 to 96 -0.13, P=4.6x10 -17 ) ( Figure 1C ). This suggests that childhood body size has an indirect 97 influence of 25OHD levels in adulthood, likely due to its persistent effect throughout the 98 lifecourse ( Figure 1D) . 99 100 . CC-BY 4.0 International license It is made available under a 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 May 16, 2022. ; for all study participants. Ethical approval for this study was obtained from the ALSPAC 153

hydroxyvitamin D (25OHD) levels were obtained from non-fasting blood samples taken 155 from ALSPAC participants at mean age 9.9 years (range=8.9 to 11.5 years) which were log 156 transformed to ensure normality. 157 158 Derivation of genetic instruments for childhood and adulthood body size have been 159 described in detail previously . In brief, genome-wide association 160 studies (GWAS) were conducted on 463,005 UK Biobank (UKB) participants (mean age: 161 56.5 years, range=40 to 69 years) who had both reported their body size at age 10 as well 162 as had their BMI clinically measured. Genetic instruments were identified from these 163 analyses (based on P<5x10 -8 ) and the resulting genetic score for childhood body size has 164 been validated using measured childhood BMI in ALSPAC (Richardson et al., 2020) , the 165 Young Finns Study and the Trøndelag Health (HUNT) study 166 (Brandkvist et al., 2020) . Genetic estimates on adulthood 25OHD were obtained from a 167 previously conducted GWAS in UKB (Manousaki et al., 2020) . Despite having overlapping 168 samples when analysing our body size instruments against the adulthood measure of 169 . CC-BY 4.0 International license It is made available under a 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 May 16, 2022. ; https://doi.org/10.1101/2022.05.11.22274956 doi: medRxiv preprint vitamin D, there was little evidence of inflated type 1 error rates (based on the calculator at 170 https://sb452.shinyapps.io/overlap) . 171 172 Mendelian randomization (MR) analyses to estimate genetically predicted effects on 173 childhood 25OHD were conducted in a one-sample setting using individual level data from 174 ALSPAC after generating genetic risk scores for our body size instruments with adjustment 175 for age and sex. MR analyses to estimate effects on adulthood 25OHD were undertaken in a 176 two-sample setting using the inverse variance weighted (IVW) method (Burgess et al., 177 2013) , as this allowed us to additionally perform analyses using the weighted median and 178 MR-Egger methods (Bowden et al., 2015 , Bowden et al., 2016 . (Supplementary Table 1) . 179

Multivariable MR were performed in one-and two-sample settings respectively for CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 16, 2022. ;

Mendelian randomization with invalid 216 instruments: effect estimation and bias detection through Egger regression

Mendelian Randomization with Some Invalid Instruments Using a Weighted Median Estimator

Cohort Profile: the 'children of the 90s'--the index 223 offspring of the Avon Longitudinal Study of Parents and Children

Separating the genetics of childhood and adult 226 obesity: a validation study of genetic scores for body mass index in adolescence and adulthood in 227 the HUNT Study

Mendelian randomization analysis with 229 multiple genetic variants using summarized data

Bias due to participant overlap in two-231 sample Mendelian randomization

Mendelian randomization': can genetic epidemiology 233 contribute to understanding environmental determinants of disease?

Cohort Profile: the Avon Longitudinal Study of Parents and Children: ALSPAC mothers cohort

Intake of 239 vitamin D and risk of type 1 diabetes: a birth-cohort study

Vitamin D levels and risk of type 1 diabetes: A 242 Mendelian randomization study

Genome-wide Association 245 Study for Vitamin D Levels Reveals 69 Independent Loci

Vitamin D and Risk of Multiple 248 Sclerosis: A Mendelian Randomization Study

High Dose of Vitamin D3 on Hospital Length of Stay in Patients With Moderate to Severe 253 COVID-19: A Randomized Clinical Trial

Mendelian Randomization Analyses Suggest Childhood Body Size Indirectly Influences End 256

Points From Across the Cardiovascular Disease Spectrum Through Adult Body Size

Research digest: vitamin D supplementation

Childhood body size directly increases type 1 diabetes risk based on a 263 lifecourse Mendelian randomization approach

Evaluating the direct effects of 266 childhood adiposity on adult systemic metabolism: a multivariable Mendelian randomization 267 analysis

Use of 269 genetic variation to separate the effects of early and later life adiposity on disease risk: 270 mendelian randomisation study

Mendelian Randomization: Concepts and Scope. 272 Cold Spring Harb Perspect Med

274 Trends in Use of High-Dose Vitamin D Supplements Exceeding 1000 or 4000 International 275 Units Daily

An examination of 277 multivariable Mendelian randomization in the single-sample and two-sample summary data 278 settings

Environmental risk factors in 280 multiple sclerosis: bridging Mendelian randomization and observational studies

Hospitals Bristol NHS Foundation Trust and the University of Bristol. The views expressed 211 in this publication are those of the author(s) and not necessarily those of the NHS, the 212 National Institute for Health Research or the Department of Health. This publication is the 213 work of the authors and TGR will serve as guarantor for the contents of this paper. 214