key: cord-0889905-kclj0iw0
authors: Krittanawong, Chayakrit; Kumar, Anirudh; Wang, Zhen; Baber, Usman; Bhatt, Deepak L.
title: Self-employment and Cardiovascular Risk in the US General Population
date: 2020-06-11
journal: International Journal of Cardiology. Hypertension
DOI: 10.1016/j.ijchy.2020.100035
sha: 3ad110848fad714fa0858e766ede42b05161367f
doc_id: 889905
cord_uid: kclj0iw0

ABSTRACT Background Studies on self-employment and cardiovascular risk are very limited. We examined the relationship between self-employment and cardiovascular risk among the general population in the United States from 1999 to 2016. Methods Using the National Health and Nutrition Examination Survey (NHANES), we identified all patients with hypertension (HTN), hyperlipidemia (HLD), diabetes mellitus (DM), stroke, heart failure (HF), and coronary artery disease (CAD) between 1999 and 2016. Type of job was defined based on the participant’s response to the survey question as “an employee of a private company, business, or individual for wages, salary, or commission” or “self-employed in own business, professional practice or farm”. Multivariable logistic regression analyses were performed to adjust for confounders. Results Of 30,103 patients, 2,835 (9.4%) were self-employed in their own business, professional practice, or farm and 27,268 (90.6%) were employed by a private company, business, or government. After adjusting for age, race, sex, BMI, marital status, educational level, health insurance status, smoking status, sleep duration and lipid profiles, self-employed individuals had a higher prevalence of HTN (OR: 1.12; 95% confidence interval [CI] 1.05 - 1.20), HLD (OR: 1.10; 95% CI 1.07 - 1.31), stroke (OR: 1.45; 95% CI 1.27 - 1.67), HF (OR: 1.17; 95% CI 1.03 - 1.32), and CAD (OR: 1.26; 95% CI 1.13 - 1.35) (all P < 0.05). Conclusions Self-employment may be associated with greater cardiovascular risk in the US general population. Further prospective studies are urgently needed to establish the optimal preventive strategy to reduce cardiovascular risks in self-employed individuals.

Governments worldwide are trying to encourage self-employment to boost growth and enhance business to become a priority in contemporary economies. Studies have shown that selfemployment may lead to adversity and was associated with being prescribed anxiolytics. (1, 2) However, studies on self-employment and cardiovascular risk are very limited and inconsistent. (3) (4) (5) (6) Farmers, for example, tend to have less cardiovascular risk (5) than other occupational groups, while self-employed professionals have a greater observed all-cause mortality than employed professionals in the USA.(7) Financial instability, social isolation, unstable working schedule, operational issues, work-related stress, economic insecurity, and local policies could be mechanisms by which self-employment could lead to adverse cardiovascular outcomes, depending on the exact nature of the business.(8) Most importantly, occasional natural disasters (e.g., floods, hurricanes, tornadoes) or infectious disease outbreaks (e.g., COVID-19) may cause business interruption due to operational costs (e.g., inventory, event cancellation, rent, supply chain losses, exposure liabilities, or employee compensation). This study sought to investigate associations between self-employment and cardiovascular risk using the NHANES survey between 1999 and 2016.

The NHANES survey, a series of complex and multistage surveys of general health, employment characteristics, nutritional status, lifestyle factors, and laboratory values, was conducted by the Centers for Disease Control and Prevention (CDC) along with the National Center for Health Statistics (NCHS) (https://www.cdc.gov/nchs/nhanes/). Data from nine NHANES cohorts (1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, 2011-2012, 2013-2014, 2015-2016) were merged. All participants signed consent for participation, and the National Center for Health Statistics Research Ethics Review Board reviewed and approved the NHANES survey.

We compared differences amongst those who were self-employed in their own business, professional practice, or farm and those who were employed by a private company, business, or Table 1 ). The main question was used as the inclusion criteria for the study sample. Type of job was defined based on the participant's response to the survey question: 'Which of these best describes your job or work situation?' The participant's response as "an employee of a private company, business, or individual for wages, salary, or commission", "self-employed in own business, professional practice or farm" were included. Respondents who responded, "don't know" or "refused" for the question were excluded. We reported continuous variables as mean ± standard deviation. We performed multivariable logistic regression adjusting for age, race, sex, BMI, marital status, educational level, health insurance coverage, smoking status, sleep duration, and lipid profiles. R 3.4.0 and Stata version 14.2 were used for analyses.

A total of 30,103 patients who represented the total US civilian, non-institutionalized population of 299.3 million people between 1999 and 2016 were included: 2,835 (9.4%) were self-employed in their own business, professional practice, or farm, and 27,268 (90.6%) were employed by a private company, business, or government. Self-employed individuals were older, more likely to be male, had higher systolic, diastolic blood pressure, cholesterol, triglyceride, and LDL cholesterol levels than employed individuals (all p-values < 0.0001). Compared with employed individuals, those who were self-employed had a higher reported prevalence of DM, HTN, HLD, stroke, HF, and CAD (all p-values < 0.05). 

In the present study using a large-scale national survey, we found that self-employed individuals had a higher prevalence of cardiovascular risks, including HLD, HTN, stroke, HF, and CAD in the contemporary US population. Self-employed individuals may encounter adversity such as financial management (e.g., very low-profit margin, rent, lack of funding/line of credit, high customer acquisition cost), work-related stress, unstable working schedule (e.g., working on weekends, no time for annual physical, or routine doctor visits), operational problems (e.g., inability to control expenses or overexpansion), local policies, and a lack of essential health insurance, leading to cardiovascular risk. (1, (9) (10) (11) (12) (13) Studies have shown that, compared with employed individuals, self-employed individuals are likely to be dedicated, selfdetermined(14,15), have high workloads(16), a strong work-commitment (17) , low support(18), economic insecurity (19) , and be more motivated to engage with their work (20) , resulting in insufficient time and effort into their health (e.g., unhealthy diet and lifestyle). A previously published study showed that self-employed individuals, particularly those with small business owners, were probably exposed to socioeconomic instability and unstable working conditions, compared with employed individuals. (21) Another possibility is that a majority of selfemployment may be forced self-employment, and therefore forced self-employment may have high stress and high burden, resulting in cardiovascular risk. However, given the nature of the observational study, correlation does not imply causation. The existence of co-existing or preexisting medical conditions in some people may prevent job employment or lead to forced selfemployment. Several studies showed that individuals who have pre-existing medical conditions such as HTN, DM, CAD are associated with problems in obtaining employment. In addition, pre-existing medical conditions are associated with self-reported job insecurity. (22) (23) (24) (25) However, in this cohort, we could not differentiate between selective self-employment or forced self-employment. A prior study suggested that involuntary job loss can be considered as a cardiovascular risk factor (26) , while selective self-employment is associated with better health status than forced self-employment because of healthy people perhaps self-selected into selfemployment.(2) Moreover, a subgroup of forced self-employment may already have underlying diseases, chronic illness, or mental disabilities and, therefore, could not work as an employee.

Most importantly, occasional natural disasters (e.g., floods, hurricanes, tornadoes) or infectious disease outbreaks (e.g., COVID-19 or 1918 influenza pandemics) may turn employed individuals towards forced self-employment and damage business owners due to event cancellation, supply chain losses, or exposure liabilities.

However, these factors are probably dependent on the company and a country's work culture, local and national policy. For example, known as an intense work culture in Japan, a study in the Japanese population showed no significant difference in cardiovascular risk and mortality between employed individuals and self-employed. (27) In contrast, a study reported that self-employed individuals in European countries are more satisfied with their lives than employed individuals.(28) The self-employed had better self-rated health and workability than employed individuals in the Netherlands(29), while higher cardiovascular mortality among selfemployed men and women than among other occupational classes in Sweden. (5) As such, it is important to understand these differences to promote a healthy work culture among selfemployed individuals in the US.

The present study has certain limitations. First, there may be residual or unmeasured confounders due to undiagnosed or latent risk factors. For example, the exact mechanisms that underlie the association between self-employment and cardiovascular risk may be confounded by other lifestyle factors (e.g., unhealthy diet, infrequent exercise, poor sleep hygiene, or long working hours). Second, this analysis was cross-sectional in nature, and therefore we could not infer causality. Third, as discussed earlier, those with poor health status, particularly established cardiovascular risk, may be forced into self-employment. Last, we could not find a difference in job details. One study (30) showed mortality is lower among those self-employed who run a limited liability company than among paid employees.

We found a significant association between self-employment and a higher prevalence of cardiovascular risk, including DM, HTN, HLD, HF, stroke, and CAD, than in the US general population. Further prospective studies are urgently needed to establish the optimal preventive strategy for reducing cardiovascular risks in self-employed individuals. 

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