Abstract
Objective To assess whether body mass index (BMI) has a causal effect on social and socioeconomic factors, including whether both high and low BMI can be detrimental.
Design Mendelian Randomization, using genetic variants for BMI to obtain unconfounded estimates, and non-linear Mendelian Randomization.
Setting UK Biobank.
Participants 378,244 men and women of European ancestry, mean age 57 (SD 8 years).
Main outcome measures Townsend deprivation index, income, age completed full time education, degree level education, job class, employment status, cohabiting relationship status, participation in leisure and social activities, visits from friends and family, and having someone to confide in.
Results Higher BMI was causally associated with higher deprivation, lower income, fewer years of education, lower odds of degree-level education and skilled employment. For example, a 1 SD higher genetically-determined BMI (4.8kg/m2 in UK Biobank) was associated with £1,660 less income per annum [95%CI: £950, £2,380]. Non-linear Mendelian Randomization provided evidence that both low BMI (bottom decile, <22kg/m2) and high BMI (top seven deciles, >24.6kg/m2) can increase deprivation and reduce income. In men only, higher BMI was related to lower participation in leisure and social activities. There was no evidence of causal effects of BMI on visits from friends and family or in having someone to confide in. Non-linear Mendelian Randomization analysis showed that low BMI (bottom three deciles, <23.5kg/m2) reduces the odds of cohabiting with a partner or spouse for men, whereas high BMI (top two deciles, >30.7kg/m2) reduces the odds of cohabitation with a partner or spouse for women.
Conclusions BMI affects social and socioeconomic outcomes, with both high and low BMI being detrimental for some measures of SEP. This suggests that in addition to health benefits, maintaining healthy ranges of BMI across the population could have benefits both for individuals and society.
Footnotes
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Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: LDH receives grant and fellowship funding from the UK Medical Research Council; LDH, ARD, SH and FS receive grant funding from the Health Foundation; SEJ is funded by a grant from the UK Medical Research Council; no other relationships or activities that could appear to have influenced the submitted work.”
What is known?
Studies have demonstrated stigma and discrimination against people who are overweight or obese in social, educational and employment settings.
Mendelian Randomization, a technique that uses genetic data to overcome confounding and reverse causality, has provided evidence for a causal effect of higher BMI on lower socioeconomic position (SEP). It is reasonable to hypothesise that adverse socioeconomic effects might be particularly strong for very high BMI, and also evident for low BMI, but this has not been explored by previous studies.
It is not known whether BMI also has a causal effect on social outcomes, such as cohabitation with a partner/spouse, contact with friends/family, and participation in leisure activities.
What this study adds
Using Mendelian Randomization, we found evidence of sex-specific effects of BMI on likelihood of being in a cohabiting relationship with a partner or spouse: in men, lower BMI was associated with being less likely to live with a partner or spouse, whereas in women, higher BMI was associated with being less likely to live with a partner or spouse.
We found evidence of causal effects of BMI on several domains of SEP (income, deprivation, education, skilled employment), with BMIs at both ends of the distribution (both high and low BMI) leading to lower income and higher levels of deprivation. Higher BMI was associated with lower participation in leisure activities in men but not women; effects of BMI on other measures of social contact were not observed.