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Effects of body mass index on relationship status, social contact, and socioeconomic position: Mendelian Randomization and within-family study in UK Biobank

Research output: Contribution to journalArticle

Original languageEnglish
Article numberdyz240
Number of pages12
JournalInternational Journal of Epidemiology
DateAccepted/In press - 1 Nov 2019
DatePublished (current) - 4 Dec 2019


BackgroundWe assessed whether body mass index (BMI) affects social andsocioeconomic outcomes.
MethodsWe used Mendelian Randomization (MR), non-linear MR and non-genetic and MR within-sibling analyses, to estimate relationships of BMI with six socioeconomic and four social outcomes in 378,244 people of European ancestry in UK Biobank.
ResultsIn MR of minimally-related individuals, higher BMI was related to higher deprivation, lower income, fewer years of education, lower odds of degree-level education and skilled employment. Non-linear MR suggested both low (bottom decile, <22kg/m2) and high BMI (top seven deciles, >24.6kg/m2) increase deprivation and reduce income. Non-genetic within-sibling analysis supported an effect of BMI on SEP; precision in within-sibling MR was too low to draw inference about effects of BMI on SEP. There was some evidence of pleiotropy, with MR Egger suggesting limited effects of BMI on deprivation, althoughprecision of these estimates is also low. Non-linear MR suggested that low BMI (bottom three deciles, <23.5kg/m2) reduces the odds of cohabiting with a partner or spouse in men, whereas high BMI (top two deciles, >30.7kg/m2) reduces the odds of cohabitation in women. Both non-genetic and MR within-sibling analysis supported this sex-specific effect of BMI on cohabitation. In men only, higher BMI was related to lower participation in leisure and socialactivities. There was little evidence that BMI affects visits from friends and family or having someone to confide in.
ConclusionsBMI may affect social and socioeconomic outcomes, with both high and low BMI being detrimental for SEP, although larger within-family MR studies may help to test the robustness of MR results in unrelated individuals. Triangulation of evidence across MR and within-family analyses supports evidence of a sex-specific effect of BMI on cohabitation.

    Research areas

  • body mass index, obesity, socioeconomic, cohabitation, social contact, siblings, Mendelian randomisation

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