Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts


Vimaleswaran, KS; Berry, DJ; Lu, C; Tikkanen, E; Pilz, S; Hiraki, LT; Cooper, JD; Dastani, Z; LI, R; Houston, DK; Wood, AR; Michaelsson, K; Vandenput, L; Zgaga, L; Yerges-Armstrong, LM; McCarthy, MI; Dupuis, J; Kaakinen, M; Kleber, ME; Jameson, K; Arden, N; Raitakari, O; Viikari, J; Lohman, KK; Ferrucci, L; Melhus, H; Ingelsson, E; Byberg, L; Lind, L; Lorentzon, M; Salomaa, V; Campbell, H; Dunlop, M; Mitchell, BD; Herzig, KH; Pouta, A; Hartikainen, AL; Streeten, EA; Theodoratou, E; Jula, A; Wareham, NJ; Ohlsson, C; Frayling, TM; Kritchevsky, SB; Spector, TD; Richards, JB; Lehtimaki, T; Ouwehand, WH; Kraft, P; Cooper, C; Marz, W; Power, C; Loos, RJF; Wang, TJ; Jarvelin, MR; Whittaker, JC; Hingorani, AD; Hypponen, E; Genetic Invest Anthropometric, Trai; (2013) Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts. PLoS medicine, 10 (2). ISSN 1549-1277 DOI: https://doi.org/10.1371/journal.pmed.1001383

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Abstract

Background: Obesity is associated with vitamin D deficiency, and both are areas of active public health concern. We explored the causality and direction of the relationship between body mass index (BMI) and 25-hydroxyvitamin D [25(OH) D] using genetic markers as instrumental variables (IVs) in bi-directional Mendelian randomization (MR) analysis. Methods and Findings: We used information from 21 adult cohorts (up to 42,024 participants) with 12 BMI-related SNPs (combined in an allelic score) to produce an instrument for BMI and four SNPs associated with 25(OH) D (combined in two allelic scores, separately for genes encoding its synthesis or metabolism) as an instrument for vitamin D. Regression estimates for the IVs (allele scores) were generated within-study and pooled by meta-analysis to generate summary effects. Associations between vitamin D scores and BMI were confirmed in the Genetic Investigation of Anthropometric Traits (GIANT) consortium (n = 123,864). Each 1 kg/m(2) higher BMI was associated with 1.15% lower 25(OH) D (p = 6.52x10(-27)). The BMI allele score was associated both with BMI (p = 6.30x10(-62)) and 25(OH) D (20.06% [95% CI -0.10 to -0.02], p = 0.004) in the cohorts that underwent meta-analysis. The two vitamin D allele scores were strongly associated with 25(OH) D (p <= 8.07x10(-57) for both scores) but not with BMI (synthesis score, p = 0.88; metabolism score, p = 0.08) in the meta-analysis. A 10% higher genetically instrumented BMI was associated with 4.2% lower 25(OH) D concentrations (IV ratio: -4.2 [95% CI -7.1 to -1.3], p = 0.005). No association was seen for genetically instrumented 25(OH) D with BMI, a finding that was confirmed using data from the GIANT consortium (p >= 0.57 for both vitamin D scores). Conclusions: On the basis of a bi-directional genetic approach that limits confounding, our study suggests that a higher BMI leads to lower 25(OH) D, while any effects of lower 25(OH) D increasing BMI are likely to be small. Population level interventions to reduce BMI are expected to decrease the prevalence of vitamin D deficiency.

Item Type: Article
Faculty and Department: Faculty of Epidemiology and Population Health > Dept of Non-Communicable Disease Epidemiology
PubMed ID: 23393431
Web of Science ID: 315592800005
URI: http://researchonline.lshtm.ac.uk/id/eprint/856568

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