According to scientists reporting in the journal PLoS Medicine, obesity can lead to a lack of vitamin D circulating in the human body.
This image illustrates calcium regulation in the human body, the role of vitamin D is shown in orange (Mikael Häggström)
Vitamin D, which is essential for healthy bones as well as other functions, is made in the skin after exposure to sunlight but can also be obtained through the diet and through supplements.
While previous studies have linked vitamin D deficiency with obesity, the PLoS Medicine study sought to establish the direction of causality i.e. whether a lack of vitamin D triggers a weight gain, or whether obesity leads to the deficiency.
The scientists used genetic markers derived from an analysis of 21 adult cohort groups (up to 42,000 participants) to explore the link between body mass index (BMI) and genes associated with the synthesis and metabolism of vitamin D. Associations between vitamin D and BMI were further confirmed using data from another genetic consortium with over 123,000 participants.
They found that a 10 per cent rise in BMI was linked to a 4 per cent drop in concentrations of vitamin D in the body.
Overall, the findings suggest that a higher BMI leads to lower levels of available vitamin D, while the effect of a lack of vitamin D on BMI appears to be very small.
The association between obesity and vitamin D status found here was consistent between genders, being apparent both in men and in women, and in younger and older age groups.
“Efforts to tackle obesity should thus also help to reduce levels of vitamin D deficiency in the population,” said lead author Dr Elina Hypponen of the University College London’s Institute of Child Health.
The results suggest that although increases in vitamin D are not likely to help with weight regulation, increased risk of vitamin D deficiency could contribute to the adverse health effects associated with obesity.
“Vitamin D deficiency is an active health concern around the world. While many health messages have focused on a lack of sun exposure or excessive use of suncreams, we should not forget that vitamin D deficiency is also caused by obesity,” Dr Hypponen said.
“Our study highlights the importance of monitoring and treating vitamin D deficiency in people who are overweight or obese, in order to alleviate adverse health effects caused by a lack of vitamin D.”
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Bibliographic information: Vimaleswaran KS et al. 2013. Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts. PLoS Med 10 (2): e1001383; doi: 10.1371/journal.pmed.1001383
