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Nutrition

Obesity leads to vitamin D deficiency

Vitamin D deficiency is associated with multiple health concerns
Study provides evidence for the role of obesity as a causal risk factor for the development of vitamin D deficiency
The findings will further understanding of obesity and help to reduce levels of vitamin D deficiency in the population

Obesity can lead to vitamin D deficiency, according to a study published in the journal PLOS Medicine. The study authors, from the University College London’s Institute of Child Health, believe that the findings will further our understanding of obesity and help to reduce levels of vitamin D deficiency in the population.

"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,” said lead author of the study, Dr Elina Hypponen. “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."

Although previous studies have found an association between vitamin D deficiency and obesity, the exact causality - whether a lack of vitamin D triggers a weight gain or whether obesity leads to the deficiency - has yet to be determined.

Gene variants do not change over time and are inherited randomly. Therefore, if a lower vitamin D status leads to obesity, genetic variants associated with lower vitamin D deficiency should be associated with higher BMI, and if obesity leads to a lower vitamin D status, then genetic variants associated with higher BMI should be associated with vitamin D concentrations.

Study design

The researchers study used genetic markers derived from an analysis of 21 adult cohort groups (42,024 participants) to explore the link between BMI and genes associated with the synthesis and metabolism of vitamin D.

They selected 12 established BMI-related single nucleotide polymorphism SNPs for analysis and four vitamin D-related SNPs (DHCR7- rs12785878, CYP2R1- rs10741657, GC- rs2282679, and CYP24A1- rs6013897) were chosen.

To assess the BMI relationship with vitamin D deficiency and vice versa, the researchers created a weighted score by multiplying each SNP (coded as 0–2) by a weight based on its effect size with BMI.

To confirm their findings on the association between the vitamin D-related SNPs, they also used the summary statistics for the four vitamin D-related SNPs from the Genetic Investigation of Anthropometric Traits (GIANT) study consortium (including over 123,000 participants).

Results

The researchers report that in the meta-analyses of 21 studies, each unit increase in BMI was associated with 1.15% lower concentrations of vitamin D, after adjusting for age, sex, laboratory batch, month of measurement, and principal components. The inverse association between BMI and vitamin D was stronger among the studies from North America than those from Europe.

They also reported that BMI was associated with vitamin D deficiency, with each 10% increase in BMI resulting in a 4.2% decrease in vitamin D concentrations (p=0.005).

However, the found little evidence for a causal effect of vitamin D on BMI (p≥0.08).  The lack of association of the vitamin D with BMI was confirmed using the GIANT data (p≥0.57).

Of the 12 individual BMI SNPs, the SNP for the fat mass and obesity-associated protein was the only one that showed evidence of a univariate association with vitamin D (p=0.050), whilst none of the four vitamin D SNPs were individually associated with BMI (p≥0.10). The lack of association of the four vitamin D SNPs with BMI was further confirmed using the summary data from the GIANT consortium (p>0.30 for all the SNPs).

Conclusion

The authors concluded that their 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 was consistent between genders and in younger and older age groups.

“Higher BMI leads to lower vitamin D status, providing evidence for the role of obesity as a causal risk factor for the development of vitamin D deficiency,” the authors write. “Together with the suggested increases in vitamin D requirements in obese individuals, our study highlights the importance of monitoring and treating vitamin D deficiency as a means of alleviating the adverse influences of excess adiposity on health. Our findings suggest that population level interventions to reduce obesity would be expected to lead to a reduction in the prevalence of vitamin D deficiency.”

The study was supported by the British Heart Foundation and the UK Medical Research Council.

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