1. Among individuals with a higher body mass index, baseline vitamin D serum metabolite levels were lower compared to those with a lower body mass index.

2. A reduced efficacy of vitamin D supplementation was observed in individuals with a higher body mass index, which may be due to a blunted metabolism.

Evidence Rating Level: 2 (Good)

Vitamin D is an essential micronutrient and its relevance to various diseases such as rickets and osteomalacia is well established. New research suggests that vitamin D insufficiency may be linked to obesity and excess body weight. The Vitamin D and Omega-3 Trial (VITAL) was a completed randomized controlled trial that investigated the interactions between circulating total 25-hydroxyvitamin D (25-OHD) and obesity. A total of 16,515 adult participants free of cancer and cardiovascular disease at baseline were enrolled. These participants contributed baseline blood samples and reported their height and body weight on a questionnaire. Participants were then followed up after two years. In the original VITAL study, participants were randomized into two groups—the vitamin D supplementation group and the placebo group. The results of this cohort analysis showed that prior to randomization, serum total 25-OHD values were lower at higher BMI categories. However, following randomization, the intervention group who received vitamin D supplementation demonstrated an increase in total 25-OHD levels, but these increases were significantly lower in those with a higher BMI. This suggests that while vitamin D supplementation can increase vitamin-D-related serum biomarkers, there was a reduced response among individuals who were overweight at baseline. In conclusion, this study interestingly proposes a modified response to vitamin D supplementation and subsequent effects on health outcomes in individuals with a higher body-mass index. There are several limitations that should be noted. For instance, while the randomized nature of the study strengthened the validity of these results, certain factors such as adherence to study medication or loss to follow-up were not accounted for in the methodology. As well, the same amount of vitamin D supplementation was provided to all participants regardless of baseline BMI, but individuals of varying weights may have different vitamin requirements. Nevertheless, this post-hoc study of a large randomized clinical trial suggests that individuals of a higher weight may respond experience a blunted response to vitamin D supplementation. Further research into the mechanisms behind this phenomenon is warranted.

Click to read the study in JAMA Network Open

Image: PD

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