Vitamin D deficiency linked more closely to diabetes than obesity

Vitamin D is an important fat-soluble vitamin required by the human body in order to maintain healthy status. Vitamin D is obtained through an assortment of sources, including diet, supplements, and exposure to the sun, where ultraviolet rays from sunlight trigger vitamin D synthesis when they strike the skin (Institute of Medicine Food and Nutrition Board, 2010; Tai, Need, Horowitz, & Chapman, 2008). Vitamin D deficiency can be the result of limited exposure to sunlight, inadequate dietary consumption of vitamin D, inability of the kidneys to convert it to its active form, or insufficient absorption of the digestive tract of vitamin D (Institute of Medicine Food and Nutrition Board, 2010). Both vitamin D deficiency and glucose metabolism disorders like diabetes are on the rise among the general population. Popular news sources all over the internet explosively list off the reasons why we need to catch some rays for that ‘sunshine’ vitamin, but other stories such as one published by Men’s Journal titled “Vitamin D deficiency increases risk for diabetes more than obesity” actually highlight an important recent finding regarding vitamin D’s importance in our bodies, even if it does reduce its credibility talking about scientific findings by including as the article photo a picture of a tanned and shirtless athletic-looking man laying out while soaking up some rays. This story was however based off a 2015 study published in the Journal of Clinical Endocrinology & Metabolism. The scientific article interestingly found that diabetic subjects had lower levels of vitamin D than subjects who did not have diabetes, regardless of their weight, helping to clarify the connection between these 3 variables. The study suggested that vitamin D deficiency and obesity may interact synergistically to heighten the risk of diabetes (Clemente-Postigo et al., 2015).

            Low levels of the active form of Vitamin D in the body have been linked to obesity and diabetes in observational studies. To become active, vitamin D is hydroxylated twice, first in the liver to become 25-hydroxyvitamin D [25(OH)D] and then in the kidney to become physiologically active 1,25-dihydroxyvitamin D [1,25(OH)₂D] (Clemente-Postigo et al., 2015). In measuring vitamin D levels in the body, 25(OH)D is used because circulating 1,25(OH)₂D are not considered to be an effective indicator for vitamin D status as it does not decrease in levels until the deficiency is severe. Vitamin D is thought to play a role in glucose homeostasis due to its role in stimulating insulin production (Clemente-Postigo et al., 2015; Dutta et al., 2014). Thus, low vitamin D levels have been associated with increased insulin resistance and effects on insulin sensitivity, although the exact mechanisms are not yet understood (Tai et al., 2008). There is, however, evidence that vitamin D affects pancreatic cell function directly through binding to vitamin D receptors there or indirectly through their function regulating extracellular calcium levels and calcium movement through the β-cells of the pancreas.  

The aim of this study was to evaluate levels of active vitamin D based of diabetic status and weight of participants. As stated, 25(OH)D levels were shown to be closely associated to variables related to glucose metabolism, which supported vitamin D deficiency to be more closely related to glucose metabolism disorders than to obesity. There are, however, other recent studies that contradict these results (Clemente-Postigo et al., 2015; Dutta et al., 2014). Further studies are needed to confirm and understand the role of vitamin D and vitamin D receptors in diabetes.

Resources

Clemente-Postigo, M., Muñoz-Garach, A., Serrano, M., Garrido-Sánchez, L., Bernal-López, M. R., Fernández-García, D., … Macías-González, M. (2015). Serum 25-hydroxyvitamin D and adipose tissue vitamin D receptor gene expression: Relationship with obesity and type 2 diabetes. Journal of Clinical Endocrinology and Metabolism, 100(4), E591–E595. https://doi.org/10.1210/jc.2014-3016

Dutta, D., Mondal, S. A., Choudhuri, S., Maisnam, I., Hasanoor Reza, A. H., Bhattacharya, B., … Mukhopadhyay, S. (2014). Vitamin-D supplementation in prediabetes reduced progression to type 2 diabetes and was associated with decreased insulin resistance and systemic inflammation: An open label randomized prospective study from Eastern India. Diabetes Research and Clinical Practice, 103(3). https://doi.org/10.1016/j.diabres.2013.12.044

Institute of Medicine Food and Nutrition Board. (2010). Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press. Washington, DC.

Tai, K., Need, A. G., Horowitz, M., & Chapman, I. M. (2008). Vitamin D, glucose, insulin, and insulin sensitivity. Nutrition, 24(3), 279–285. https://doi.org/https://doi.org/10.1016/j.nut.2007.11.006