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
