Vitamin D: A possible ally in the fight against diabetes

The Bottom Line

  • Vitamin D can be obtained in small amounts from food, sunlight, or supplements; and can help regulate insulin levels.
  • Vitamin D supplementation may help lower average blood sugar levels in people with type 2 diabetes; and is especially effective in people who also have a vitamin D deficiency, and are non-obese and deficient. 
  • Supplementation for more than 12 weeks at ≥ 1000 IU/day may be most beneficial. 

The many positive health impacts of vitamin D have dominated the supplement world in recent years. Similarly, the growing worldwide epidemic of type 2 diabetes has also been in the spotlight – with an estimated 400 million people affected currently, and this number expected to be 642 million by 2040 (1;2). As type 2 diabetes rates continue to soar, there is an urgent need to find effective ways to tackle this disease. Vitamin D supplementation has emerged as a possible solution (1). But how effective is it really?

Known as the “sunshine vitamin”, vitamin D is created in your skin in response to direct sunlight (3;4;5). However, the amount of vitamin D created can be hindered by a variety of factors including cloud cover, time of day, and smog (3). Vitamin D is also found in small amounts in some foods such as oily fish (mackerel, sardines and tuna) (3;4;5), as well as foods fortified with vitamin D such as dairy products, breakfast cereal, and orange juice (3). Most foods however, are not a great source of vitamin D (3;4;5), which has resulted in many taking supplements to boost their vitamin D levels. In fact, almost 34% of Canadians took some kind of supplement that contained vitamin D in 2015 (6).

Many people with diabetes are low in vitamin D (7). This is an important finding because vitamin D is known to help regulate insulin levels (8). New studies have assessed if vitamin D supplementation helps in the management of type 2 diabetes (1).

What the research tells us

A recent systematic review and meta analysis explored whether vitamin D supplementation improved blood sugar control in adults with type 2 diabetes. Studies included in the review administered vitamin D at varying doses, frequencies, and lengths of time, and in different forms such as tablets, drinks, and injections.

The findings of the review indicated that overall, average blood sugar levels may be reduced with vitamin D supplementation, but not fasting blood sugar levels. However, these effects were not consistent across all participants. For example, individuals who were non-obese seemed to experience improvements in average blood sugar levels, while individuals with a vitamin D deficiency, as well as those who were both non-obese and deficient in vitamin D seemed to experience reductions in both average and fasting blood sugar levels. People with type 2 diabetes who were obese or not classified as vitamin D deficient did not experience benefits with supplementation.

When it comes to blood sugar control, adults with type 2 diabetes who were deficient in vitamin D and who were of a healthy weight were likely to benefit the most from vitamin D supplementation. The greatest effects occurred when supplements were taken for longer than 12 weeks and at a dose of ≥ 1000 IU per day. While more research is still needed to confirm these results, currently there is reason to believe that vitamin D can have a role to play in managing type 2 diabetes for some people (1).

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  1. Wu C, Qiu S, Zhu X, et al. Vitamin D supplementation and glycemic control in type 2 diabetes patients: A systematic review and meta-analysis. Metabolism. 2017; 73:67-76. doi: 10.1016/j.metabol.2017.05.005. 
  2. International Diabetes Federation. IDF diabetes atlas – 8th edition. [Internet] 2017. [cited June 2018]. Available from
  3. National Institutes of Health. Vitamin D fact sheet for health professionals. [Internet] 2017. [cited June 2018]. Available from
  4. Houghton LA, Vieth R. The case against ergocalciferol (vitamin D2) as a vitamin supplement. Am J Clin Nutr. 2006; 84(4):694-697.
  5. Avenell A, Mak JC, O’Connell D. Vitamin D and vitamin D analogues for preventing fractures in post-menopausal women and older men. Cochrane Database of Syst Rev. 2014; 4:CD000227. doi: 10.1002/14651858.CD000227.pub4.
  6. Statistics Canada. Use of nutritional supplements, 2015. [Internet] 2017. [cited June 2018]. Available from
  7. Pittas AG, Lau J, Hu FB, et al. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. J Clin Endocrinol Metab. 2007; 92(6):2017-2029. doi: 10.1210/jc.2007-0298. 
  8. Mitri J, Pittas AG. Vitamin D and diabetes. Endocrinol Metab Clin North Am. 2014; 43(1):205-232. doi: 10.1016/j.ect.2013.09.010. 

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