Recent studies of vitamin D suggest that it may play a role in the development of diabetes and its complications. Whether vitamin D supplements should be routinely given to people with diabetes is unclear.
Vitamin D is a hormone that helps regulate calcium levels
Although most vitamins are micronutrients that are consumed as part of a healthy diet, the active form of vitamin D is actually a substance that is produced from precursors in response to decreased calcium levels and/or increased parathyroid hormone levels. The role of vitamin D is to increase calcium levels; calcium levels are regulated by vitamin D working in conjunction with two other hormones, parathyroid hormone and calcitonin.
Vitamin D exists in several forms. A simplified version of the very complex nomenclature for these forms follows:
- Vitamin D1: is a precursor of active vitamin D. It is converted by an enzyme in the liver to an intermediate form called vitamin D2.
- Vitamin D2: also known as ergocalciferol; calcidiol; 25-hydroxy-vitamin D; 25OHD. Vitamin D2 is converted to the active form (Vitamin D3) by an enzyme in the kidneys.
- Vitamin D3: also known as cholecalciferol; calcitriol; 1,25-dihydroxy-vitamin D; 1,25-dihydroxycholecalciferol; 1,25-OHD. This is the active form of vitamin D.
Sources of vitamin D include sunlight's effect on vitamin D precursors in the skin, or from dietary intake of the precursors, or from pharmaceutical preparations of vitamin D3.
Vitamin D deficiency is the cause of two bone disorders, called rickets (in children) and osteomalacia (in adults). Vitamin D deficiency may also predispose to the development of both type 1 and type 2 diabetes.
Vitamin D excess (also called hypervitaminosis D) is rare, and is usually caused by taking massively excessive amounts of vitamin D supplements. It is associated with high calcium levels, and has symptoms of nausea, vomiting, decreased appetite, confusion, and possible heart rhythm abnormalities or kidney stones.
How much vitamin D should be taken? One authority states "The Institute of Medicine recommends that children and adults up to age 50 get 200 international units (IU) of vitamin D daily. The recommendation for adults over age 50 is 400 to 600 IU daily. However, many health experts consider these recommendations to be too low. The American Academy of Pediatrics, for instance, now recommends that children and adolescents get 400 IU of vitamin D daily. Many experts now 'unofficially' recommend that adults get as much as 1,000 to 2,000 IU of vitamin D daily. In addition, it's likely that the vitamin D guidelines will be revised upward."
Role of Vitamin D in diabetes
The observation that vitamin D deficiency impairs both insulin synthesis and insulin secretion suggests that it may somehow play a role in the development of the metabolic syndrome and type 2 diabetes; this could be a direct effect of vitamin D, or be associated with calcium levels. Also, epidemiologic studies have indicated a role of vitamin D deficiency in development of type 1 diabetes. Other studies have indicated that vitamin D may be important in the prevention of cardiovascular complications of diabetes.
Should people with diabetes take vitamin D supplements?
The American Diabetes Association, in a diabetes research summary, states that "more studies need to be conducted in order to say for certain that taking more calcium and vitamin D is a good way to prevent diabetes and its complications."
In a separate position statement, the ADA stated that "there is no clear evidence of benefit from vitamin or mineral supplementation in people with diabetes (compared with the general population) who do not have underlying deficiencies."
As of this writing, there is no organization recommending routine vitamin D supplementation for people with diabetes.
Also see
Vitamin D and diabetes. At PubMed.
http://www.ncbi.nlm.nih.gov/pubmed/15971062
Role of vitamin D in the pathogenesis of type 2 diabetes mellitus. At PubMed.
http://www.ncbi.nlm.nih.gov/pubmed/18269634
Dietary Calcium, Vitamin D, and the Prevalence of Metabolic Syndrome in Middle-Aged and Older U.S. Women. Diabetes Care.
http://care.diabetesjournals.org/content/28/12/2926.full
Vitamin D Linked to Type 1 Diabetes. At ADA website.
http://www.diabetes.org/news-research/research/access-diabetes-research/vitamin-d-linked-to-type1-diabetes.html
Vitamin D and Diabetes: Looking for links between the sunshine vitamin and diabetes. At Forecast magazine.
http://forecast.diabetes.org/magazine/your-ada/vitamin-d-and-diabetes
Position Statement On Vitamin D. American Academy of Dermatology.
http://www.aad.org/forms/policies/uploads/ps/ps-vitamin%20d.pdf
Doctors Double Vitamin D for Children. At Forecast magazine.
http://forecast.diabetes.org/forecast/newsbriefs/doctors-double-vitamin-d-children
Nutrition Recommendations and Interventions for Diabetes.
A position statement of the American Diabetes Association.
http://care.diabetesjournals.org/content/31/Supplement_1/S61.full
Nutrition and Bone Health: Calcium and Vitamin D: Important at Every Age. From the NIH.
http://www.niams.nih.gov/Health_Info/Bone/Bone_Health/Nutrition/default.asp#d
