Megadose is a relative term, particularly in terms of vitamin D. The current RDA for vitamin D is 600 IU for everyone up to age 70, and 800 IU for older people. Yet other experts say the RDA should be at least 2,000 IU and up to 8,000 IU for diabetes patients. The official position of the National Institutes of Health is that 4,000 IU is the tolerable upper limit. Side effects from vitamin D "overdose" are so rare -- although there have been cases -- that a 2009 issue of "Southern Medical Journal" discusses the mechanisms rendering it harmless in doses exceeding 50,000 IU daily. As with any supplement, check with your doctor before taking it, especially if you have health problems or are taking other medicines.
Benefits at 800 IU
The Nurses' Health Study is an investigation of health and diet in 238,000 female nurse practitioners. Researchers reporting in the March 2006 issue of "Diabetes Care" followed 83,779 of the participants with no history of diabetes for 20 years. During that time, 4,843 of the women developed Type 2 diabetes. Vitamin D intake was assessed every two to four years. The researchers found that nurses who supplemented 800 IU vitamin D a day reduced their risk of diabetes by 20 percent compared with women who supplemented 400 IU per day.
Benefits at 1,332 IU
Researchers reporting in the May 2003 issue of "International Journal of Clinical Practice" investigated insulin action and secretion in relation to vitamin D intake. The researchers supplemented 10 women with Type 2 diabetes and 17 healthy female controls with 1,332 IU vitamin D per day for one month. The female controls were matched for age and weight with the diabetic women. The researchers reported a 21.4 percent decrease in insulin resistance and a 34 percent decrease in insulin secretion in the diabetes group. In short, the diabetics eliminated more blood sugar using less insulin after one month of supplementation.
2,000 IU Benefits for Children
Researchers reporting in the November 2001 edition of "Lancet" examined over 12,000 Finnish women scheduled to give birth in 1966. One year later, 10,821 of the women reported for follow-up, and 81 of them were diagnosed with Type 1 diabetes. The researchers found that women who supplemented vitamin D either regularly or irregularly ran a 20 percent lower risk of acquiring the disease compared with those who did not supplement at all. Significantly, their children who supplemented 2,000 IU per day cut their risk of developing Type 1 diabetes by 50 percent.
Up to 8,000 IU
A group of researchers reporting in the February 2011 issue of "Anticancer Research" conducted a study of 3,667 men and women whom they followed for five years. Every six months, the researchers tested the participants' blood levels of vitamin D and correlated them with the risk of developing a variety of diseases, including cancers and diabetes. The researchers found that daily intakes of vitamin D by adults in the range of 4,000 to 8,000 IU were needed to maintain blood levels of vitamin D metabolites in the range needed to reduce the risk of these diseases by about half.
References
- "Southern Medical Journal"; The Lack of Vitamin D Toxicity with Megadose of Daily Ergocalciferol (D2) Therapy: a Case Report and Literature Review; David Stephenson and Alan Peiris; July 2009
- "Diabetes Care"; Vitamin D and Calcium Intake in Relation to Type 2 Diabetes in Women; Anastassios Pittas et al., March 2006
- "International Journal of Clinical Practice"; The Effect of Vitamin D3 on Insulin Secretion and Peripheral Insulin Sensitivity in Type 2 Diabetic Patients; A. Borissova et al.; May 2003
- "Lancet"; Intake of Vitamin D and Risk of Type 1 Diabetes: a Birth-Cohort Study; Elina Hyppönen et al.; November 2001
- "Anticancer Research"; Vitamin D Supplement Doses and Serum 25-Hydroxyvitamin D in the Range Associated with Cancer Prevention; Cedric Garland et al.; February 2011
- NIH: Supplement Facts: Vitamin D
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