Vitamin D
Background
Vitamin D is a fat soluble vitamin found in fish liver oil that protects against the complications of diabetes. In addition, vitamin D is necessary for the production of insulin. Antibiotics, laxatives, synthetic fat substitutes, and cholesterol-lowering drugs all interfere with vitamin A and D absorption.
Vitamin D is obtained naturally from two sources, exposure to sunlight and dietary consumption. Vitamin D-3 (cholecalciferol) is the form of vitamin D produced in the skin and consumed in the diet. Vitamin D-2 (ergocalciferol), produced by irradiating fungi, is a much less effective and potentially more toxic source of vitamin D. It is not recommended. In addition to supplementation, sources of vitamin D (other than cow’s milk fortified with vitamin D) include fish oil, egg yolks, butter, liver, and some fortified breakfast cereals. Exposure to UV rays found in sunlight enables the body to manufacture vitamin D.
Clinical Studies
Vitamin D, originally believed to influence only calcium absorption and bone density, is now appearing to play an important role immune system modulation.
Type I Prevention
In a study of more than 12,000 infants in Finland, it was found that vitamin D supplementation was associated with a decreased frequency of Type I diabetes. In fact, regular infants who received the recommend vitamin D supplementation (2,000 IU/day) in the first year of life had an 88% less chance of developing Type I diabetes by age 30 as compared to those infants receiving no supplementation. In addition, children suspected of having rickets during the first year of life (an indicator of low vitamin D status) had a three times higher chance of developing diabetes compared with those children without rickets. The authors conclude that “ensuring adequate vitamin D supplementation for infants could help to reverse the increasing trend in the incidence of type 1 diabetes.” It should be noted that the 2,000 IU/day dose recommended is much higher than the North American RDA of 400 IU/day. In this study, infants supplemented with less than 2,000 IU/day did not do as well.
A birth-cohort study undertaken in London over a period of 31years studied the effect of vitamin D in diabetes prevention. Knowing that supplementation with this vitamin reduces the risk of IDDM in animals, the researchers followed more than 10,000 children to measure the effect of vitamin D supplementation in humans. Daily supplementation with 2000 IU of vitamin D (4.5 times the recommended daily allowance) was associated with reduced risk of the development of Type I diabetes.
Insulin Resistance
Low circulating vitamin D levels are also associated with insulin resistance and beta-cell dysfunction, not only in diabetics, but also in healthy young non-diabetic adults. Healthy adults with higher serum vitamin D levels had significantly lower 60-minute, 90-minute, and 120-minute postprandial (after eating) glucose levels than those who were vitamin D deficient. Those with higher vitamin D status also had significantly better insulin sensitivity. The authors noted that, compared with the common oral diabetic pharmaceutical metformin, which improves insulin sensitivity by 13%, higher vitamin D status correlated with a 60% improvement in insulin sensitivity. In addition, a recent clinical trial used 1332 IU per day of vitamin D for only 30 days in 10 women with Type II diabetes. Even this relatively low level of vitamin D supplementation over a short period was shown to improve insulin sensitivity by a remarkable 21%.
Doseage
It is possible that the typical dosage of vitamin D used in supplements, based on the RDA values, is enough to ward off frank deficiency, but falls far short of optimal levels. Full-body exposure to ultraviolet light can produce 10,000 to 25,000 IU of vitamin D-3 per day, much higher than the RDA, and likely more accurately reflecting our needs. It is possible that the majority of studies in adults have used inadequate doses of vitamin D and that is why they may have failed to identify therapeutic benefits from vitamin D supplementation. A more reasonable vitamin D dose for adult studies may be 5,000 to 10,000 IU per day, continued for at least 3 to 4 months until vitamin D levels plateau. Vitamin D therapy should only be undertaken with the guidance of a healthcare practitioner familiar with its use.
