In this country, diabetes afflicts more than 20 million Americans and is the sixth leading cause of death; there is an immense need for blood sugar control . As with heart disease and cancer, there is a striking latitudinal association: people who live in sunny climates tend to have lower risk of diabetes. Northern Finns, for example, who experience only two hours of sunlight in December, have the world’s highest reported incidence of type 1 diabetes, and vitamin D supplementation is shown to reduce their risk of this disease. In 1966, 12000 Finnish babies were given 2000 IU vitamin D a day from one year of age and watched over the next thirty years. Those taking the vitamin D decreased their risk of developing type 1 diabetes by 80%. This same study showed that those children low in vitamin D at one year of age had a four-fold increased risk of developing type 1 diabetes.
In the US, the Third National Health and Nutrition Examination Survey (NHANES III) found that as blood levels of vitamin D rose, the risk for diabetes decreased, and those with the highest vitamin D levels had one-quarter the diabetes risks of those with the lowest vitamin D blood levels. In another light, a study by Borissova and colleagues in Bulgaria found that giving vitamin D supplements in the winter to adults with type 2 diabetes improved blood sugar control. Even in sunny Italy, vitamin D blood levels were significantly lower in patients with diabetes.
And what are the mechanisms by which vitamin D helps to prevent diabetes? We now know this nutrient enhances insulin output and insulin sensitivity, and people with a low level of vitamin D have poorly functioning insulin-producing cells and a poor response to insulin, even when their blood sugar levels are normal.
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