Vitamin D and Diabetes Prevention

Getting optimal amounts of vitamin D may have a positive influence on blood-sugar levels, possibly preventing diabetes and the “metabolic syndrome,” a group of metabolism abnormalities associated with insulin resistance, reports a study in the American Journal of Clinical Nutrition (2004;79:820–5).

More than 10 million Americans suffer from type 2 (adult onset) diabetes, a chronic disease that often leads to heart disease, kidney damage, nervous-system impairments, and other problems. An even greater number of people have the metabolic syndrome, which is characterized by various heart-disease risk factors such as high blood pressure, elevated levels of triglycerides, low levels of HDL (“good”) cholesterol, and abdominal obesity.

In many cases of type 2 diabetes and in most cases of metabolic syndrome, insulin resistance is a significant contributing factor. Insulin is a hormone produced by the pancreas that helps transport glucose (the body’s main form of sugar) from the bloodstream into the cells, where it is used to produce energy. In people with insulin resistance, plenty of insulin is available, but the body has an impaired capacity to recognize or respond to its hormonal signal.

In the new study, vitamin D status (as determined by blood levels of 25-hydroxyvitamin D) was assessed in a group of healthy young volunteers. The degree of insulin resistance and the capacity of the pancreas to secrete insulin were also measured in each volunteer. The results showed that lower blood levels of vitamin D were associated with a greater degree of insulin resistance and with weaker pancreatic function. Of those with subnormal vitamin D levels, 30% had one or more components of the metabolic syndrome, compared with only 11% of those with normal vitamin D levels. These results suggest that vitamin D deficiency increases the risk of insulin resistance or of the metabolic syndrome.

Vitamin D deficiency is far more common than most people realize, affecting as many as 40% of Americans, according to some studies. Vitamin D is present in only a few foods, such as cod-liver oil, oily fish (including salmon, mackerel, and sardines), and vitamin D–fortified dairy products and breakfast cereals. Most of the vitamin D in the human body is manufactured in the skin after exposure to ultraviolet light from the sun. People who do not receive adequate amounts of sun exposure are at risk of developing vitamin D deficiency. In addition, those with dark skin and elderly people have a reduced ability to produce vitamin D in response to sunlight exposure.

Fear of developing wrinkles or skin cancer causes many people in modern society to avoid the sun or use sunscreen; while these actions protect them against harmful rays, they also prevent the beneficial ultraviolet rays from reaching the skin, leading to insufficient sun exposure. According to one report, adequate vitamin D status can be achieved by daily exposure of one’s hands, face, and arms to sunlight for one-quarter the time it would take to produce a light pinkness of the skin. For people who are unable to obtain that amount of sunlight exposure, vitamin D supplementation may be worthwhile. The amount recommended by most doctors ranges from 400 to 1,000 IU per day. Although excessive doses of vitamin D can be toxic, recent research suggests that long-term use of 1,000 IU per day is safe.

Alan R. Gaby, MD, an expert in nutritional therapies, testified to the White House Commission on CAM upon request in December 2001. Dr. Gaby served as a member of the Ad-Hoc Advisory Panel of the National Institutes of Health Office of Alternative Medicine. He is the author of Preventing and Reversing Osteoporosis (Prima, 1994), and co-author of The Natural Pharmacy, 2nd Edition (Healthnotes, Prima, 1999), the A–Z Guide to Drug-Herb-Vitamin Interactions (Healthnotes, Prima, 1999), Clinical Essentials Volume 1 and 2 (Healthnotes, 2000), and The Patient’s Book of Natural Healing (Prima, 1999). A former professor at Bastyr University of Natural Health Sciences, in Kenmore, WA, where he served as the Endowed Professor of Nutrition, Dr. Gaby is the Chief Medical Editor for Healthnotes, Inc.

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