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Getting optimal amounts of vitamin D may have a positive influence on blood-sugar levels, possibly preventing diabetes and “metabolic syndrome,” a group of metabolism abnormalities associated with insulin resistance.

More than 10 million Americans suffer from diabetes, which often leads to heart disease, kidney damage, nervous system impairments, and other health problems. Even more people have "metabolic syndrome", which is characterized by heart-disease risk factors such as high blood pressure, elevated levels of triglycerides, low levels of HDL (“good”) cholesterol, and abdominal obesity. PCOS shares many of attributes of metabolic syndrome, and women with PCOS are more likely to develop diabetes and cardiovascular disease.

In many cases of polycystic ovarian syndrome, diabetes and metabolic syndrome, insulin resistance is a significant contributing factor. Insulin is a hormone produced by the pancreas that helps transport glucose 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 a new study, vitamin D status 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.

As many as 40% of Americans may have vitamin D deficiency. Vitamin D is present in only a few foods, such as cod-liver oil, oily fish (salmon, mackerel, sardines), and vitamin D-fortified dairy products and breakfast cereals.

Most of the vitamin D in your body is manufactured in the skin after exposure to sunlight. People who don't receive adequate amounts of sun exposure are at risk of developing vitamin D deficiency.

According to one report, adequate vitamin D levels can be achieved by daily exposure of your hands, face, and arms to sunlight for one-quarter the time it would take to produce a light pinkness of the skin. If you're unable to obtain that amount of sunlight exposure, vitamin D supplementation should be considered. The amount recommended by most doctors ranges from 400 IU 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.

Source: Chiu, KC et al, Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction, Am. J. Clinical Nutrition, May 2004; 79:820-825