New research suggests that people with diabetes may face an increased risk of heart disease if they have a deficiency of vitamin D. An article in Science News magazine cites a study at Washington University School of Medicine in St. Louis indicating that macrophages, the immune cells that normally fight heart disease by absorbing LDL cholesterol, may do their job too well in cases of vitamin D deficiency. Instead of helping to prevent heart disease in these patients, the macrophages may actually contribute to it.
Endocrinologist Carlos Bernal-Mizrachi and his colleagues tested blood samples from 76 obese people, average age 55, who had type 2 diabetes, high blood pressure and low vitamin D levels. From these samples, the researchers cultured macrophages and exposed the immune cells to LDL cholesterol (the bad kind). They found that macrophages from type 2 diabetes patients showed a greater tendancy to absorb excessive amounts of LDL when they were cultured without vitamin D than when they were bathed in the vitamin. This transformed the macrophages into cholesterol-filled foam cells, the building blocks of arterial plaque.
Previous research has suggested that vitamin D deficiency may contribute to the risk of heart disease, but this is the first indication of the cellular mechanism that actually causes the increased risk.
Foam cells are part of the debris that collects inside blood vessels, eventually forming a fibrous cap of plaque. When the plaque ruptures and a blood clot forms, a stroke or heart attack can occur.
The study found that non-diabetics showed much less of this effect than diabetic patients did.
Further research by the same group of scientists has shed light on the reason for these results. In diabetic people, vitamin D helps reduce stress to the endoplasmic reticulum, which controls many cell functions. Reducing stress causes the macrophages to absorb less LDL cholesterol. In cases of vitamin D deficiency, this stress reduction does not take place, and the macrophages absorb more LDL cholesterol than they should. The stress also contributes to inflammation, which releases proteins that degrade plaque and lead to cap breakdown.
Though the results are preliminary and more research will be done on this question in the future, it appears that people with diabetes should pay attention to their vitamin D levels.
Writing in the health section of the Today Show website, nutrition and health editor Joy Bauer gives some good, basic information about the vitamin and how to make sure you’re getting enough of it.
Regular exposure to sunlight allows your body to make its own vitamin D. All you need is about 15 minutes of direct sun, a few times a week. However, you should use common sense and limit your exposure to prevent sunburn.
In addition to sunlight, you can also get vitamin D from certain foods. These include fish such as mackerel, salmon, and sardines, as well as shrimp. Skim milk and fortified yogurts are good, too, as are fortified cereals. Shiitake mushrooms are also very high in vitamin D.
However, since food sources are limited, it might be a good idea to consider a supplement. If you take one, be sure that it contains at least the Daily Value, which is 400 IU. Women taking extra calcium should get a brand that also includes vitamin D, preferably D3 (cholcaciferol, the most potent form.)
An article at DermNet NZ, a health Web site set up by the New Zealand Dermatological Society, stresses that sunlight is the best way to get vitamin D without risking overdose. Your body will not make more of the vitamin than it needs, so there is a natural safeguard against getting too much of it that way. If you are taking a supplement, it is possible to get an overdose of the vitamin, which can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. An overdose of vitamin D can also raise your blood calcium level, sometimes causing confusion and heart rhythm abnormalities. It should be stressed that people taking vitamin D supplements should never exceed the recommended dosage.
The information in this article is not intended as a substitute for a doctor’s advice. Always consult your doctor when considering dietary changes, supplements, etc.
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