Vitamins, Exercise & Diabetes

by Barbara C. Neff

Exercising regularly and popping vitamins have long been regarded as two of the surest and easiest tools for improving our health. Researchers, however, recently found that antioxidant supplements like vitamins C and E may preempt some of the most valuable health benefits of exercise, particularly for those who exercise to ward off or manage Type-2 diabetes.

Proponents claim that antioxidants combat oxidative stress or damage caused by free radicals that attack the body's tissues, making them more vulnerable to cancer, viruses and infection. "Whenever there's damage to a cell," says Cami Morgan, a dietitian and diabetes educator with the DuPage Medical Group, "antioxidants are supposed to decrease that damage." The American Heart Association estimates that up to 30 percent of Americans take some form of antioxidant supplement.

Many of these individuals also engage in regular exercise. Such exercise has been shown to reduce the risk of premature death, coronary heart disease, stroke, hypertension, depression, certain types of cancer and diabetes. Brenda Jagatic, a diabetes educator at the Edward Diabetes Center, says exercise is always recommended for those who battle Type-2 diabetes or suffer from pre-diabetes.

Type-2 diabetes develops when the body becomes insulin resistant, leading to high blood glucose (or "blood sugar"). "The pancreas adapts to the stress by making more insulin to compensate," Jagatic says, "but, at some point in the disease process, the pancreas burns out and starts to make less insulin."

As researchers noted in a study published in May in the Proceedings of the National Academy of Sciences, exercise increases insulin sensitivity and improves glucose metabolism. Exercise also produces oxidative stress from free radicals, though. According to the researchers, antioxidant supplements may block the oxidative stress but also the beneficial effects of exercise on insulin sensitivity.

The researchers came to this conclusion after looking at the effect of exercise on insulin resistance in 39 young men. About half of the men took supplemental vitamins C and E. Those taking the vitamin supplements saw no significant improvement in their insulin sensitivity, while the men not taking the vitamins experienced an increase in both free radicals and insulin sensitivity.

"Exercise is a proven way to improve insulin action and reduce diabetes risk, but clearly this beneficial effect can be largely blocked by taking these very commonly used vitamin supplements," says Dr. C. Ronald Kahn, a researcher on the study with the Joslin Diabetes Center and Harvard Medical School. "We need larger studies to fully asses this effect, but, in the meantime, individuals at risk for diabetes, and maybe even some with Type-2 diabetes itself, need to think carefully about the use of these vitamin supplements, especially if they exercise regularly to improve their health."

Morgan says that she advises patients to get their antioxidants from whole foods and avoid "mega" doses of supplements, which could do more harm than good. She points out that the study suggested fruits and vegetables may have health-promoting effects despite their antioxidant content, possibly due to other bio-active compounds.

"If you get antioxidants from those foods, there are a lot of those other bio-active compounds that may actually promote the antioxidants to work better," Morgan says. "If you're just taking it as a supplement, you may not be getting those other compounds, so it may not be working as well."

Jagatic takes a similar stance. "If patients want to take a supplement, I recommend they follow the instructions on the label, but we always tell them their whole foods are the most important thing," she says. "You can't just take supplements and not worry about the diet."

To make the most of your diet, Morgan recommends a colorful plate, featuring a mix of orange, green, blue and yellow foods. "Then you'll know you're getting all of the antioxidants, vitamins and minerals that you need."