By Amy Norton

NEW YORK (Reuters Health) - People who want to forestall heart disease and diabetes may do better by choosing antioxidant-rich foods instead of antioxidant supplements, a new study suggests.

Researchers found that among more than 5,200 middle-aged adults, antioxidant supplements had no effect on the risk of developing metabolic syndrome over seven-plus years.

Metabolic syndrome refers to a collection of risk factors for type 2 diabetes, heart disease and stroke -- including high blood pressure, abdominal obesity, low levels of "good" HDL cholesterol, elevated triglycerides and high blood sugar. The condition is diagnosed when a person has at least three of those risk factors.

The current findings, reported in the American Journal of Clinical Nutrition, suggest that taking antioxidants in capsule form may not thwart metabolic syndrome.

On the other hand, men and women who began the study with relatively high blood levels of certain antioxidants -- particularly vitamin C and beta-carotene -- were less likely than those with lower levels to develop metabolic syndrome.

The implication is that even though antioxidant supplements might not cut the risk of metabolic syndrome, antioxidant-rich foods just might, according to the researchers, led by Dr. Sebastien Czernichow of the French national research institute INSERM, in Paris.

Blood levels of vitamin C and beta-carotene are "rather good surrogate markers" of people's fruit and vegetable intake, Czernichow told Reuters Health in an email.

"This reinforces the guidelines for an adequate intake of this food group and goes against the regular use of antioxidant pills," he said.

The study included 5,220 adults with an average age of 49 who were randomly assigned to take either a mix of vitamins C and E, beta- carotene, selenium and zinc in capsule form or inactive placebo capsules.

After an average of 7.5 years, 263 study participants had been diagnosed with metabolic syndrome. There was no significant difference in risk between the supplement and placebo groups.

There were differences, though, when the researchers looked at participants' antioxidant blood levels at the study's outset. The one-third with the highest vitamin C levels had about half the risk of metabolic syndrome as those with the lowest levels.

Similarly, the third with the highest beta-carotene levels had only one-third of the risk of metabolic syndrome as those with the lowest beta-carotene concentrations.

In contrast, higher zinc levels in the blood were linked to an increased risk of metabolic syndrome. It's not clear why this is, but the researchers speculate that high zinc levels might, in some people, reflect heavy consumption of red meat -- one of the prime food sources of the mineral.

Good food sources of vitamin C include citrus fruits, strawberries and cantaloupe, and vegetables such as red peppers, broccoli and tomatoes.

Beta-carotene, which is converted in the body into vitamin A, is found in foods such as carrots and sweet potatoes, and leafy greens like spinach and kale.

SOURCE: American Journal of Clinical Nutrition, August 2009.

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