But men may not get the same benefit, according to another study. Both studies were presented this week at the American Thoracic Society international conference in New Orleans.
The risk reduction for women on vitamin E supplements was equal in people who smoked -- the primary risk factor for getting COPD -- and people who didn't, says Anne Hermetet Agler, a PhD candidate at Cornell University and lead author of the study involving women.
''We saw a 10% reduction in risk," she says. The women took 600 IU of vitamin E every other day. Of the effect, she says, "It is limited to just women."
Vitamin E, an antioxidant, has been looked at as a lung disease preventive because it is thought to protect against free radicals, molecules that damage cells and one of the proposed processes by which lung disease is thought to develop. But previous research has found little or no effects of antioxidants on lung outcomes, Agler says. And other research has found increasing vitamin E may slightly increase lung cancer risk and other ill effects.
More than 16 million Americans have COPD, also known as emphysema and chronic bronchitis, according to the National Lung Health Education Program.
Vitamin E and Women's COPD Risk
Agler and her co-researchers analyzed data that had already been gathered for the Women's Health Study. The long-term research effort ended in 2004 and focused on what effects aspirin and vitamin E had in the prevention of cardiovascular disease and cancer in nearly 40,000 women, age 45 and older.
During that study, women were randomly assigned to groups that took either 600 IU of vitamin E every other day, 100 milligrams of aspirin every other day, or placebo. None of the women had COPD at the start of the study.
During the nearly 10-year follow-up, there were 760 new reports of COPD in the vitamin E group and 846 in the placebo group, translating to a 10% risk reduction for the supplement group.
The effect held when Agler considered a number of other factors, including smoking status, age, and multivitamin use.
Even though the vitamin E reduced the overall risk of COPD in both smokers and nonsmokers, the current smokers were more than four times as likely as never smokers to get COPD, the researchers found.
Agler also looked at the effect of vitamin E on new diagnoses of asthma, but found little or no association.
Vitamin E and Men's COPD Risk
Men don't appear to get the same protection from vitamin E, according to study author Patricia Cassano, PhD, associate professor of nutritional epidemiology at Cornell University.
She and her colleagues looked at data from the SELECT Trial (Selenium and Vitamin E Cancer Prevention Trial), originally set up to look at the effects of those supplements on cancer.
More than 35,000 men participated, and their median age was 62.4 (half younger, half older). Some of the men took 400 IU of vitamin E a day, with or without 200 micrograms a day of selenium, and were compared to those taking placebo. They were followed for four to more than seven years.
Neither selenium nor vitamin E, alone or in combination, made a difference in preventing COPD, the researchers found, compared to placebo.
Vitamin E and the Gender Difference
Exactly why vitamin E reduced the COPD risk in women but not men is not known.
But Agler suggests that it might be related to the fact that cells in the lung are believed to take up vitamin E preferentially from HDL or "good" cholesterol" -- and that ''women tend to have higher HDL than men."
Vitamin E and COPD: Second Opinion
The COPD risk reduction of 10% found in women is termed "slight" by Chris Slatore, MD, an assistant professor of pulmonology at Oregon Health & Science University (OHSU) and the Portland VA Medical Center and an investigator at the OHSU Knight Cancer Institute. He was not involved in either study but reviewed the findings for WebMD.
Still, he says, the reduction is worthwhile enough to pursue the research.
In his own research, he has found that increasing vitamin E is associated with a slightly increased risk of lung cancer. "There might be a risk of vitamin E for lung cancer, and we definitely did not see a benefit as far as protecting from lung cancer," he says.
The results from the new women's study on vitamin E, he says, "wouldn't convince me that vitamin E reduces the risk of COPD enough to take it."
Vitamin E: How Much Is Enough?
For people aged 14 and older, the Recommended Dietary Allowance of RDA is 22.4 IU, with 1,500 IU a day considered a maximum safe level.
Nuts, seeds, vegetable oils, and green leafy vegetables are sources of vitamin E.
Besides acting as an antioxidant, vitamin E is involved in immune system functioning and signaling between cells and other processes in the body.