Keeping your "good" cholesterol (HDL) high – with plenty of exercise and a healthy body weight – is not only important for cardiovascular health, but could also benefit lung health, according to a new study at Cornell University. Nutritional epidemiologists here find that HDL is linked to healthy lungs, though they stress that more research is needed to understand if this is a cause-and-effect relation.

"Previous studies that have looked at cholesterol and pulmonary disease reported inconsistent findings, but they all looked at total cholesterol, which may confuse the issue," says Patricia Cassano, an epidemiologist and assistant professor in the Division of Nutritional Sciences at Cornell. "Our study, unlike any others we know of, examined the association of the high-density and low-density lipoproteins [HDL and LDL] with lung function." The study is published in a recent issue of the American Journal of Epidemiology (Vol. 155, No. 9, 2002).

In an analysis of the 1988-1994 National Health and Nutritional Examination Survey of 18,162 randomly selected adults in the United States, Cassano and co-authors Dominic J. Cirillo and Yuri Agrawal, both former research assistants at Cornell, explored how HDL and LDL cholesterol are associated with lung function in healthy people. HDL and LDL, often referred to as "good" and "bad" cholesterol, have well-known and differing effects on heart disease.

Lung function was measured by a spirometer, which indicates the health of the lungs by showing the degree of airflow limitation. The measurements (including forced expiratory volume in the first second) are, says Cassano, excellent predictors of chronic obstructive pulmonary disease (COPD), the fourth leading cause of death and third leading cause of disability in the United States. Deaths from COPD, which includes emphysema and chronic bronchitis, have jumped more than 165 percent over the past three decades.

About 85 percent of people with COPD develop the disease because of cigarette smoking. However, only about 15 percent of smokers develop COPD, and researchers are interested in factors that could help to identify susceptible smokers and predict risk in nonsmokers.Several years ago Cassano reported that antioxidants seemed to play an important role in protecting lung function and might even help prevent asthma, emphysema and chronic bronchitis (American Journal of Epidemiology Vol. 151, No. 10, 2000). Antioxidants are substances, such as beta carotene and selenium, that work in different ways to protect cells from biochemical damage. Cassano's latest study controlled for factors such as antioxidant and smoking status, alcohol intake, body fat and exercise level.

Cassano says that previous studies suggested that exceptionally low total cholesterol was linked to an increased risk of cancer, respiratory disease and other non-cardiovascular causes of death. The new study did not support these previous findings, and suggested a different pattern, perhaps, in part, because it looked separately at the two sub-components of cholesterol:

• Total cholesterol had little or no association with lung function.
• Higher HDL was associated with better lung function.
• Lower LDL was associated with better lung function.

Although Cassano's cross-sectional study found that lower levels of LDL cholesterol were associated with better lung function, a recent large clinical trial found that lowering LDL levels with a statin drug had no effect on lung function. The large, randomized clinical trial provides more definitive information on cause and effect, Cassano says.

"Conflicting findings are common in science and help propel science forward," Cassano points out. "The newest clinical trial findings suggest that lowering LDL cholesterol has little or no effect on pulmonary function, but our findings on HDL, on the other hand, remain of interest. HDL may have a positive effect through its role in immune regulation as it has been shown to bind to bacterial toxins and to relieve inflammation, which may contribute to the prevention of lung-tissue damage. But it is too early to draw any conclusions, and further research is indicated."

Aside from potential benefits for lung health, increasing HDL levels is important for cardiovascular disease prevention. To boost HDL levels, the National Heart Lung and Blood Institute recommends maintaining a healthy weight, getting plenty of exercise and not smoking. Moderate alcohol intake also is linked to increasing HDL levels.

The study was supported in part by grants from the National Institutes of Health, the U.S. Department of Agriculture and Hatch Federal Formula Funds.