Exercise Gives HDLs a Modest Boost

TOKYO, May 29 -- A regular aerobic exercise program of at least two hours a week produced a small but significant increase in HDLs, according to a meta-analysis.

The rise was 2.53 mg/dL (95% confidence interval 1.36-3.70 mg/dL P<0.001), Hirohito Sone, M.D., Ph.D., of Ochanomizu University here, and colleagues, reported in the May 28 issue of the Archives of Internal Medicine.

Exercise duration per session of about 40 minutes for a total of 120 minutes a week was the most important element in the exercise prescription, suggesting that a minimum exercise volume is necessary to raise HDL levels, they found.

A Medline search for randomized controlled trials from 1966 to 2005 examining the effect of exercise training on HDL levels produced 25 articles (35 trials) with 1,404 participants, age range 23 to 75. Aerobic exercise was defined as rhythmic and repeated movements of the same large-muscle groups (walking, bicycling, and continuous swimming) for at least 15 minutes.

The exercise groups worked out for an average of 3.7 sessions a week at an average of 40.5 minutes each, burning an average of 1,019 calories a week.

Univariate analysis showed that exercise duration was the strongest predictor of the mean difference in HDL change. Each 10-minute increase in exercise duration corresponded to an approximately 1.4 mg/dL increase in HDL, when the duration ranged from 23 to 74 minutes per session.

The minimum amount of weekly exercise that appeared necessary to increase an HDL level was estimated to be 900 kcal of energy expenditure a week or 120 minutes of exercise a week.

In contrast, there was no significant association between exercise frequency or intensity, the investigators found.

"This suggests," they said, "that increasing time per session is better than doing multiple brief exercise sessions when time for exercise is limited, as is the case for many people."

Although the CDC and the American College of Sports Medicine recommend about 30 minutes of moderate-intensity physical activity, such as brisk walking on most days, this study suggests that a longer duration per session of continuous exercise than the recommendation is necessary for a significant increase in HDLs, the researchers said.

Exercise was more effective in participants with initially high total cholesterol levels or low body mass index. Multiple meta-regression analyses showed that those with a body mass index less than 28 and total cholesterol level of 220 mg/dL or more had an approximately 2.1-mg/dL larger increase in HDL levels than those with a body mass index of 28 or more and total cholesterol less than 220 mg/dL, the investigators said.

The researchers speculated that lack of improvement in obese patients is difficult through exercise alone, and that reducing body weight along with exercise, is more effective.

According to a previous observational study, every 1-mg/dL increase in HDL-C level was associated with a 2% to 3% decreased risk of cardiovascular disease in men and women, respectively, the authors said. "If this observation were applied to our results, the increase in HDL-C level by exercise, determined by this analysis would, by a rough estimate, result in a cardiovascular disease risk reduced by approximately 5.1% in men and 7.6% in women."

Nevertheless, they said, that although this is potentially of substantial importance in public health, the effect of reducing cardiovascular risk by increasing HDL level might be smaller than that obtained through medication, such as fibrates or niacin.

Study limitations included the fact that meta-analysis was confined to published studies, which might have produced publication bias. Also, most trials did not provide data on the period from the last exercise session to the measurement, so that exercise might have raised HDL levels as an acute effect.

In addition, most of the trials did not include data on alcohol intake, a possible influence on the results.

The researchers suggested the need for further studies comparing expected reductions of cardiovascular risk when HDL-C is increased through exercise, ethnic and sexual differences in these increases, and a review of the effect of resistance training on HDLs.