May 31, 2007 (Insidermedicine) Forty minutes of aerobic exercise done three times a week produces a small but real increase in high density lipoprotein (HDL), otherwise known as "good cholesterol," according to a study published in the May 28 issue of the Archives of Internal Medicine.

Increased HDL is good, since it aids in the removal of an artery-clogging form of cholesterol called low-density cholesterol. The build-up of low-density cholesterol along arterial walls – a process called plaque formation – causes atherosclerosis ("hardening of the ateries"), which can make the heart work harder to pump blood through narowed arteries. Furthermore, bits of plaque can break away and subsequently block a narrower portion of an artery, reducing or completely stopping blood flow. The consequences – heart attacks, "mini strokes", and full-blown strokes – afflict over 5 million North Americans each year.

While the benefits of exercise on cholesterol levels have been long-known, the amount of exercise needed to produce the benefits is less clear. As well, it is unclear whether more frequent but shorter exercise sessions are any better than a few, more prolonged sessions.

Hirohito Sone of Tokyo's Ochanomizu University and colleagues analyzed studies that had been published from 1966–2005 and identified 35 trials with over 1,000 young adult to elderly participants. On average, the participants huffed and puffed through about 4 aerobic exercise sessions a week, with each session lasting a bit over 40 minutes. Aerobic exercise was considered to be rhythmic, repeated movements of certain muscles for at least 15 minutes – typical exercises included walking, jogging, bicycling, and swimming.

The statistical analysis revealed the length of exercise was most strongly linked to the boosted HDL levels, with at least 2 hours of exercise per week (about 900 calories worth of work) being necessary to bump up HDL. This is longer than the 30 minutes per week currently recommended by United States Centers for Disease Control and Prevention and the American College of Sports Medicine.

The intensity of exercise and the frequency of exercise were not associated with increased HDL.

"This suggests 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," concluded the researchers.

They added that a healthy diet is also a wise strategy, especially in obese people for whom exercise along might not be sufficient to ratchet up the level of HDL

The take-home message from the study is that several exercise sessions a week is a good thing for "good cholesterol."

Reporting for Insidermedicine, I'm Dr. Petra Joller.