Harvard Health Letter

Let's talk to an expert

Dr. I-Min Lee is an associate professor of medicine at Harvard Medical School and an expert on the epidemiology of physical activity and health. Dr. Lee served on the federal government's Physical Activity Guidelines Advisory Committee, the 13-member group that examined the scientific evidence that lay the groundwork for new government physical activity guidelines due out in October 2008.

How much exercise should we be getting?

Well, that was a primary focus of the committee — reviewing what scientific studies tell us about the amount of physical activity we should get. In general, we agreed that the available evidence supports previous recommendations from various expert groups: get at least 30 minutes of moderate-intensity physical activity, like brisk walking, at least five days of the week, or 20 minutes of vigorous activity, like jogging, at least three. Or get a combination of moderate- and vigorous-intensity activities that satisfies the minimum of either regimen. This level of activity has been shown in many studies to delay mortality, decrease the risk of many chronic diseases, and improve overall health.

But the committee also concluded that recent data suggest that even an hour of physical activity a week — just an hour total — causes heart disease and mortality rates to start going down; with additional activity, additional declines are seen.

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