Greater health benefit from exercise than previously reported

Lack of exercise or physical activity is estimated to cause as many deaths each year as smoking, according to a new study led by investigators at Harvard-affiliated Brigham and Women’s Hospital (BWH).

Current guidelines recommend at least 150 minutes a week of moderate-intensity physical activity, or 75 minutes a week of vigorous-intensity aerobic physical activity (or a combination of the two), and muscle-strengthening exercises two or more days a week.

The study, which was published Monday in Circulation, investigated women’s physical activity measured over seven days by a wearable device called a triaxial accelerometer, and found that more physical activity and higher intensities of physical activity could decrease the risk of death in older women from any cause. Moderate to vigorous intensity physical activity (e.g., brisk walking) was associated with 60–70 percent lower risk of death at the end of the four-year study among the most active women, compared to the least active.

“The fact the physical activity lowers mortality rate is nothing new — we have many studies showing this. However, previous studies have primarily relied on self-reported physical activity, and self-reports tend to be imprecise. Based on these self-report studies, we know that physical activity is associated with a 20–30 percent reduction in mortality rates, comparing the most with the least active. Using device-measured physical activity in the present study, we observed a 60–70 percent risk reduction, larger than previously estimated from self-report studies. For context, nonsmokers have about a 50 percent reduction, compared with smokers,” said Harvard Medical School Professor I-Min Lee, an associate epidemiologist at Brigham and Women’s Hospital and first author of the study.

“This study supports current guidelines for physical activity, such as those from the federal government and the American Heart Association, that emphasize moderate-intensity physical activity. It also adds to existing evidence that can inform upcoming physical activity guidelines over time.”

This is one of the first studies to investigate physical activity, and a clinical outcome, using the newer-generation triaxial wearable devices, which have increased sensitivity to recognize physical activity and are capable of more precise measurements than the previously used uniaxial devices, or studies relying on self-reports only.

“We used devices to better measure not only higher-intensity physical activities, but also lower-intensity activities and sedentary behavior, which has become of great interest in the last few years,” said Lee.

Data were analyzed from 16,741 participants (average age 72) from the Women’s Health Study who wore the device for at least 10 hours a day, on at least four out of seven days.

Light physical activity, such as slow walking, was not associated with lower death rate during the study. Researchers note that light activity may be beneficial for other health outcomes not reported in this paper. Researchers are continuing this study to examine other health outcomes and to examine details of how much and what kinds of activity are healthful.

The study is supported by National Institutes of Health grants CA154647, CA047988, CA182913, HL043851, HL080467, and HL099355.