Brisk walking/physical activity of similar intensity may lower risk of death among older women

Lack of exercise or physical activity is estimated to cause as many deaths each year as smoking. 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.

A new study led by investigators at Brigham and Women's Hospital published in Circulation on November 6, 2017, investigated physical activity of women measured over seven days using 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, non-smokers have about a 50 percent reduction, compared with smokers," stated I-Min Lee, MBBS, ScD, 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," stated I-Min Lee, MBBS, ScD.

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.

Researchers found:

• More moderate to vigorous intensity physical activity (such as brisk walking) was associated with roughly a 60 percent to 70 percent lower risk of death at the end of the study among the most active women, compared to the least active.
• More light intensity activity (such as housework and slow walking - e.g., window shopping in a mall), or more sedentary behavior was not independently associated with death risk at the study's end. Researchers stressed this finding does not mean light activity isn't beneficial for other health outcomes not studied here.

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.