Older women who engage in more physical activity at higher intensities could cause a drastic drop in their risk of dying, says a new Harvard study published in the American Heart Association's journal Circulation. High levels of activity reduced the risk of dying by 70 percent.

Previous studies, which counted on volunteers reporting their activity levels, showed that active people have about 20 percent to 30 percent lower death rates compared to their least active counterparts.

Participants in the new study used a wearable device called a triaxial accelerometer, which allows for more precise measurements.

"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 the study's first author I-Min Lee, a professor of medicine and epidemiology at Harvard University's medical and public health schools in Boston, Massachusetts.

Data were analyzed from 16,741 participants whose average age was 72. During an average follow-up of approximately two-and-a-half years, 207 women died.

Researchers found that moderate to vigorous intensity physical activity (such as brisk walking) was associated with roughly a 60 percent to 70 percent lower risk of death among the most active women, compared to the least active.

Lighter activities, such as housework and the type of slow walking associated with window shopping, wasn't associated with death risk. But, researchers stressed that their findings do not mean light activity isn't beneficial for other health outcomes not studied here.

A recent study published in the American Journal of Psychiatry found that regular exercise — even if for only one hour a week — can help prevent depression. The study found that even small amounts of exercise, regardless of intensity, can protect against depression. Benefits were accrued regardless of age or gender.

Another study concluded that doctors should be prescribing more exercise for common chronic problems, including knee osteoarthritis, heart disease, diabetes, and chronic obstructive pulmonary disease. The review in CMAJ (Canadian Medical Journal Association) says exercise is often overlooked as a treatment.

Part of the reason doctors don't prescribe exercise is that they simply don't understand how effective exercise can be, and haven't a clue how to advise patients.

"Many doctors and their patients aren't aware that exercise is a treatment for these chronic conditions and can provide as much benefit as drugs or surgery, and typically with fewer harms," said the study's lead author Dr. Tammy Hoffmann of Bond University, Australia.