15 minutes daily exercise may be reasonable target in older adults

"Age is not an excuse to do no exercise," said Dr Hupin. "It is well established that regular physical activity has a better overall effect on health than any medical treatment. But less than half of older adults achieve the recommended minimum of 150 minutes moderate intensity or 75 minutes vigorous intensity exercise each week."

He continued: "We wanted to find out whether lower levels of exercise could be beneficial and even reduce mortality in older adults."

The authors studied two cohorts. A French cohort of 1011 subjects aged 65 in 2001 was followed over a period of 12 years. An international cohort of 122 417 subjects aged 60 was included from a systematic review and meta-analysis using PubMed and Embase databases, with a mean follow up of 10 years.

Physical activity was measured in Metabolic Equivalent of Task (MET) minutes per week, which refers to the amount of energy (calories) expended per minute of physical activity. One MET minute per week is equal to the amount of energy expended just sitting. The number of MET minutes an individual clocks up every week depends on the intensity of physical activity. For example, moderate intensity activity ranges between 3 and 5.9 MET minutes while vigorous intensity activity is classified as 6 or more.

The recommended levels of exercise equate to between 500 and 1000 MET minutes every week. The authors looked at the associated risk of death for four categories of weekly physical activity in MET minutes, defined as inactive (reference for comparison), low (1-499), medium (500-999) or high (over 1000).

During the follow up there were 88 (9%) and 18 122 (15%) deaths in the French and international cohorts, respectively. The risk of death reduced in a dose response relationship as the level of exercise increased. Compared to those who were inactive, older adults with low, medium and high activity levels had a 22%, 28% and 35% lower risk of death, respectively.

Dr Hupin said: "These two studies show that the more physical activity older adults do, the greater the health benefit. The biggest jump in benefit was achieved at the low level of exercise, with the medium and high levels bringing smaller increments of benefit."

"We found that the low level of activity, which is half the recommended amount, was associated with a 22% reduced risk of death in older adults compared with those who were inactive," said Dr Hupin. "This level of activity equates to a 15 minute brisk walk each day."

He concluded: "We think that older adults should progressively increase physical activity in their daily lives rather than dramatically changing their habits to meet recommendations. Fifteen minutes a day could be a reasonable target for older adults. Small increases in physical activity may enable some older adults to incorporate more moderate activity and get closer to the recommended 150 minutes per week."