Research reveals dangerous midlife switch of ditching activity to sit still

The study, published today in the American Journal of Epidemiology, is the first time age-related physical activity changes, from inactivity to vigorous exercise, have been examined at such a large scale across midlife. People in the study who were between the ages of 38 and 50 dropped their activity rates over the next decade by an average of a half an hour a day and replaced it with doing something sedentary.

"We know higher intensity physical activity tends to decline with age. But these findings show just how much even gentle forms of activity that are part of daily routines, like casual walking, slip in midlife, which doesn't bode at all well for future health and should serve as a wake-up call to us all," said first and corresponding author Kelley Pettee Gabriel, Ph.D., M.S., associate professor of epidemiology, human genetics and environmental sciences at the Michael & Susan Dell Center for Healthy Living at the UTHealth School of Public Health Austin campus.

Investigators were able to draw the conclusions using data from the Coronary Artery Risk Development in Young Adults Study, also known as CARDIA, which started following 5,115 participants between ages 18 to 30 more than 30 years ago, measuring their activity levels with an accelerometer, or activity monitor, that is similar to a pedometer.

These decreases of physical activity over a 10-year period in middle age were observed in both men and women. However, the decline was steepest among black men who typically started being the most active but reduced their activity levels by nearly one hour daily. Black women began as the least active, and continued to have the lowest physical activity levels 10 years later.

"Our next step is to determine what is causing these changes towards a more inactive daily routine. It could be that during midlife people become busy with their jobs and taking care of children and aging parents. Or, they may be experiencing more difficulty moving around because of aching joints, for instance," Gabriel said. "What's clear is that these trends are happening at a time when people face increased risk of disease and disability. Yet, compared to older adulthood, they're also potentially in a better position to introduce more physical activity back into their daily routine, particularly as they retire."

National guidelines recommend at least two and a half hours of moderate intensity activity per week, or an hour and 15 minutes of vigorous intensity activity per week, or an equivalent combination of moderate and vigorous intensity activity. They also discourage prolonged sedentary time.

Physical activity is advised to help manage conditions including obesity, high blood pressure and type 2 diabetes. There's also a growing body of evidence demonstrating the health benefits for older adults of undertaking light intensity physical activity, such as going for a gentle stroll or doing household chores. Such evidence led to the 2018 Physical Activity Guidelines Advisory Committee recommendation that additional research is needed for further understanding.

"Given the findings of our study and others, the health consequences of age-related switches from time spent in light intensity physical activity to sedentary pursuits merit serious consideration and could pave the way for future physical activity guidelines to set targets in these important areas," said Gabriel. "Making relatively small lifestyle changes, and taking advantage of missed opportunities to be physically active could have a crucial bearing on how people are setting themselves up for being more resilient during older adulthood. Simple changes all add up, like walking to the corner coffee shop, parking further away from the store entrance or taking the stairs rather than the escalator."

Barbara Sternfeld, Ph.D., emeritus research scientist of Kaiser Permanente Northern California, was senior author of the study, which was funded by the National Heart, Lung, and Blood Institute and the National Institute on Aging, both part of the National Institutes of Health.

The vision of UTHealth School of Public Health is to improve the health of the population through prevention, better health outcomes and a trained population health workforce.