Although reduced physical activity during the day is widely seen as a harbinger of mortality in older people, fragmentation of physical activity — spreading daily activity across more episodes of brief activity — may be an earlier indicator of mortality risk than total amount of daily activity, according to a new study from scientists at the Johns Hopkins Bloomberg School of Public Health.
The study, published October 2 in JAMA Network Open, used physical activity data collected using wearable monitors in 548 well-functioning older adults enrolled in the National Institute on Aging’s Baltimore Longitudinal Study of Aging. The scientists found that for this group of people during the period 2007 to 2017 there was no association between overall daily activity levels and greater mortality risk. However, there was an association between mortality risk and more fragmented physical activity.
Of the 548 participants studied, 487 were alive at the end of 2017, and 61 were deceased. The living participants engaged in an average of 5.7 hours of activity per day, compared to 4.7 hours for those who later died. But after accounting for confounding factors such as age, sex, race, body mass index, and existing illnesses, the researchers found that total physical activity overall was too weakly associated with mortality risk to reach statistical significance.
Not so for activity fragmentation. The researchers found that for each 10 percent higher activity fragmentation a 49 percent increase in the risk of mortality.
Dr. Amal Wanigatunga, assistant scientist in the Bloomberg School’s department of epidemiology, is the paper’s lead author. Dr. Jennifer Schrack, associate professor, also in the department of epidemiology, is senior author.Friday Letter Submission, Publish on October 04