Not a week goes by, it seems, without a study touting the health and/or life-extending benefits of walking.
Just last month, researchers with the American Cancer Society (ACS) reported that older adults who walked an average of only an hour a week — even at a slow pace — had a 20 percent lower risk of premature death than those who did no exercise.
Now along comes a new study, published Monday in the journal Circulation. It, too, sings the praises of walking. Yet it seems to contradict the results reported in the ACS study — or, at least, the one about the benefits of slow walking.
The Circulation study found that older women who engaged in regular moderate- to vigorous-intensity physical activity — such as brisk walking — were up to 70 percent less likely to die prematurely during a four-year period than their peers who didn’t get as much exercise.
The study differs from most previous ones because it didn’t rely only on the participants’ answers to questionnaires about their activity levels. Instead, the women were given wearable devices known as triaxial accelerometers, which are able to measure not just the amount, but also the level of physical activity.
“The fact [that] physical activity lowers mortality rate is nothing new — we have many studies showing this,” said I-Min Lee, the study’s lead author and an epidemiologist at Brigham and Women’s Hospital, in a released statement. “However, previous studies have primarily relied on self-reported physical activity, and self-reports tend to be imprecise.”
Those self-report studies — like the ACS one — have tended to show that physical activity is associated with up to a 30 percent reduction in mortality rates.
For the current study, Lee and her colleagues used data collected from more than 16,741 women in the ongoing Women’s Health Study. The average age of the women at the start of the current study was 72. Most were relatively healthy, and all could walk unassisted outside their home.
At the beginning of the study, the women were given a triaxial accelerometer to wear for 10 hours or more for at least four out of seven days. These devices “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 Lee.
Based on the data from the devices, the women were divided into four activity-level groups. About half of the women spent at least 28 minutes in moderate- to vigorous-intensity physical activity on an average day, or around 196 minutes a week.
Current public health guidelines recommend that adults engage in at least 150 minutes of moderate-intensity physical activity, or 75 minutes of vigorous-intensity physical activity, each week.
All the women were followed for an average of 2.3 years. During that period, 207 of the women died.
When the researchers compared the most active group of women in the study to the least active group, two key findings emerged:
- Regular moderate- to vigorous-intensity exercise — the equivalent of brisk walking or greater — was associated with about a 60 percent to 70 percent lower risk of death.
- Light-intensity activity — say, housework and slow walking (such as window-shopping in a mall) — was not independently associated with a reduced risk of death.
These findings held even when the researchers excluded from their analysis women who had been diagnosed with heart disease or cancer or who had rated their health as fair or poor at the start of the study. The findings also held when all deaths that occurred during the study’s first year were discounted.
Limitations and implications
This was an observational study, so it doesn’t prove that exercise can reduce the risk of premature death. Other factors, not adjusted for by the researchers, might explain the results.
The study also followed the participants for a relatively short time.
In addition, as Lee and her colleagues point out, only 63 percent of eligible women in the Women’s Health Study participated in their study, a factor that may limit the generalizability of the findings. And the fact that it included only women may limit its relevance for men.
Still, the study “adds meaningfully to existing data because of its large sample size, use of triaxial accelerometer data, and investigation of a clinical outcome,” Lee and her colleagues write in their paper.
The study also “supports current guidelines for physical activity, such as those from the federal government and the American Heart Association that emphasize moderate-intensity physical activity,” said Lee in a second released statement.
“We hope to continue this study in the future to examine other health outcomes, and particularly to investigate the details of how much and what kinds of activity are healthful,” she added. “What is irrefutable is the fact that physical activity is good for your health.”
FMI: You can download and read the study in full on Circulation’s website.