Older women who engage in moderate to vigorous physical activity — such as often taking brisk walks — may be adding years to their lives when compared with women who are not very active.
This was the main finding of a large study — by researchers from Brigham and Women's Hospital in Boston, MA — that measured physical activity in older women as they wore sensitive activity trackers and then followed them for up to 4 years.
"Physical inactivity is estimated to cause as many deaths globally each year as smoking," note the researchers in a report on the study that was published recently in the journal Circulation.
In the United States, the current federal guidelines for improving health through physical activity recommend that per week, adults should undertake 150 minutes of "moderate-intensity aerobic physical activity," 75 minutes of "vigorous-intensity aerobic physical activity," or an "equivalent combination" of the two.
The federal guidelines give brisk walking and tennis as examples of moderate-intensity activity, and jogging and swimming as examples of vigorous-intensity activity.
In addition, they advise that the recommended aerobic activity should be accompanied by muscle-strengthening exercises, such as with weights or resistance bands, at least twice per week.
Risk reduction much larger than first thought
The study found that there was a strong relationship between the amount of exercise recorded on the women's activity trackers and a lower risk of death from all causes during the follow-up period.
The researchers explain that although evidence of such a relationship is not new, the size of the risk reduction that they found is much greater than that reported in the wealth of older research that led to the guidelines' publication.
They found that the most active 25 percent of the women had a 60–70 percent lower risk of dying over the follow-up period than the least active 25 percent.
The new study is one of the first to use data from a new generation of wearable devices known as "triaxial accelerometers" and relate the measurements to a clinical outcome — which, in this case, was death from all causes.
In previous studies that have examined the same relationship, the activity data were gleaned from participants' own self-reports or less sophisticated "uniaxial devices." Analyses based on these have estimated a much smaller risk reduction of 20–30 percent.
"The fact the physical activity lowers mortality rate is nothing new," says first study author Dr. I-Min Lee, adding that "we have many studies showing this. However, previous studies have primarily relied on self-reported physical activity, and self-reports tend to be imprecise."
More sensitive, accurate activity measures
The more advanced devices used in the new study are better at recognizing physical activity and can measure it more precisely. For example, they can differentiate low levels of physical activity — such as slow walking — from just sitting or sedentary behavior, which scientists have become more interested in lately.
The team notes that the finding of a 60–70 percent reduction in risk puts the effect of physical activity on a par with that of not smoking; non-smokers have a 50 percent lower risk of early death compared with those who do smoke.
For the new study, the researchers analyzed records from tens of thousands of women taking part in the Women's Health Study.
The analysis only included women who had worn the triaxial accelerometers that had been mailed to them for a minimum of 10 hours per day on at least 4 days out of the 7 designated to them. The total number of participants included was 16,741, and their average age was 72 years.
The authors note that 207 of the women died over an average follow-up period of 2.3 years. The deaths were confirmed using death certificates, medical records, and the National Death Index.
Light activity not tied to reduced death risk
As well as finding a 60–70 percent lower risk of death in the most active women, the researchers found no link between reduced risk of death and light-intensity physical activity — such as slow walking or window shopping in malls — or sedentary behavior.
However, they point out that this does not mean that light-intensity physical activity has no value; it may well benefit other areas of health that they did not measure in this study.
The researchers decided to study older women because there are gaps in the evidence relating to this group. Dr. Lee says, "Younger people in their 20s and 30s generally can participate in vigorous-intensity activities, such as running or playing basketbal."
However, older people might find it difficult, if not impossible, to exercise at a vigorous- or even a moderate-intensity level. So, the team wanted to see whether there were any benefits from light-intensity physical activities that older people are more likely to engage in.
The researchers note that the participants that they studied were mainly white women in good health, and that their findings may not apply to other groups in the general population.
In the meantime, they are continuing with the study in order to compare physical activity measures with other health outcomes. They also wish to estimate the effects of the amount and types of exercise on health.
"This study supports current guidelines for physical activity, such as those from the federal government and the American Heart Association [AHA], that emphasize moderate-intensity physical activity. It also adds to existing evidence that can inform upcoming physical activity guidelines over time."
Dr. I-Min Lee