As if you needed another reason to make fitness your New Year's resolution: Two recent mortality studies have produced evidence that exercise - even light activity such as vacuuming or walking the dog - is even healthier than previously believed.
The studies are among the first wave of epidemiological papers based on objective measures of physical activity rather than self-reported responses. As such, they are considered more accurate.
The new studies were done by researchers at Harvard University and the renowned Karolinska Institute in Stockholm. They found that the most active subjects had a 50 percent to 70 percent decline in mortality during a defined follow-up period compared with the most sedentary participants. Previous self-report research had pegged this benefit at about 20 percent to 35 percent.
"We were somewhat surprised by the strong association between light activity and mortality," said Ing-Mari Dohrn, first author of the Swedish paper. "It was a strong factor for reductions in cancer and cardiovascular deaths, as well as for all-cause mortality."
Said an independent expert not connected to the new research, Francisco Lopez-Jimenez, "Both papers show very important findings. When we assess the protective effects of physical activity and exercise using objective methods, the benefit is larger than we had thought."
Lopez-Jimenez is chairman of the preventive cardiology division at the Mayo Clinic in Rochester, Minn., where he's also research director of the Dan Abraham Healthy Living Center.
Diet and exercise studies long have relied on self-reporting, which is notoriously inaccurate. Asked how much they eat or exercise, respondents reply in the expected direction. They under-report their food consumption and over-report their exercise habits.
The situation has improved for exercise epidemiologists, though, thanks to the development of lightweight, wearable accelerometers (think Fitbit). These allow scientists to collect objective activity data - such as how much they sit, how much they move - on large numbers of people.
I-Min Lee and her Harvard colleagues mailed accelerometers to more than 16,000 U.S. women, who wore them for 15 hours a day on four or more days. The researchers followed the women for an average of 2.3 years to determine their mortality data. The Swedes gave similar devices to 851 subjects, including almost 400 men, who wore them for 14 or more hours on four or more days. These subjects were tracked for 14.2 years.
In other words, one trial observed an impressively large number of subjects, while the other monitored its subjects for an impressive number of follow-up years. Although differing slightly on some methods and outcomes, the studies agreed on the most important results. Both concluded that subjects who moved a lot enjoyed a substantial longevity benefit over those who moved little.
"What's new and important is the strength of the association we discovered with the more precise measurements," said Lee, an exercise epidemiologist. "Our most active women had a 60 to 70 percent decline in mortality, which compares favorably to the 50 percent difference you would see between non-smokers and smokers. This is why the public should pay more attention to being physically active."
In addition, the Swedish team found that individuals who sit fewer than six hours a day have a 66 percent lower mortality risk than those who sit more than 10 hours a day.
Though working with different populations in different countries, both studies reported remarkably similar measurements for time sitting, time in light activity (i.e., folding the laundry, walking slowly, etc.), and time in moderate-to-vigorous activity (vacuuming, walking briskly or playing sports). Both Americans and Swedes appear to spend an average of 500 minutes a day sitting, 350 minutes in light activity and 30 minutes in moderate to vigorous activity.
Few adults engage in a lot of moderate to vigorous activity, but those minutes give a big boost to health and longevity. "The message should remain, as it has been, that 30 minutes or more of moderate-to-vigorous activity daily can reduce risk of death by 50 percent," Dohrn said.
Although the two studies tracked individuals in their late 60s to early 70s, both research teams believe the basic results would hold true for individuals several decades younger. "If anything, previous work based on self-reports indicated that the benefits are somewhat larger among younger subjects," Lee noted.
Most important, both studies showed that all physical activity improves health status. You don't have to play basketball for an hour or run 3 miles. You simply have to move your body forward, upward or side to side, as when washing the windows. (Despite their current popularity, standing desks don't add much to your movement count, not if you're standing still. You'd need to be walking on a treadmill.)
Both papers followed mortality rates first, because mortality allows for a simple yes/no outcome measure. But both teams are investigating other outcomes and believe their activity findings will apply to chronic-disease illnesses, such as obesity, diabetes and high blood pressure, that afflict so many. According to some reports, the economic cost of obesity in the U.S. is approaching $200 billion per year.
"We only examined mortality in the present study," Lee said, "but I want to emphasize that light intensity activity may be helpful for outcomes like daily functioning, mental well-being, good quality of life and so on."
Added Dohrn: "We are currently analyzing our data for chronic disease associations. We believe the important message should be that every little bit of physical activity is helpful. When you are doing housework or walking around instead of sitting, you are improving your health."