People who walk or jog for just a couple of hours each week are at lower risk of heart disease than those who don't exercise, suggests a new meta-analysis.
And among people already accustomed to exercise, those who go above and beyond on physical activity seem to have the best heart outcomes, said researchers who analysed past data on exercise and heart disease risks.
The authors of the new study, led by Dr Jacob Sattelmair, wanted to test the benefit of exercise on heart disease in relation to new federal guidelines.
United States guidelines from 2008 recommend 150 minutes of moderate exercise each week, or 30 minutes five days per week, as a minimum for health benefit. Twice that, the guidelines say, adds additional benefit.
The researchers collected data from nine past studies that asked participants how frequently they exercised, and for how long each time, and followed them for periods ranging from a few years to a couple of decades.
Those types of studies do have some limitations, the researchers noted. For example, they didn't all collect information on participants' diets, so it's hard to know if the heart benefits were from exercise alone, or due to other health-related factors. Some studies accounted for factors like weight and smoking, while others did not.
The findings tended to support the new federal guidelines, said Dr Sattelmair, from the electronic health record company Dossia who led the research while at the Harvard School of Public Health in Boston.
Taken together, people who exercised according to the minimum guidelines (equivalent to burning about 550 calories per week through exercise) had a 14% lower risk of heart disease than those who didn't exercise at all.
For those who met the higher guideline standard (about 1100 calories per week), that improved to a 20% lower risk, the researchers reported online in Circulation.
People who only got half as much exercise as the minimum guidelines also had some heart protection compared to non-exercisers, Dr Sattelmair said. And those who worked out for longer than guidelines recommend continued to reduce their heart risks – but the added benefit levelled off with high amounts of activity.
The study didn't look at the difference between moderate and more vigorous exercise, but researchers said that people who work out intensely get the same or greater benefit from less time than "moderate" exercisers.
While the findings show that more is generally better. "If you're doing nothing, you don't have to start walking an hour a day to achieve benefit," Dr Sattelmair said.
"If you're totally sedentary... as little as 10 to 15 minutes of brisk walking a day was associated with a reduction in risk of heart disease," Dr Sattelmair said. "Everyone can benefit from movement, physical activity and exercise."
(Reuters Health, Genevra Pittman, September 2011)