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 study.
And among people already accustomed to getting the blood flowing, those who go above and beyond on physical activity seem to have the best heart outcomes, said researchers who analyzed past data on exercise and heart disease risks.
"Exercise is good, more exercise is better," said David Swain, an exercise scientist at Old Dominion University in Norfolk, Virginia, who was not involved in the new research.
"There's a continuous improvement in your health and your reducing of heart disease the more physical activity you do," he told Reuters Health.
Still, Swain cautioned, people who are at risk of heart disease and not used to working out should take it slow, and consult their doctor, when they're starting out.
Researchers have known that exercise is good for heart health for decades. Pounding the pavement on a regular basis helps reduce blood pressure and improves blood flow in the heart, Swain said.
The authors of the new study, led by Jacob Sattelmair, wanted to test the benefit of exercise on heart disease in relation to new federal guidelines to provide a better picture of just how much activity is necessary for heart protection.
United States guidelines from 2008 recommend 150 minutes of moderate exercise (such as brisk walking) 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 to see who was diagnosed with heart disease over anywhere from a few years to a couple 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 of the studies took into account factors like weight and whether participants smoked, while others did not.
The findings tended to support the new federal guidelines, said 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 percent 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 percent lower risk, the researchers reported in Circulation.
People who only got half as much exercise as the minimum guidelines also had some heart protection compared to non-exercisers, Sattelmair said. And those who worked out for longer than guidelines recommend continued to reduce their heart risks -- but the added benefit leveled off with high amounts of activity.
About one in eight adult Americans suffers from heart disease, the leading killer worldwide.
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," Sattelmair said.
Jumping off the couch into a running routine might also be worrisome for people who are at risk for heart disease, Swain added, and they should ease into exercise and discuss it with their doctor. Being overweight and having diabetes or high cholesterol adds to heart risks.
"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," Sattelmair told Reuters Health. "Everyone can benefit from movement and physical activity and exercise."