(Reuters Health) - Adults with a healthy weight but a sedentary lifestyle may have the same risk for heart attacks or strokes as people who are overweight, a recent study suggests.

Researchers found that normal-weight people who spent much of the day sitting but still hit minimum recommended weekly exercise targets of 150 minutes of moderate activity had about a 58 percent lower risk of a heart attack or stroke than overweight people.

But when individuals with a normal weight sat around most of the time and got very little exercise, their risk of serious cardiac events wasn’t significantly different from that of overweight people.

“Being at normal weight is not sufficient to be healthy,” said lead study author Arch Mainous of the University of Florida in Gainesville.

“This matters for patients because they may get a false sense of security by just looking at the number on the scale,” Mainous said by email. “A sedentary lifestyle can erode the advantage of a healthy weight and increase the cardiovascular risk to that of their overweight counterparts.”

When people are sedentary - especially in middle age and beyond - they lose lean muscle mass and cardiorespiratory fitness, Mainous said.

Participants in the current study were ages 40 to 79, without a history of heart disease. Researchers used the standard American College of Cardiology/American Heart Association risk-factor calculator (www.cvriskcalculator.com/) to assess people's risk of events like heart attacks and strokes. A high risk was at least a 7.5 percent chance of this happening over the next decade. A "low risk" was a less than 7.5 percent chance.

Researchers identified people as being at a healthy weight if they had a body mass index (BMI, a ratio of height to weight) of 18.5 to 24.9 and overweight if their BMI was from 25 to 29.9. (A BMI calculator is online here: bit.ly/2tXeEf4.)

Overall, 35 percent study participants had a high risk of events like heart attacks or strokes when risk factors other than BMI were also taken into consideration, researchers report in the American Journal of Cardiology.

Among individuals with a normal-range BMI, about 30 percent had a high risk of cardiac events.

For example, when researchers looked at fat in the gut region (or “sagittal abdominal diameter”), they found normal-weight participants with too much of this fat were more than twice as likely to be at a high risk of cardiac events as participants with a normal BMI and without much of this fat.

And, adults with a normal BMI who got short of breath during exercise were 35 percent more likely to have a high risk of heart attacks and strokes than normal-weight individuals who didn’t have breathing issues with exertion.

One limitation of the study is that researchers measured respiratory fitness based on how often participants reported shortness of breath, and not with objective breathing or exercise tests.

Even so, the results underscore the importance of staying active even with a healthy BMI, said Dr. Michael Hall, a researcher at the University of Mississippi Medical Center in Jackson who wasn’t involved in the study.

“While being in the normal-weight BMI category is good, reducing sedentariness and increasing physical activity still has important benefits,” Hall said by email.

“Unfortunately, many people have sedentary jobs, so it is important to work in time for moderate to vigorous exercise,” Hall added. “Small things like taking the stairs, adding in a few brief walks in the day or other intermittent activities may help attenuate some of the risks associated with sedentary behavior.”

SOURCE: bit.ly/2RN7CZP American Journal of Cardiology, online December 4, 2018.