Regular exercise may increase the risk of heart disease and diabetes in some people, potentially uncovering a group of individuals genetically predisposed to suffer from working out, researchers said.

While most benefit from physical activity, 8 percent to 13 percent of individuals had a worse level of blood pressure, cholesterol, triglycerides, or insulin after exercise, according to the study published by the journal PloS. All of the body indicators measured are risk factors for heart disease and diabetes.

“The causes of the phenomenon are unknown,” the study authors wrote.

The U.S. Department of Health and Human Services recommends adults log 150 minutes of moderate-intensity exercise a week for “substantial health benefits,” according to its 2008 guidelines.

“Being physically active is one of the most important steps that Americans of all ages can take to improve their health,” the department said on its website.

The analysis released Wednesday looked at six earlier studies involving more than 1,600 mostly obese adults, testing how a variety of people reacted to exercise programs. About 7 percent had adverse changes in two or more of the risk factors examined.

Prior health status, age, sex, or race didn’t appear to influence who ended up in this group, the authors said. One of the reports included in the research found a genetic component was related to how some individuals responded to physical activity, a potential clue for discovering what makes these people different.

“It may be possible with further research to identify molecular predictors of the inability to benefit from regular exercise,” the researchers said.

Copyright 2012 Bloomberg News