Exercise may actually worsen the health of some individuals, according to a recent Duke study.
The study, titled “Adverse Metabolic Response to Regular Exercise: Is It a Rare or Common Occurrence?,” shows that between 8 to 10 percent of individuals have adverse responses, or a worsening in an aspect of their health, to exercise, contradicting advice given by physicians and other health professionals. The authors evaluated data from six exercise studies involving 1,687 people. They measured four markers of cardio-metabolic health: blood pressure, triglycerides, fasting insulin—a marker of glucose control and tendency toward diabetes—and HDL cholesterol—an essential fat sometimes referred to as “good” cholesterol.
“[The authors of the study] are pretty careful [with their research] and they’re all exercise fanatics, so it’s probably hard for them even to think that there are people who are harmed by exercise,” said Dr. Robert Califf, vice chancellor for clinical and translational research and director of the Duke Translational Medicine Institute.
Exercise levels ranged from moderate levels, such as brisk walking, to vigorous jogging, Dr. William Kraus, co-author of the study and professor of medicine at Duke, wrote in an email Sunday. Ten percent of people got worse on one of the four markers, all of which are related to heart disease, in the study. Although many individuals responded poorly in one of the parameters, they did not necessarily react the same in another. Only 7 percent of subjects got worse in multiple categories.
“There was no relation between [the markers],” Kraus noted. “This means that exercise was likely to help one of the risk factors for everyone, and likely to be less helpful or lead to an adverse outcome in another.”
Califf noted that even if someone had an adverse response in one of the parameters, they could take medicine to correct it and continue exercising. For example, if somebody exercises to bring his or her cholesterol level down but it increases blood pressure, then he or she would take blood pressure medicine and maintain their exercise.
Although several patients displayed negative responses to exercise, an equal number of those studied were “super responders,” meaning they had a more favorable response than expected, Kraus said, adding that the statistical distribution was not due to seasonal variances or changes in medication use.
“Most [patients] had some cardio-metabolic risk factors such as cholesterol or lipid abnormalities, mildly elevated blood pressure, [among others],” Kraus said. “Few, if any, were on medications.”
The next step, Kraus said, is to understand how to predict if one will be an adverse or super responder for any given category or health benefit. He added that doing so will allow physicians to individualize exercise “prescriptions” for patients.
Califf agreed that the results need more studying, noting that there is likely a biological rationale for the negative effects of exercise in some people.
“The only effect this study should have is to emphasize the need to measure these key parameters and then respond to them,” Califf said. “I don’t think it will change the fundamental advice which is to eat less and exercise.”
Physical activity is still important in keeping most people healthy, Neva Avery, exercise physiologist and internship coordinator at the Duke Diet and Fitness Center, wrote in an email Tuesday.
“It’s important to understand that the benefits of regular physical activity are still abundant for the greatest majority of the population and those benefits far outweigh any risks,” she said. “There is far greater health risk of being sedentary [versus] being active for most individuals.”