Everyone tells you to exercise—the government, your doctor, your workout partner, and most of all yourself. For most people, the benefits of exercise are clear, but for some, working out may have unexpected harmful effects.
Researchers reviewed six previous studies and found that eight to 13 percent of people saw one of their cardiovascular risk factors worsen after exercise. Seven percent saw this effect for two or more risk factors together.
It’s long been thought that exercise decreases the risk of cardiovascular disease—such as heart disease or stroke—by improving blood pressure and the levels of “good” cholesterol, triglycerides, and insulin. The new review, published in PLoS One, showed that this is the case for most people.
For a small group, however, exercise is not all good. The harmful effects remained even after researchers took into account other factors—age, amount of exercise, change in fitness during the study, health status and medications. Because few exercise studies follow participants over the long term, this review does not say that the harmful effects will lead to a heart attack or stroke.
The researchers are uncertain why some people are worse off after exercise. Future research will be needed, such as trying to identify which people will be negatively affected. It could be that tweaking the exercise program could eliminate the harmful effects seen by those people.
The researchers suggest that people who are already exercising continue with their regular program. For those who are just starting out with a workout plan, it’s important to have regular check-ups with your doctor to make sure you are headed in the right direction.