Timing may matter as much as the workout itself. A new study found that people who exercise in the morning are significantly less likely to develop type 2 diabetes, coronary artery disease, and other cardiometabolic conditions compared to those who are active later in the day.
The research, presented at the American College of Cardiology's Annual Scientific Session this week, analyzed data from 14,489 participants enrolled in the All of Us national study. Researchers used Fitbit-derived heart rate data collected over one year, tracking minute-by-minute fluctuations to identify periods of elevated heart rate lasting 15 consecutive minutes or more. That method differs from most exercise studies, which typically log specific activities like walking or gym sessions. Here, the measure was the body's own physiological response.
Participants were then grouped by when they most frequently hit those activity windows. After accounting for age, sex, total activity level, sleep duration, smoking status, and alcohol use, morning exercisers came out ahead on nearly every measure. Compared to people who exercised later in the day, frequent morning exercisers were 31% less likely to have coronary artery disease and 18% less likely to develop certain other cardiovascular conditions. The risk reduction for type 2 diabetes reached 30%.
"Any exercise is going to be better than no exercise, but we tried to identify an additional dimension relating to the timing of exercise," said Prem Patel, a medical student at the University of Massachusetts Chan Medical School and the study's lead author. "If you can exercise in the morning, it seems to be linked with better rates of cardiometabolic disease."
Researchers acknowledged that it remains unclear whether the timing of exercise directly causes the health differences or whether other factors are at play. The study has not yet been published in a peer-reviewed journal. Still, Patel and his colleagues suggested the findings could shape how clinicians counsel patients about physical activity, adding a more specific layer to general exercise recommendations.
