Women's Health Discovery

The timing of exercise

Although many studies have shown that physical activity improves heart health in patients with type 2 diabetes, few have considered whether exercising at a certain time of day provides an extra health benefit for this population. Now, a study by HMS investigators at Joslin Diabetes Center and Brigham and Women’s Hospital, along with collaborators, gives insight, reporting a correlation between the timing of moderate-to-vigorous physical activity and cardiorespiratory fitness and health risks in individuals who have type 2 diabetes and who are obese or overweight.

When the researchers analyzed data on more than 2,000 people, they found that men who have type 2 diabetes or are obese or  overweight and exercise in the morning had higher cardiorespiratory fitness compared with men with these conditions who are most active midday. The findings were independent of the amount and intensity of weekly physical activity. Notably, men with these conditions who exercise in the morning also had a higher chance of developing coronary heart disease in the next four years than individuals in all other exercise groups.

For women, no link between the timing of physical activity and coronary heart disease risk or cardiorespiratory fitness was found.

Sex-specific physiological differences may help explain the more prominent correlations seen in men, who tend to be at risk of coronary heart disease earlier in life. However, the researchers note that other factors could be at play, such as the effect the circadian system has on time-specific physical activity.

The researchers, for example, could not account for participants’ varying circadian rhythms: a jog at 6 p.m. for one participant may be “evening exercise” while for another participant who wakes later in the day, it may biologically be “afternoon exercise.” There is a growing interest in the interaction between physical activity and the circadian system, according to the researchers.

Qian J et al., Diabetes Care, February 2021

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