BOSTON — More than 34.2 million Americans suffer from diabetes, 90-95% of whom have the Type 2 form caused by poor diet and lack of exercise. Numerous studies have demonstrated the role of physical activity in improving heart health for patients with Type 2 diabetes. Now, scientists report that the time of day a patient exercises is highly important when it comes to heart health.
According to their research, men with diabetes who exercise in the morning face a greater risk of suffering a heart attack.
“The general message for our patient population remains that you should exercise whenever you can, as regular exercise provides significant benefits for health. However, researchers studying the effects of physical activity should take into account timing as an additional consideration so that we can give better recommendations to the general public about how time of day may affect the relationship between exercise and cardiovascular health,” says study corresponding author Dr. Jingyi Qian, of Brigham and Women’s Hospital and an instructor of medicine at Harvard Medical School, in a statement.
Because Type 2 diabetes is linked to unhealthy lifestyles, Qian’s team analyzed more than 2,000 patients who were also obese or overweight. They identified a link between the timing of exercise and the risk of developing heart disease.
Study authors used data from the Look AHEAD (Action for Health in Diabetes) study that began in 2001. It monitored the health of overweight or obese patients in the U.S. with Type 2 diabetes. For a week, participants wore accelerometer devices on their waists that measured the time and type of their physical activity.
“The study population was very well characterized at baseline, with detailed metabolic and physical activity measurements, which was an advantage of using this dataset for our work,” says co-corresponding author Dr. Roeland Middelbeek, of the Joslin Diabetes Center in Boston.
Researchers tracked the “clock-time” of daily moderate-to-vigorous activity. This included labor-intensive work that extends beyond more traditionally defined forms of exercise.
To assess the volunteers’ chances of experiencing coronary heart disease over the next four years, the researchers used a measure called Framingham Risk Score. It uses an algorithm based on information about a person’s age, sex, blood pressure, cholesterol and smoking history.
The study finds that men who performed physical activity in the morning have the highest risks of developing coronary heart disease, irrespective of the amount and intensity of weekly exercise. Men who were most active around midday had lower cardio-respiratory fitness levels. In women, the investigators did not find an association between specific activity timing and coronary heart disease risk or cardiorespiratory fitness.
Sex-specific physiological differences may help explain the more prominent correlations seen in males, who tend to be at risk earlier in life. However, researchers say other factors could also be at play. It remains unclear why time-specific activity may be associated with different levels of health and fitness.
The researchers also could not account for participants’ varying circadian rhythms. It was unknown whether a person was a “night owl” or “morning lark.” Whereas a jog at 6 p.m. for one participant may be “evening exercise,” another participant prone to waking later in the day may, biologically, consider it to be “afternoon.” This is regardless of how the clock-time of the activity was recorded in the study.
“Interest in the interaction between physical activity and the circadian system is still just emerging. We formed a methodology for quantifying and characterizing participants based on the clock-time of their physical activity, which allows researchers to carry out other studies on other cohorts,” says Dr. Qian.
Beyond further integration of circadian biology with exercise physiology, the researchers are also excited to use longitudinal data to investigate how exercise timing relates to heart health outcomes, particularly among diabetes patients more vulnerable to cardiovascular events.
Findings are published in the journal Diabetes Care.
SWNS writer Mark Waghorn contributed to this report.