- Previous studies show that having poor cardiometabolic health can potentially increase a person’s risk for heart disease and type 2 diabetes.
- Past research has also demonstrated that making healthy lifestyle choices, such as being physically active, may help lower a person’s risk for cardiometabolic disease.
- A new study found that while physical activity may help lower a person’s cardiometabolic risk, the time of day they exercise may also play an important role.
“Cardiometabolic diseases remain the leading cause of morbidity and mortality worldwide,” Prashant Rao, MBBS, MRCP(UK), FACC, sports cardiologist and physician-scientist in the Division of Cardiovascular Medicine in Beth Israel Deaconess Medical Center at Harvard Medical School, told Medical News Today.
“Even small improvements in risk at a population level can translate into substantial reductions in disease burden. Identifying modifiable behaviors, especially ones that are simple and scalable, remains a major public health priority,” he said.
The results of the study are yet to be published in a peer-reviewed journal.
For this study, researchers analyzed health data from almost 14,500 participants of the All of Us study. Data included heart rate data from participants’ Fitbits, and exercise was assessed every 15 minutes throughout the day.
Scientists then looked for links between the times of day participants exercised and cardiometabolic risk factors, such as high blood pressure, obesity, and type 2 diabetes.
“There is growing recognition that biology is not static across the day,” Rao said. “Many important metabolic and cardiovascular processes follow circadian rhythms. Despite this, exercise recommendations have largely ignored timing. We wanted to test whether timing represents an independent and clinically relevant dimension of exercise behavior in real-world populations.”
At the study’s conclusion, Rao and his team found that participants who exercised in the morning, when compared to those who exercised in the evening, were:
- 35% less likely to have obesity
- 31% lower chance of developing coronary artery disease
- 30% lower risk for type 2 diabetes
- 21% less likely to have hyperlipidemia
- 18% lower chance of developing high blood pressure
This shows that when people exercise may be just as important as how much they exercise. The study also found that exercise performed between 7:00 a.m. and 8:00 a.m. was specifically associated with the lowest odds of coronary artery disease.
“Importantly, these associations were independent of total physical activity, indicating that timing is not simply a proxy for ‘more exercise,’ but may reflect an additional behavioral or biological signal,” Rao said.
“Exercise timing may represent a previously underappreciated dimension of exercise and cardiometabolic health. While any exercise is beneficial, morning exercise may confer additional advantages.”
— Prashant Rao, MBBS, MRCP(UK), FACC
“The next step is to move from association to causation,” Rao added. “I think these findings should motivate a large randomized trial of exercise timing. Ultimately, the goal is to determine whether we can optimize exercise prescriptions not just by dose, but by timing.”
MNT spoke with Cheng-Han Chen, MD, a board certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, about this study.
“This study found that exercising in the morning was associated with lower levels of cardiometabolic risk factors such as coronary artery disease, high blood pressure, high cholesterol, diabetes, and obesity,” Chen commented. “This is an interesting finding that should stimulate more research into specific timing of exercise for the greatest health benefit.”
“Cardiovascular disease continues to be the
MNT also spoke with Brett A. Sealove, MD, FACC, FAHA, RPVI, CPE, chair of cardiology at Hackensack Meridian Jersey Shore University Medical Center, and associate professor and vice chair of cardiology at the Hackensack Meridian School of Medicine in New Jersey, who said he sees the consequences of cardiometabolic disease every day: heart attacks, heart failure, strokes, and amputations.
“We’ve known for decades that exercise is one of the most powerful medicines,” Sealove explained. “It should not be overstated that exercise is one of our biggest problems in the U.S., as it is one of the best solutions for cardiac health and longevity, anytime, anywhere.”
“However, this study takes that knowledge a step further by helping those who want to optimize their risk reduction, especially if the timing of exercise matters,” he added.
MNT also asked Sealove why exercising in the morning could help lower cardiometabolic risk more effectively than exercising in the evening.
“First, consider the role of circadian rhythms,” Sealove said. “Our bodies are controlled by internal biological clocks that regulate nearly every metabolic process, including cortisol secretion, insulin sensitivity, glucose uptake, and fat oxidation.”
“In the early morning, cortisol levels naturally increase, preparing the body for activity. Insulin sensitivity, especially in skeletal muscle, also tends to be higher in the morning. Aligning exercise with these circadian signals may improve metabolic responses in ways that evening workouts cannot,” he explained.
“Second, morning exercise, often performed in a fasted or semi-fasted state, may promote greater fat oxidation,” he continued. “When the body’s carbohydrate stores are lower after an overnight fast, it more readily breaks down fat for fuel during exercise. This increase in fat utilization could, over time, lead to better lipid profiles and reduced visceral fat, lowering cardiometabolic risk.”
“Third, there is a practical behavioral aspect. Morning exercisers tend to be more consistent because there are fewer competing demands early in the day. Consistency is crucial in exercise medicine. Along with adherence over months and years, it contributes to the long-term reduction in disease risk observed in this study.”
— Brett A. Sealove, MD, FACC, FAHA, RPVI, CPE
