Exercising at Night Offers Biggest Benefits to Heart Health, Finds New Obesity Study

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Doing the majority of moderate-to-vigorous physical activity in the evening was linked to better health outcomes for people with obesity compared with exercising at other times of the day, according to an Australian study published on April 10 in Diabetes Care.

Aerobic physical activity (bouts lasting three minutes or longer) that was performed mostly in the evening (from 6 p.m. to midnight) was associated with the greatest reductions in death and heart disease, says coauthor Angelo Sabag, PhD, a lecturer in exercise physiology at the Sydney School of Health Sciences in Australia.

"But the key message from our study is that physical activity at any time is associated with a reduced risk of cardiovascular disease and mortality in adults with obesity," he says. Overall, these findings highlight the importance of physical activity for heart health and mortality, says Dr. Sabag.

Morning, Afternoon and Evening Exercisers Were Followed for 8 Years

To explore the link between the timing of exercise and heart disease and death from any cause, researchers included nearly 30,000 adults with obesity who were age 40 and older from the UK Biobank data. The average participant age was 62, and about 10 percent of the subjects (2,995) were also diagnosed with type 2 diabetes. People were excluded from the trial if they had preexisting heart disease, cancer, or both.

The amount and timing of physical activity of participants was measured by an accelerometer worn 24 hours a day for a week when the study began. All activity was tracked, including any movement during their workday or while doing household chores, as well as structured exercise like running or walking.

Participants were then placed into one of three categories based on when they did the majority of their moderate to vigorous physical activity: morning, afternoon, or evening.

Examples of moderate activity include brisk walking, dancing, and gardening, and vigorous intensity activities include jogging, running, fast cycling, fast swimming, and walking briskly up a hill.

Researchers linked that information to health data from the National Health Services and National Records of Scotland to follow participants' health trajectory for 7.9 years. During the follow up, there were 1,425 deaths, 3,980 cardiovascular events, and 2,162 microvascular dysfunction events like decreased nerve, kidney, or eye function (neuropathy, nephropathy, or retinopathy).

To try to zero in on the impact of physical activity timing, researchers controlled for numerous factors including demographics, smoking, alcohol consumption, diet, and sleep.

People Who Exercised in the Evening Had a Lower Risk of Death

When participants were compared with a control group who had no bouts of moderate to vigorous physical activity, researchers found:

• People who did the majority of their aerobic physical activity between 6 p.m. and midnight had the lowest risk of premature death and death from heart disease.
• More activity in the evening was associated with a 61 percent lower risk of dying from any cause, afternoon activity associated with a 40 percent lower risk, and morning activity associated with a 33 percent lower risk.
• More activity in the evening was associated with a 36 percent lower risk of dying from heart disease, afternoon activity was associated with a 16 percent lower risk, and morning activity associated with a 17 percent lower risk.
• Evening exercise was also linked with a lower risk of neuropathy, nephropathy, or retinopathy. The risks were decreased 24 percent for evening activity, 16 percent for afternoon, and 21 percent for morning.
• The frequency of the evening physical activity also appeared to be more important than their total amount of daily physical activity.

While more research is needed to show that the timing of activity caused the decreased risks, this study suggests that the timing of physical activity could be an important part of the recommendations for future obesity and type 2 diabetes management, and preventive healthcare in general, says Sabag.

Exercising Later in the Day May Compensate for Decreased Insulin Sensitivity

These findings make sense given previous research that's shown that there is a circadian rhythm to insulin sensitivity, says Matthew Kampert, DO, a physician in sports medicine and endocrinology and director of exercise medicine at the Endocrinology and Metabolism Institute at Cleveland Clinic in Ohio. "Some believe that this decreased insulin sensitivity during evening hours was developed to protect against hypoglycemia (low blood sugar) throughout the night, when people would typically not consume food," says Dr. Kampert, who was not involved in the study.

For people who cannot produce more insulin to compensate (like many of the people living with obesity included in the study), undertaking physical activity later in the day may be offsetting some of the evening-related insulin resistance, says Sabag.

There are two main ways that exercise lowers blood sugar:

• Physical activity increases insulin sensitivity, so your muscles cells are more able to use any available insulin to take up glucose (sugar) during and after activity.
• When your muscles contract, your cells are able to take up glucose and use it for energy even if insulin isn't available.

"While this interpretation provides some insight into potential mechanisms, further research is required to gain a more comprehensive understanding of such processes," says Sabag.

Could Some of the Benefits Be Caused by What People Weren't Doing at Night?

There is evidence that late night eating and snacking tends to include more highly processed foods. Could some of the risk reduction be because of what the evening exercisers weren't eating?

Although the study controlled for many factors, it is much harder to control for dietary factors, says Sabag. Researchers had to rely on self-reported food recall and diaries for the participants' diet. "Nonetheless, we controlled for fruit and vegetable consumption and diet quality index, and the results remained consistent," he says.

Should You Start Exercising in the Evening?

This study established only an association, not causation, points out Kampert. "It is most important to meet recommended guidelines for exercise first, before worrying about what time of day is ideal," he says.

Physical activity guidelines recommend 150 minutes of moderate-intensity exercise per week and two days of muscle strengthening (resistance training or weights) per week.

"Despite all the existing knowledge around the health benefits of exercise, only 1 in 4 adults are meeting current physical activity recommendations," says Kampert.

Sabag agrees, as this study shows that physical activity at any time of day improved outcomes compared with people who weren't active. "Health professionals and guidelines should encourage individuals to incorporate or structure their physical activity into a routine that is sustainable in the long term in order to yield greatest health improvements," he says.

But for people with more flexible schedules and metabolic complications such as obesity, metabolic syndrome, or diabetes, scheduling physical activity in the evening may help better regulate glucose levels and reduce cardiovascular and all-cause mortality risk, he says.

Does Exercising in the Evening Interfere With Sleep?

"Some reports show that exercise, particularly of high intensity, may interfere with sleep duration and quality, however the jury is still out," says Sabag.

For a long time, the conventional wisdom recommended not exercising for at least a few hours before bedtime. However, recent research suggests that evening physical activity doesn't interfere with sleep.

A meta-analysis of 23 studies also concluded that exercise later in the day didn't cause sleep problems, but that people should avoid vigorous exercise at least one hour before bedtime.