Regular exercise has long been hailed as a great way to preserve heart health, but could a morning workout deliver more benefits than an evening visit to the gym?
New research suggests that for women in their 40s and up, the answer appears to be yes.
"First of all, I would like to stress that being physically active or doing some sort of exercise is beneficial at any time of day," noted study author Gali Albalak, a doctoral candidate in the department of internal medicine at Leiden University Medical Centre in the Netherlands.
Indeed, most public health guidelines ignore the role of timing altogether, Albalak said, choosing to focus mostly on "exactly how often, for how long and at what intensity we should be active" to gain the most heart health benefits.
But Albalak's research focused on the ins and outs of the 24-hour wake-sleep cycle — what scientists refer to as circadian rhythm. She wanted to know whether there might be "a possible additional health benefit to physical activity" based on when people choose to exercise.
To find out, she and her colleagues turned to data previously collected by the UK Biobank that tracked physical activity patterns and heart health status among nearly 87,000 men and women.
Participants ranged in age from 42 to 78, and nearly 60% were women.
All were healthy when outfitted with an activity tracker that monitored exercise patterns over the course a week.
In turn, heart status was monitored for an average of six years. During that time, roughly 2,900 participants developed heart disease, while about 800 had a stroke.
By stacking heart "incidents" up against exercise timing, the investigators determined that women who primarily exercised in the "late morning" — meaning between approximately 8 a.m. and 11 a.m. — appeared to face the lowest risk for having either a heart attack or stroke.
When compared with women who were most active later in the day, those who were most active in either the early or late morning were found to have a 22% to 24% lower risk for heart disease. And those who mostly exercised in the late morning saw their relative risk for stroke drop by 35%.
Yet, the increased benefit of morning exercise was not seen among men.
Why? "We did not find any clear theory that could explain this finding," Albalak noted, adding that more research will be needed.
She also stressed that her team's conclusions were based on an observational analysis of exercise routines, rather than on controlled testing of exercise timing. That means that while exercise timing decisions appear to affect heart health, it's premature to conclude that it causes heart risk to rise or fall.
Albalak also stressed that she and her team are very much "aware that there are societal issues that prevent a large group of people from being physically active in the morning."
Still, the findings suggest that "if you have the opportunity to be active in the morning — for example on your day off, or by changing your daily commute — it wouldn't hurt to try and start your day with some activity."
The findings struck one expert as interesting, surprising and somewhat mystifying.
"An easy explanation does not come to mind," admitted Lona Sandon, program director of the department of clinical nutrition at UT Southwestern Medical Center's School of Health Professions, in Dallas.
But to gain better insight into what is happening, Sandon suggested that going forward it could be helpful to gather information on participants' eating patterns.
"From nutrition research, we know that satiety is greater with morning food intake than it is with evening intake," she said. That could point to a difference in the way metabolism operates in the morning versus the evening.
That could mean that "the timing of food intake prior to the physical activity could impact the nutrient metabolism and storage that might further impact cardiovascular risk," Sandon added.
It could also be that morning workouts tend to lower stress hormones more than late-day exercising. If so, over time that could also have an impact on heart health.
In any case, Sandon echoed Albalak's acknowledgment that "any exercise is better than no exercise."
So "exercise at the time of day you know you will be able to stick to a regular schedule," she said. "And if you can, take a morning physical activity break instead of a coffee break."
The report was published Nov. 14 in the European Journal of Preventive Cardiology.