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When you exercise may have more to say about your health.

George Eliot wrote in Middlemarch (1): “It’s an uncommonly dangerous thing to be left without any padding against the shafts of disease.” In those days diseases such as tuberculosis caused weight loss, so there was a viewpoint that one needed to be voluptuous to be healthy. These days we know that maintaining an ideal body mass index (BMI) is important for health, and for many people this means increasing their amount of daily exercise. 

Every conversation about exercise offers conflicting advice. Is exercising in the morning better than in the evenings? Should one eat breakfast before exercise? Is it OK to go to the gym soon after waking up? From doctors to gym trainers to social media influencers—everyone claims to have answers, the problem being they all seem to say different things. A six-pack looks good, but is it healthy? Maybe an ample bottom means a springy heart. There seems to be no consensus, only conflict, and utter confusion. And exercise trends come and go—everyone raves about a new gym or F-something workout. Exercise does throw some endorphin-laced punches, but barrages can be damaging. 

Hippocrates, widely regarded as the “father of medicine”, wrote: “Even when all is known, the care of a man is not yet complete, because eating alone will not keep a man well; he must also take exercise. For food and exercise, while possessing opposite qualities, yet work together to produce health.” (2) Exercise is good. That much we know is true, but when—more specifically, at what time of the day?

Recently, a study looked to answer this question about the best time to work out. Researchers from Franklin Pierce University, New Hampshire in America along with a team in Hong Kong studied more than five thousand people undertaking moderate to vigorous physical activity. They were divided into three groups based on the timing of their exercise: morning, afternoon, and evening. The findings were quite interesting: People that exercised in the mornings ended up with a lower body-mass-index (BMI) i.e., lost more weight than those that exercised in the afternoons or evenings. Even when morning exercisers were more sedentary for the rest of the day, the timing of exercise in the morning appeared to matter the most. In this study, the desired benchmark was set at 150 minutes of moderate to vigorous physical exercise a week, but in the morning group it mattered less if one did not achieve this. Further, the optimal exercise timing was found to be 7 to 9 AM in the mornings to gain the most benefit, if one was looking to lose weight. These findings were backed up by another report, a Women’s Health Study where accelerometers were used. Accelerometers are devices that literally measure acceleration and vibration of a moving body. When used in a fitness tracking device, an accelerometer is more accurate because it also measures tilt and position, and records most steps taken by an individual accurately. This study on over seven thousand older women with an average age of 70 showed that women who over time had accumulated less morning exercise gained more adiposity. Less morning exercise essentially means more fat: women who recorded <39% accelerometer counts before 12 noon had a 26% higher risk of being obese.

Until now I have been discussing exercise and weight loss, but what about specific health outcomes? We know that accumulating more body fat increases the risk of Type 2 diabetes and this is because fat causes insulin resistance in tissues alongside other metabolic problems. When it comes to people with metabolic diseases such as diabetes, does the timing of exercise matter? A team from Harvard University decided to look at this very question. Chirag J. Patel, associate professor of biomedical informatics at Harvard Medical School, Massachusetts, and his team examined more than 90,000 people and found that morning and afternoon, but not evening, exercise reduced the risk for type 2 diabetes.

In this study looking at Type 2 diabetes and the timing of exercise, people were divided into morning, afternoon and evening exercisers and their consistency of sticking to these patterns was also studied. People wore accelerometers and the exercise was measured in units of METs (metabolic equivalent of tasks). This is sometimes used to study the metabolic rate of our body as I explained in my book, Skin a Biography (4th Estate): “To standardize metabolism studies, a unit has been created to measure metabolic rates: met (short for ‘metabolic equivalent). 1 met = 58.15 W/m2 (watts per square metre). A person has a BMR of 0.7 met when sleeping; 2 met when walking slowly, 4 to 8 met when swimming, and 8 to 12 met when playing tennis.” 

The Harvard study showed that using MET as the physical activity measure, there were protective associations of morning and afternoon exercise but no evidence for evening physical activity being protective against, or beneficial for type 2 diabetes. Interestingly, in this case –unlike in the earlier studies I mentioned looking purely at physical activity and weight loss—there was no difference between morning and afternoon physical activity.

I found these studies interesting. Although I am an early riser, I leave for work early and work long hours, so usually only find time to exercise at night. Except on weekends, when I manage a long run in the mornings. These studies were news to me. I write these blogs to educate my patients and for those interested in following my work and research, and while looking for topics for this blog I learn a lot myself. Maybe as Konrad Lorenz wrote (3): “It is a good morning exercise for a research scientist to discard a pet hypothesis every day before breakfast. It keeps him young.”

THE END

(1) George Eliot, Middlemarch (New York: Penguin Classics, 2003), page 76.
(2) Regimen, Hippocrates, translation by W. H. S. Jones (1931), Vol. 4, page 229.
(3) Aggression, Konrad Lorenz (translation by M. Latzke (1966), page 8.