For many of us who have trouble getting through a working week with demands of family and household chores, we wonder at the stamina of celebrities who traverse the globe through time zones, train and perform for days and weeks on end, and still manage peak performance with an inner glow.
While teams of experts and expensive skincare routines help, many of the top performers are actually listening to their body clocks.
Olympic athlete Usain Bolt and former tennis star Venus Williams insisted on up to 10 hours’ sleep per day, while Roger Federer is reputed to sleep 12 hours a day; and most athletes insist on at least eight. To maximise performance, many athletes have said they stick to a rigid diet, often with no food after 7pm and a consistent daily routine built around nutrition and sleep.
A study at Stanford University in California, published in Scientific Reports (2020) backs up the importance of the biological clock in peak performance. Postdoctoral fellow in psychiatry and circadian biologist, Renske Lok, and her colleagues found that Olympic swimmers are more than a third of a second faster if they compete in the evening rather than in the morning. “In 40 per cent of swimming races, the time-of-day effect is bigger than the difference between finishing first or second,” the researchers said.
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Some of us are early birds – tending to go to bed and wake up early, with more energy in the first half of the day – while others are more likely to be full of beans in the evening and night hours. Whether you are an early bird or a night owl depends to some extent on your genetics, but more evidence is emerging of how this variation is influenced by our individual circadian rhythms.
That explains why at parties or weddings, while some are ready for bed at 10pm, other revellers are getting ready to party late into the night.
Your circadian rhythm is your body’s internal clock. Light, sleep patterns, hormones, meals and temperature can all influence your circadian rhythm, which in turn can influence your overall health.
The US Institute of General Medical Sciences explains how the system that controls our inbuilt sense of time works. The body clock is controlled by proteins that are maintained by thousands of genes that switch on and off in a specific order. The peripheral biological clocks in cells and tissues are synchronised by a master clock in the brain in a structure called the suprachiasmatic nucleus (SCN). The SCN controls the production of the hormone melatonin based on the amount of light the eyes receive. In the evening, a person’s master clock tells the brain to make more melatonin, causing sleepiness.
In the past few decades, researchers have been identifying the degree to which our mood, metabolism, athletic performance and cognitive abilities vary over a 24-hour period, while disruption of the body clock is being implicated in a range of health conditions, including type 2 diabetes and cancer.
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Understanding our circadian rhythm means understanding the natural oscillations in our tissues or the literally trillions of clocks, ticking in every cell of our bodies.
A review paper in Clocks & Sleep (2023) summarised the interplay between mealtimes, circadian rhythms, hormones and metabolism. The researchers outlined the importance of synchronisation between the body’s central and peripheral clocks and optimal metabolic function. The research highlighted the importance of aligning mealtimes with the body’s natural rhythms to promote metabolic health and prevent disease. Studies show that consuming meals later in the day is associated with higher prevalence of metabolic disorders, while early time-restricted eating such as having an early breakfast and an earlier dinner improves levels of glucose in the blood.
“Circadian hormones, including melatonin and cortisol, interact with mealtimes and play vital roles in regulating metabolic processes,” the researchers concluded.
Understanding the mechanisms of central and peripheral clock synchronisation, including genetics, sleep duration and hormonal changes provides valuable insights for optimising what to eat and how we eat. This knowledge is a key contributor to overall health and wellbeing.
All those late-night snacks that are out of sync with our peripheral and central circadian clocks are potentially impacting our metabolism in more ways than we realised.
A paper in Physiology (2020) describes how the optimum time for exercise for strength and endurance appears to be between 4pm and 8pm. While the factors contributing to this circadian physiology are not well defined, it appears to involve factors such as body temperature, blood flow and blood pressure that gradually increase during the day, contributing to improved muscle performance in the early evening.
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In Circadian Rhythms (2023), professor of circadian neuroscience Russell Foster and biologist Leon Kreitzman – both at Oxford University – explain how other physiological parameters also vary over the 24-hour period. Testosterone secretion peaks at about 9am; co-ordination tends to be best at about 2.30pm; reactions times are fastest at about 3.30pm; cardiovascular efficiency, muscle and grip strength peak at 5pm to 5.30pm.
Circadian rhythms exist not just in our body but in almost all cells, regulating key processes such as diet, metabolism and peak exercise performance. Depending on what time you sleep, eat and exercise – muscle, fat and other cells will be in a different state and will respond to those activities differently.
The emerging evidence suggests that the old adage: “Eat breakfast like a king, lunch like a prince, and dine like a pauper”, may actually be rooted in science.
- Dr Catherine Conlon is a public health doctor in Cork
