Circadian Clock Plays a Role in Health, Peak Performance

Fran Lowry

May 08, 2019

Circadian clock genes are expressed in all tissues in the body, with the highest levels found in skeletal muscles, according to recent research.

"That was a surprise. We used to think the clock was only in the brain, but now we know that the clock genes are expressed throughout all tissues in the body," said Joseph Takahashi, PhD, from the University of Texas Southwestern Medical Center and the Howard Hughes Medical Institute in Dallas.

Takahashi and his team of researchers first identified the clock gene in 1994. The circadian clock "is a gene network that turns on and off once each day," he explained. "Those genes are actually master-control genes that turn on and off many hundreds of thousands of other genes that are involved in every process in cells and in the body."

The implications for sports medicine are obvious.

"Peak performance occurs when the body is in sync with its circadian clock," said Karyn Esser, PhD, from the University of Florida in Gainesville.

"If you want to perform your best in any athletic endeavor," it is essential to know the optimal times to eat, sleep, rest, and exercise, all of which are regulated by your clock, she told Medscape Medical News.

Research on the role of circadian rhythms and the molecular clock mechanism in skeletal muscle homeostasis and health was pioneered in Esser's lab. She will chair a session on the biologic and physiologic mechanisms of exercise, circadian rhythm, and sleep at the upcoming American College of Sports Medicine 2019 Annual Meeting in Orlando.

The discovery that "there is a genetic mechanism that's inside every single cell in your body that is a time keeper" has opened the field of circadian biology to humans, and now it is emerging as a factor in human health and medicine, Esser explained.

When the clocks in your body out of alignment, it can feel like jet lag, she said. "Your brain is in one time zone, your heart is in another, your intestines in another, muscles in another, and so on. And you only start to feel better when things get back in synchrony."

Our clocks can be affected by everyday activities "in very basic and profound ways," she said. For example, using an e-reader can expose us to light when we would not typically be exposed to it, and eating late at night can affect our circadian biology.

And a disrupted circadian cycle can lead to, among other things, hyperglycemia, an increase in mean arterial blood pressure, insulin resistance, and type 2 diabetes.

The concept of circadian medicine is being integrated into active practice by clinicians at various centers, and has implications for the way we set up our clinics, hospitals, and intensive care units, Esser said.

"If a physician has to do an all-nighter in the ICU for a day or two, that's not a big deal. But if you do it chronically, it can become a big deal," she pointed out.

The New Holy Trinity: Nutrition, Exercise, and Sleep

"We have a master clock in our brain that tells us when we should be sleeping and when we should be awake, physically active, and eating," said Kenneth Wright Jr, PhD, from the University of Colorado Boulder.

"When these things are in sync with each other, our physiology is optimal," he told Medscape Medical News.

For example, a lot of Olympic and world records are broken in the afternoon and early evening hours, because that's when our circadian system is really optimizing our performance, said Wright, who will discuss effects of the circadian clock and sleep on health and athletic performance at the meeting.

Peak performance times are different for early birds and night owls, characteristics that are determined by the circadian clock, he noted.

But either way, adequate sleep is essential. "If your sleep is disturbed, then your performance, including reaction time and decision-making ability, is impaired," he added.

For people competing at the peak of their athletic ability, small things like sleep can make a huge difference, he said.

A lack of sleep can "impair our ability to regulate our blood sugar. It will alter certain hormones in terms of their release. Many professional football players have sleep apnea, which fragments their sleep, is not as restorative," and limits the release of growth hormones that normally occurs during deep sleep, Wright explained.

A healthy lifestyle consists of nutrition, physical activity, and sleep, like a "three-legged stool," he said. "If you short change one of those three things, it is going to impair your health."

Disturbances in sleep and circadian rhythms can lead to "endocrine disorders, immune disorders, cardiovascular disease, and neurologic disorders," and increase "our risk of obesity, diabetes, depression, and cognitive impairment," he reported.

In today's society, there will always be some sleep loss and disruption of the clock. However, "we are now recognizing that we need to minimize this as much as possible because of the ill effects on long-term health," he said.

Nowadays, everyone acknowledges that cigarette smoking leads to disease and is a public health problem. "I really think we are at a stage now with sleep," Wright said.

"Poor sleep is not just about our ability to not be tired the next day, it's about long-term health," he added.

Takahashi, Esser, and Wright have disclosed no relevant financial relationships.

American College of Sports Medicine (ACSM) 2019 Annual Meeting. To be presented May 29, 2019.

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