They tell you when it's time to sleep and when it's time to wake up. They are a guide for when to eat, when to exercise, which foods to choose to get the maximum benefit. The most ancient of clocks, they were with us long before we discovered cogs and wheels or even hourglasses and sun dials. As we start to count down the hours until the start of 2019, the Athens-Macedonian News Agency (ANA) got the lowdown on circadian rhythms and how they have run our lives since the dawn of time from Constantinos Dallas, head researcher on environmental physiology at FAME Lab, at the University of Thessaly.
Composed of the Latin words 'circa' (around) and 'diem' (day), the word circadian is used to describe any biological process that presents an endogenous periodic change over a 24-hour period. Each person has their own circadian rhythm and, in all of us, sleep plays a crucial role in maintaining its proper functioning.
The pace of modern life, where work and intense social activity continues until late at night, can affect this cycle of waking and sleeping and this lack of sleep can disrupt a series of bodily functions that the circadian rhythm controls, including dietary habits, body temperature, metabolic rate, cell cycles and differentiation, the cardiovascular and digestive systems, the endocrine and immune systems, as well as our general mental and physical health.
As Dallas noted to the ANA, many chronic ailments have in recent years been linked to disruptions of the circadian rhythm, including serious complaints like diabetes, obesity, depression, bipolar disorder, seasonal emotional disorder and sleep disorders. A series of studies have shown the deep impact that circadian rhythms have on our lives, Dallas said.
One study conducted at Texas University Southwestern Medical Center has linked night shifts and transatlantic voyages to obesity and related ailments, such as diabetes. Another study conducted in London found that sleep deprivation makes people eat more to feel sated, with those sleeping less than 5.5 hours consuming 385 more calories on average per day to those sleeping more than seven hours.
According to researchers at the University of Utah, eating iron affects our liver's biological clock so eating meat late at night can "de-synch" the clocks of the liver and brain, creating metabolic problems.
Another study published in "The Lancet Psychiatry", involving 91,100 people aged 37 to 73 years old, showed that a person with a disrupted circadian rhythm has a 6 pct greater chance of being diagnosed with depression, a 10 pct higher chance of a mood disorder diagnosis and an 11 pct higher chance of a bipolar disorder diagnosis, as well as 9 pct higher chance of experiencing loneliness.
Despite the findings, Dallas pointed out, it is still unclear whether these disruptions are a symptom or a cause of the mental disorders correlated with them but other studies have also shown a clear link between circadian rhythms and performance in sports.
Research conducted to date has show that testosterone levels are highest at around 8:30 in the morning, that the best coordination and reaction times are at 14:30 and the best cardiovascular and muscular performance is achieved around 17:00. Based on this, Dallas noted, the best time for training is determined by what we wish to improve. He advised against exercise around 21:00 at night, since this is when melatonin starts to be secreted and the body prepares itself for sleep, and exercise disrupts this process.
The body's personal clock also plays an important role, however, and the above advice might suit a "morning person" that wakes early but need to be modified for "night owls" that wake up closer to noon. According to Dallas, the best thing is for each person to listen to their own biological clock and lead a well structured life, with regular hours for eating, exercise, entertainment and rest that will help improve our physical and mental health.