Every year on the last Sunday in October, clocks go back in the UK at 2am, signaling the start of shorter days.

This year the clocks will go back one hour at 2am on Sunday October 27th, giving us an extra hour in bed as we prepare for the colder winter months.

While most of us welcome an extra hour of sleep, the system of changing clocks twice a year can be controversial due to health and behavioral concerns related to changing sleep habits and adapting to darker evenings. Some studies have also shown that it disrupts the body’s natural sleep cycles, which can impact both physical and mental health.

What effects does turning back the clocks have on our health?

How does changing the clock affect physical health?

The human brain has a biological clock, also called circadian rhythm, which runs in a 24-hour cycle.

Whether sleeping an hour more or sleeping an hour less disrupts their sleep cycles and can make it difficult for some people to readjust to a normal sleep schedule. Disturbed sleep could also potentially lead to a higher risk of cardiovascular disease.

A 2019 study by researchers at Harvard Medical School and Massachusetts General Hospital examined the effects of sleep loss on heart disease in mice. It found that mice whose sleep cycles were disrupted developed larger arterial plaques after 16 weeks compared to mice with normal sleep patterns.

The sleep-deprived mice also had double the proportion of certain white blood cells in their circulation and lower levels of hypocretin, a hormone that plays a key role in regulating sleep and wakefulness.

“This appears to be the most direct evidence to date of the molecular connections linking blood and cardiovascular risk factors to sleep health,” said Dr. Michael Twery, director of the National Center on Sleep Disorders Research at the National Heart, Lunch and Blood Institute in the USA.

Losing an hour of sleep during the spring time change has been linked to an increase in heart attacks and strokes. In the United States, hospitals report a 24 percent increase in heart attack visits each year on the Monday after the clocks go forward.

Research has also shown that car accidents increase when clocks go back in the colder months as drivers adjust to the time change.

According to data from Zurich Insurance, the risk of accidents for drivers is higher between 4 p.m. and 7 p.m. in November because the evenings get darker earlier. After the time change, the company recorded a 10 to 15 percent increase in the number of accidents during this time compared to the rest of the day.

How does changing the clock affect mental health?

When the clocks go back in the fall, we get an extra hour of daylight in the morning – although this only lasts a few weeks before the days get shorter and the sunrise gets later and later.

On the shortest day of the year, December 21st or 22nd, the UK enjoys less than eight hours of sunlight.

The prolonged darkness can cause low mood and depression in some people, as well as fatigue, muscle pain and weakened bones due to vitamin D deficiency from sun exposure.

Some people also suffer from seasonal affective disorder (SAD) due to the shorter days. According to the NHS, SAD symptoms include persistent low mood, loss of interest in normal everyday activities, irritability, feelings of despair or guilt, and sleeping longer than normal.

The health department says the lack of sunlight can cause a part of the brain called the hypothalamus to not function properly, affecting the production of melatonin (a sleep hormone) and serotonin (a mood hormone), as well as the body’s circadian rhythm can .