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Your body's natural 24-hour rhythm

Published in Sleep Medicine, For the Health of It Author: Troy Payne,MD Author: Troy Payne, MD, FAASM

The average person follows a cycle of around 24 hours — also known as a circadian rhythm.

The term “circadian” means “about a day.” There is a nest of cells deep in the brain called the suprachiasmatic nucleus that keeps the brain clock on the right time. Daily light influences this clock. For most of human history it was dark at night and the sun coming up each morning helped set our internal clocks.

You may not realize it, but the body temperature starts to rise a couple hours before one usually awakens preparing you for your day. Then at night the body temperature falls preparing you for sleep. The pineal gland also produces a surge of melatonin as in gets dark and also helps one feel tired at night.

In Minnesota where it stays light outside very late in June and gets dark very early in December, people are often much more tired in early evening in the winter months but not tired at the same time in summer. As the days get shorter each autumn many people have seasonal affective disorder and develop depression or mood disorders.

We now have light anytime we want. All those light bulbs, laptop computers, gaming systems and cell phones have created the opportunity for us to change our internal clocks. Having a light box present in the room where you are located for half an hour at the same time each morning during the fall and winter can help mood in those with seasonal affective disorder.

However, having bright light from electronics at night shifts the circadian rhythm later. If you go to sleep later because you were playing on your computer or cell phone and then have to get up early for work or school you will not get enough sleep. Insufficient sleep can cause memory problems, a loss of productivity and increased risk of motor vehicle accidents, heart disease, weight gain and diabetes! Getting enough sleep on a regular schedule is very important.

There are some people who through a combination of genetics and lifestyle have a delayed circadian rhythm and are “night owls.” These people do not do well with early morning appointments or occupations. There also are people who have the most energy early in the morning (sometimes called “larks” after an early rising, loud bird) and naturally go to sleep early each evening. When a “night owl” and a “lark” live in the same house it makes for an interesting time scheduling daily family life.