Lack of sleep adds to risks of cancer and obesity

Japanese have less sleep as compared with other peoples in the world. According to a survey of 29 countries conducted in 2014 by the Organization for Economic Cooperation and Development (OECD), the average amount of time Japanese spent sleeping was seven hours and 43 minutes. They placed 28th, only one notch above bottom-ranked South Koreans who slept an average seven hours and 41 minutes. Now how does a lack of sleep affect human mind and body?

First, it has become known that insufficient sleep can raise cancer risk. A follow-up survey on 22,000 males conducted in 2008 by Tohoku University showed that the incidence rate of prostate cancer for those who slept less than seven hours per day was 1.38 times higher than that for those who slept for seven to eight hours. The survey cited a weakened immune system caused by lack of sleep as the main culprit. Generally, people develop cancer when cancer cells generated by gene mutation multiply for some reason or other. Normally immune cells kill cancer cells to prevent the disease developing. However, when the function of immunity is weakened due to lack of sleep, cancer cells have more chances of surviving and growing rather than being killed. Moreover, lack of sleep can make people more susceptible to obesity.

A health and nutrition survey by Columbia University in New York has revealed that the less people sleep, the higher their risk of obesity becomes. The research said that people who sleep less than four hours are 73% more likely to develop obesity than those who sleep seven to nine hours. It traced the main cause to collapse of the hormone balance.

Appetite is controlled by hormone ghrelin which promotes it and hormone leptin which holds it down. However, when people do not have enough sleep, ghrelin tends to increase whereas leptin decreases. Stresses resulting from sleeplessness can also be a cause of obesity.

Sleep is closely related to people’s happiness. According to the “World Happiness Report 2017” announced by the Sustainable Development Solutions Network (SDSN), a joint scheme of the United Nations and Columbia University, Japan ranked 51st in “Subjective Happiness Scale” among the world countries. Its ranking was quite low, actually the lowest among the G7 countries and 27th among the 35 OECD member countries. The above OECD survey made it clear that people in Scandinavian and European countries, which ranked higher in the happiness scale, had longer sleep than Japanese. It supports a solid fact that a sufficient amount of sleep is inevitable for people to feel happy.

All the data seen above clearly tell that lack of sleep can cause various adverse effects. A mentally and physically rich life indeed requires enough amount of sleep.

(Written by: Yuta Uchino)


まず、睡眠不足はがんのリスクを高めることが明らかになっている。 東北大学が2008年に2万2000人の男性を対象に行った追跡調査によると、睡眠時間が7時間未満の男性は7~8時間の人に比べ、前立腺がんの発症率が1・38倍高かった。睡眠不足が免疫力を低下させることが原因だった。そもそも、がんは遺伝子の突然変異によって生まれるがん細胞が増殖することで発症するが、通常であれば免疫細胞によって死滅させられる。しかし睡眠不足によってこの免疫細胞の機能が低下していた場合、がん細胞は死滅せず増殖してしまう可能性が高くなるというのである。さらに、睡眠不足によって肥満になりやすくなる。







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