[Special Feature: Japanese "Resting Styles"] What is Good Sleep?

2019/04/05

In modern society, it is said that one in five people suffers from insomnia, and one in 20 takes sleeping pills. The rate of insomnia is said to increase particularly with age, and in our country, where the population is aging rapidly, sleep disorders among the elderly are on a continuous upward trend.

According to the summary of the 2015 National Health and Nutrition Survey by the Ministry of Health, Labour and Welfare, the percentage of people sleeping 7 hours or more is 18.3% for men and 14.4% for women aged 50–59. For those aged 70 and over, these figures rise to 47.6% for men and 39.2% for women, representing an increase of 2.6 times for men and 2.7 times for women. In a 2010 survey on psychotropic drug prescriptions using medical fee data from the Ministry of Health, Labour and Welfare, the prescription rate for sleeping pills was 3.6% for men and 5.2% for women aged 55–59. However, for those aged 65 and over, it rose to 7.6% for men and 10.6% for women, doubling the prescription rate for both genders.

The rapid increase in sleeping pill prescription rates is not seen in age groups under 60 and is specific to sleeping pills and anti-anxiety medications; such trends are not observed for antidepressants or other psychotropic drugs. While the causal relationship has not been investigated in detail, it is possible that upon reaching retirement age at 60–65, people are able to secure sufficient sleep time at home, leading to a sudden extension of sleep duration. In actual clinical settings, we often see cases where people spend more time at home after retirement, reducing mental and physical burdens. This lifestyle, free from excessive fatigue, leads to longer sleep times and shorter wake times, which reduces the drive for sleep and results in insomnia.

On the other hand, under the author's supervision, we analyzed the relationship between sleep duration and BMI (Body Mass Index) using wrist-worn sleep monitors and identified the "sleep duration most conducive to weight loss" (Figure). As a result of this survey, the relationship between sleep duration and BMI values revealed that people with "7 hours of sleep" had the lowest average BMI. To maintain a body that loses weight easily, sleep duration should be neither too short nor too long; the best duration was found to be 7 hours.

When averaging BMI values by sleep duration, it was found that men sleeping "7 hours" or "7 hours 30 minutes" and women sleeping "7 hours" had the lowest BMI values. Meanwhile, looking at the number of people per sleep duration category, the most common duration was "6 hours" for men and "6 hours 30 minutes" for women. With these as the peak, the number of people gradually decreased as sleep became longer or shorter. To achieve sleep that aids weight loss, it was found that men should aim for an additional hour and women an additional 30 minutes of sleep.

According to several large-scale surveys conducted in the US and Japan, people who sleep 7 hours have the highest probability of being alive six years later. Japanese people often tend to go to extremes in all matters, and as a result of work-style reforms, there is a possibility of shifting from "extreme overworking" to "extreme over-resting."

From these results, it was found that for the senior generation reaching retirement, not exceeding 7 hours of sleep is key to suppressing the use of sleeping pills. For the working generation who wish to prevent obesity—a cause of lifestyle-related diseases—it is important to secure 7 hours of sleep as much as possible. Rather than believing in extreme sleep management, please remember that "the benchmark for good sleep is 7 hours."

When I opened the Sleep Clinic in Chofu 14 years ago, patients flooded in from all over the country, leading to expansions in Ginza, Aoyama, and Sapporo, as well as the establishment of a sleep outpatient clinic within Keio University Hospital in Shinanomachi. The reason patients flock to us is the "actigraph" I developed. By simply wearing this device—about the size of a 500-yen coin—on the waist, one can track daytime activity levels, calories burned, timing of sleep onset, sleep quality, posture, and even the presence of tossing and turning. Moderate daytime activity is also important for getting good sleep, and this can be easily monitored with the actigraph.