Middle-aged adults who sleep less than six or more than eight hours a night are more likely to experience a decline in brain function. The magnitude of that mental decline is equivalent to four to seven years of ageing.
There is an expectation in today’s 24-hour-a-day society that people should be able to fit more into their lives. The whole work/life balance struggle is causing people to trade in precious sleeping time to ensure they complete everything they feel is expected of them. This study suggests that this may have adverse effects on their cognitive function.
Adequate, good quality sleep is fundamental to human functioning and well-being. Sleep deprivation and sleepiness have adverse effects on performance, response times, errors of commission, and attention or concentration. Furthermore, sleep duration has been found to be associated with a wide range of quality of life measures, such as social functioning, mental and physical health, and early death.
Since most research has focused on the effects of sleep deprivation on biological systems, it is not yet fully understood why seven hours is optimal – or why long sleeping appears to be detrimental. Chronic short sleep produces hormones and chemicals in the body, which increase the risk of developing heart disease and strokes, and other conditions like high blood pressure and cholesterol, diabetes and obesity.
Researchers from England collected data on 5,431 men and women, aged 35 to 55 years in 1985, who took part in a long-term look at London-based office staff known as the Whitehall II study. In 1997-1999, the participants were asked how many hours they slept on an average week night, and were asked the same question in 2003-2004 after an average 5.4 years of follow-up. Those who reported changes in their sleep patterns were then compared with people whose sleep duration stayed the same over the course of the study. In 2003-2004, each individual was given a battery of standard tests to assess his or her memory, reasoning, vocabulary, global cognitive status and verbal fluency.
The researchers found that during the study, 58 percent of men and 50 percent of women continued to sleep the same amount each night. However, 7.4 percent of women and 8.6 percent of men increased their slumber from seven to eight hours per night. This change in sleep pattern was associated with lower scores on six tests of cognitive function, compared with people whose sleep time did not change, it was found. Only scores on the test of short-term verbal memory were not affected by sleeping more. In addition, some 25 percent of women and 18 percent of men reported decreases in their sleep – dozing less than six, seven or eight hours per night. This change was associated with lower scores on three of the six cognitive tests, with lower scores on the reasoning, vocabulary and global cognitive status tests, the researchers said. Surprisingly, increasing sleep from six hours or less had no beneficial effect.
Getting enough sleep helps many brain functions. It is restorative; it lets you concentrate better and process new information better and faster. It is not clear why too much sleep is unhealthy but it may be a sign of other health problems. To stay healthy, sleep is as important as eating well and being physically active, the researchers conclude.
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