A new study has shown that poor sleep as a person reaches middle age could mean that the brain is prematurely ageing, equivalent to a decline of up to seven years.
The study included more than 5,400 people aged 45-69 and the researchers found that there was significant decline in brain power in those people who had, over the course of a five-year period, changed the amount they slept from the optimum six to eight hours per night.
Jane Ferrie of the department of epidemiology and public health at University College London Medical School, who led the study said, “The main result to come out of our study was that adverse changes in sleep duration appear to be associated with poorer cognitive function in later middle age.” The results are published in the 1 May edition of the journal Sleep.
The researchers asked all the participants about their sleeping habits in 1997-1999 to establish baseline numbers and again in 2002-2004 for a follow-up. Their cognitive functions were monitored using a range of tests that included measurements of memory, vocabulary and reasoning. They also carried out the mini mental state examination, designed to test for the early signs of dementia.
Their queries revealed that women who slept for about seven hours a night and men who slept for six to eight hours scored the highest. Sleeping much less than six hours or much more than eight was associated with lower scores of cognition researchers found.
The researchers then looked at how people's sleep patterns had changed. At the time of the follow-up in 2002-2004, 7.4% of the women and 8.6% of the men said they had increased the amount they had been sleeping compared with their baseline amounts in 1997-1999. When compared with people whose sleep patterns had not changed since their baseline, those who had been sleeping more showed lower scores on five of the six cognitive function tests. Only memory was left unchanged. In 25% of the women and 18% of men, the amount of sleep had dropped significantly from their baseline figures. These people had lower scores in reasoning, vocabulary and global cognitive tests.
This was a part of the Whitehall Study II, which has followed more than 10,000 British civil servants since 1985 to investigate how health is affected by social conditions.
“Almost all the experimental work that's being done in sleep laboratories is all about sleep deprivation,” Ferrie said. “But when we look at disease outcomes, when we look at mortality and now, cognitive function, which is the first time anyone's done this, it's the long end of the sleep distribution that seems to be the most harmful.” It's not clear why. One theory is that people who report long hours of sleep have fragmented sleep, Ferrie said. “They're actually in bed and sort of asleep for quite a long time, but they don't have the benefit of the deep sleep, which is the bit that's really restorative.” People suffering from depression also tend to sleep more, and depression itself has been associated with worse cognitive function. Sleep as a healthy behaviour has been neglected too long, Ferrie said. “We see a lot about alcohol, we see a lot about smoking. We see not anywhere near as much about sleep in terms of health promotion.”
Researchers concluded that good quality sleep is important for proper functioning and wellbeing. Too much sleep has also been linked to early death. “The detrimental effects of too much, too little and poor quality sleep on various aspects of health have begun to receive more attention…Given that our 24/7 society increasingly impinges on the lives of many people, it is important to consider what effects changes in sleep duration may have on health and wellbeing in the long term,” said Ferrie. Researchers said that the ideal amount of sleep duration of seven hours per night resulted in the highest score for every cognitive test.
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