Better sleep better brains

Title Change in sleep duration and cognitive function: Findings from the Whitehall II study
Authors Ferrie JE, Shipley MJ, Akbaraly T, Marmot MG, Kivimäki M, Singh-Manoux A

Sleep 2011;34:565-573

Media coverage The study has attracted widespread coverage in the press including the Daily Telegraph, Guardian and BBC Woman’s Hour, among many others.
Lay summary

The length of time we sleep normally decreases as we age, so does cognitive function. However, hardly any research has examined whether change in sleep over time is associated with poorer cognitive function.

The study used data from 5,431 people taking part in the on-going Whitehall II study. Sleep duration on an average week night was measured during Phase 5 (1997-1999) and Phase 7 (2003-2004) and cognitive function was measured using 6 standard tests at Phase 7.

7.4% of women and 8.6% of men reported sleeping for longer than the 7-8 hours they reported at Phase 5. In comparison with participants whose sleep duration had not changed, this increase in sleep duration was associated with lower scores at follow-up on five out of six cognitive function tests. On the other hand, 25% of women and 18% of men reported sleeping for less than the “6, 7, or 8 hours” reported at Phase 5. This shift was also associated with a decline in cognitive function. For women, 7 hours of sleep per night was the most beneficial in terms of cognitive function, while for men, 6-8 hours was optimal.

These findings suggest that women and men who begin sleeping more or less than 6-8 hours per night are subject to an accelerated cognitive decline that is equivalent to four to seven years of ageing.

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