Answer: The amount of sleep you need changes as you age.  A foetus may sleep for up to 16-18 hours day and  a newborn will sleep for 14-16 hours for the first three to six months, with about half of that as dreaming sleep.  As you get older, sleep decreases but with a small increase in adolescence and early adulthood. Young men can sleep for around 10 hours a day, especially if they are very active.  In your 40s it decreases, and by 70 it's down to around six to seven hours a day.

Another change is the quality of sleep.  Around birth, rapid eye movement or dreaming sleep is around 50 per cent, and that continues as the brain develops into early adolescence.  In middle to late adolescence this stabilises around 25 per cent, until old age.  Slow wave "deep sleep" peaks at 20 and starts to decline around 40.

These changes are not inevitable.  Physically active people will maintain high slow wave sleep, or SWS, into late middle age, and early old age.  During SWS, the body is busy repairing the effects of physical activity.  Similarly, mental activity is associated with higher amounts of REM sleep.

Physically and mentally active adults will often have sleep that looks like much younger people.  Older people, who are inactive have less need to recover, experience lighter sleep.  They can go to bed early and rise late to "fill in time".  They spend more time in bed, and more time in bed awake and therefore feel that their sleep is poor.  This is because people judge the quality of sleep based on the amount of time they spend in bed awake.  For many older people, reduced sleep need is due to reduced physical and mental activity and  is exacerbated by more time in bed.

If you want to sleep better as you age, the best thing is stay physically fit.

Response by Professor Drew Dawson, Central Queensland University.

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