by Karin Zeitvogel

SAN DIEGO, California, Feb 21, 2010 (AFP) - What starts with an "s" that seniors need more of than younger adults, is great to get a bit of in the middle of the day and could cause teens to turn to drugs if they don't get enough of it?

The answer is sleep, according to several studies presented at the annual meeting of the American Association for the Advancement of Science.

A study conducted by researchers at the University of California San Diego (UCSD) found that 68-year-old adults, on average, did better on a simple memory test if they got more sleep.

In younger adults, aged 27 years on average, the quality of sleep also affected how they performed on the same test.

"What mattered in the younger adults was sleep efficiency - that the sleep was consolidated into one solid chunk," said Sean Drummond, a professor at UCSD's department of psychiatry who led the study, adding that sleeping soundly and uninterruptedly happens less and less frequently with age.

"The most common change in sleep as we age is you wake up in the middle of the night and you're awake for some time, meaning you have lower sleep efficiency," Drummond said.

"In the older adults what we found is that waking up in the middle of the night did not affect brain function or performance the next day but if a young adult did that, it had significant detrimental effects on brain function," he said.