Unmet sleep needs of the elderly elevate their risk of memory loss and a wide range of mental and physical disorders, says a study.

The researchers, however, warned that the pills designed to help us doze off are a poor substitute for the natural sleep cycles that the brain needs in order to function well. "Don't be fooled into thinking sedation is real sleep. It's not," said the study's senior author Matthew Walker, Professor at the University of California, Berkeley in the US.

Restorative, sedative-free slumber can help ward off mental and physical ailments, said the review article published in the journal Neuron. "Nearly every disease killing us in later life has a causal link to lack of sleep," Walker said.  "We've done a good job of extending life span, but a poor job of extending our health span. We now see sleep and improving sleep, as a new pathway for helping remedy that," Walker noted.

Unlike more cosmetic markers of ageing, such as wrinkles and grey hair, sleep deterioration has been linked to such conditions as Alzheimer's disease, heart disease, obesity, diabetes and stroke, he said.

Though older people are less likely than younger cohorts to notice and/or report mental fogginess and other symptoms of sleep deprivation, numerous brain studies reveal how poor sleep leaves them cognitively worse off. Ageing brain has trouble generating the kind of slow brain waves that promote deep curative sleep, as well as the neurochemicals that help us switch stably from sleep to wakefulness, the study found. 

Of course, not everyone is vulnerable to sleep changes in later life. "Just as some people age more successfully than others, some people sleep better than others as they get older, and that's another line of research we'll be exploring," said lead author Bryce Mander from the University of California, Berkeley.