Too much or too little sleep can boost your risk of death, British researchers report.

“In terms of prevention, our findings indicate that consistently sleeping seven or eight hours a night is optimal for health,” study author Jane E. Ferrie, of University College London Medical School, said in a prepared statement.

Her team studied more than 8,000 people, aged 35 to 55, who were followed for a number of years.

Among participants who slept six, seven or eight hours a night at the start of the study, a decrease in nightly sleep duration was associated with a 110 percent excess risk of cardiovascular-related death.

Similarly, among those who slept seven or eight hours per night at the start of the study, an increase in nightly sleep duration was associated with a 110 percent excess risk of non-cardiovascular death.

The study appears in the Dec. 1 issue of Sleep.

On average, most adults need seven to eight hours of sleep per night to feel well-rested and alert, according to the American Academy of Sleep Medicine.

Sleep deprivation can lead to serious health risks both mentally and physically. Not getting enough sleep can lead to depression, irritability, mood swings, cardiovascular disease, slower reaction times, impaired concentration, impaired decision making, decreased test scores, impaired immune system, and more.

Sleep deprivation affects millions of Americans and as with most things, our ability to get quality sleep decreases as we age. In the following article from the New York Times avoiding caffeine, drinking milk before bed time, and other lifestyle changes are not the only ways to increase ones quality of sleep.

Studies have found that in general, the optimal temperature for sleep is quite cool, around 60 to 68 degrees Fahrenheit. For some, temperatures that fall too far below or above this range can lead to restlessness.

Temperatures in this range, it seems, help facilitate the decrease in core body temperature that in turn initiates sleepiness. A growing number of studies are finding that temperature regulation plays a role in many cases of chronic insomnia. Researchers have shown, for example, that insomniacs tend to have a warmer core body temperature than normal sleepers just before bed, which leads to heightened arousal and a struggle to fall asleep as the body tries to reset its internal thermostat.

For normal sleepers, the drop in core temperature is marked by an increase in temperature in the hands and feet, as the blood vessels dilate and the body radiates heat. Studies show that for troubled sleepers, a cool room and a hot-water bottle placed at the feet, which rapidly dilates blood vessels, can push the internal thermostat to a better setting.