How much do I need to sleep? It depends on your age

Do you find yourself dozing off at your desk, even after what you thought was a good night's rest? Then you probably have the same question as so many others: How much do I need to sleep?

The answer of how many hours you need is not so straightforward, said Dr. Raj Dasgupta, an assistant professor of clinical medicine in the division of pulmonary, critical care and sleep medicine at the Keck School of Medicine of the University of Southern California.

Sleep needs are very individualised, he said, but the general recommendation -- the "sweet spot" -- is to get seven to nine hours of sleep a night. Recommendations really change as people age, however.

"Sleep needs vary over the lifespan," said Christina Chick, a postdoctoral scholar in psychiatry and behavioral sciences at Stanford University.

Adults should get at least seven hours of sleep a night, but 1 in 3 of them don't, according to the US Centers for Disease Control and Prevention.

Poor sleep has been associated with long- term health consequences, such as higher risk of cardiovascular disease, diabetes, obesity and dementia. In the short term, even one day of sleep loss can harm your well-being, according to a recent study. People who get poor sleep might also be predisposed to conditions such as anxiety, depression and bipolar disorder, Dasgupta said.

"There are chronic consequences, and there are acute consequences, which is why sleep is more than just saying, 'The early bird gets the worm,'" he said. "It's much more than that."

If it feels like babies are sleeping all day, they pretty much are. In the first year of life, babies can sleep 17 to 20 hours a day, Dasgupta said. Infants 4 months to 12 months need their 12 to 16 hours of sleep, including naps, according to Chick.

Toddlers, who are between the ages of 1 and 3, should get 11 to 14 hours of sleep, according to Dr. Bhanu Kolla, associate professor of psychiatry and psychology at the Mayo Clinic with a special interest in sleep. Children ages 3 to 5 should sleep for 10 to 13 hours, he added, and from ages 6 to 12, they should sleep nine to 12 hours. For kids up to age 5, these sleep recommendations include naps, Chick said.

Teenagers should get eight to 10 hours of sleep, Kolla said. This recommendation has sparked a debate in recent years about start times for school.