Most of us seriously underrate the importance of sleep when it comes to our health. For many, it’s an imposition, stealing valuable time that could be filled with work or play. For those with sleep problems, the bed can be a torture chamber of restless nights and wide-eyed staring at the alarm clock.

In reality, restful sleep is a cornerstone of good health. Deep or “core” sleep, the first two to four hours, is when the body repairs itself, ensuring the health of the immune system, neurological functions, and tissue. This is followed by rapid eye movement, or REM sleep, when the brain takes the information gathered throughout the day and “files” it into various categories, storing vital long-term memory and discarding unnecessary short-term data.

If you don’t get enough restful sleep, both core and REM, the body can experience physical problems, while the mind can get foggy. In the short term, the most common symptoms are forgetfulness and lack of concentration; in the longer term, sleep problems can be linked to heart disease, diabetes, depression, and even difficulty shedding excess weight. If you like to brag to people about how little you sleep, spending that time cramming in other activities instead, you may want to rethink it: eventually, it will catch up with you. You can’t “bank” sleep hours; your body needs between six and nine hours of restful sleep each night for optimum health.

Occasional sleeplessness isn’t cause for concern, especially if you can pinpoint the reason for it, such as a particularly stressful day. It becomes a problem when symptoms go on for longer periods: a long time to fall asleep, waking up throughout the night, difficulty concentrating, irritability or emotional outbursts, fatigue, or sleepiness during the day. If such symptoms last for a month or more, doctors usually consider it to be chronic insomnia.

Sleeplessness is a symptom, and the key to overcoming it is in understanding what is causing it. In some cases, the underlying reason is external and relatively easy to fix: the bedroom is too hot, too cold or not dark enough, a partner is snoring, or a pet allowed to sleep on the bed gets up and down throughout the night. A sedentary lifestyle may also be to blame: in simple terms, the body isn’t sufficiently tired. Regular exercise improves the quality of sleep, providing it isn’t done too close to bedtime.

In many cases, insomnia is caused by underlying medical problems, which is why paying attention to your overall health is important. It’s easy to get into a vicious circle: poor health habits cause sleeplessness, which in turn leads to more health problems, which in turn make the insomnia worse. The time to fight insomnia is long before it ever becomes a problem. It may sound simplistic, but watching your weight, quitting smoking, eating properly, and getting the right blend of vitamins and minerals will help ensure your overall health, which in turn will help ensure the quality of your sleep. And, in another circle, that restful sleep will in turn help to keep you healthy.