What do the Three Mile Island and Chernobyl nuclear incidents, the Exxon Valdez oil spill and the Dec. 1 , 2013 Metro-North Railroad derailment have in common? Sleep, or rather lack of sleep, was a major contributing factor to each of these events.

It used to be thought sleep was passive, that the brain was simply resting. We now know sleep is an active process. During a good night’s sleep, the brain cycles through several stages, each with its own characteristic brain-wave activity. Despite much research, it is still unclear exactly what the brain is accomplishing during these different stages.

What has been firmly established is that sleep is not a luxury but is essential to good health. Without adequate sleep we cannot function normally, even though people certainly try, often with disastrous consequences. For example, last year alone people drowsy from insufficient sleep were responsible for about 100,000 automobile accidents.

Most adults need about 7 to 8 hours of sleep and do best with a regular sleep-wake cycle that enables them to be awake during daylight. Unfortunately, there are endless problems that may interfere with this objective.

An uncomfortable bedroom temperature, excess noise, even a partner who snores can all interfere with sleep. Caffeine, alcohol and tobacco use commonly contribute to sleep difficulties. Many diseases, especially if associated with pain, may also interfere.

People who work evening and night shifts are especially at risk for sleep problems. Workers who rotate among different shifts can never establish a healthy sleep cycle. Even those who work a regular night shift frequently have difficulty maintaining a normal cycle.

Teenagers are notoriously sleep deprived; it’s just about impossible to get one to go to sleep at a reasonable hour. Many schools are experimenting with starting later in the morning so that students will have enough time for a good night’s sleep.

advertisement | advertise on newsday

The medical profession has a long history of disregarding the issue of sleep. Until recently, working frequent 24-hour shifts was a rite of passage for doctors-in-training. There are now rules limiting how many hours a doctor-in-training may work and mandating sufficient time off for sleep. Interestingly, there are no rules that limit the number of hours fully trained doctors can work. For example, it is still the norm for anesthesiologists to frequently work 24-hour shifts.

And of course there is daylight saving time: guaranteed to make sure everyone’s sleep cycle is disrupted at least twice a year.

Dr. Stephen Picca of Massapequa is Board Certified in both Internal Medicine and Anesthesiology. He is retired from practice. Questions and comments can be sent to Dr. Picca at health@newsday.com.