THE DETAILS: A look at some powerful statistics illustrates the importance of sleep for good mental health. Over the past 50 years, the rate of depression has been doubling every decade. During that same time period, Americans have been sleeping progressively less, so that today we are sleeping about an hour less per night than we did 50 years ago. (A National Sleep Foundation survey found the current average for adults to be 6 hours and 40 minutes.) The correlation between less sleep and more depression is not a coincidence. Prolonged sleep deprivation can cause mood disturbance. For many years the prevailing psychiatric wisdom was that depression caused problems with sleep. Today we know from longitudinal studies that the opposite is also true. Sleep problems frequently precede the development of depression or another mood disorder.
There are physiological reasons why this is so. A study done by Carlos Pirola, PhD, at the Universidad de Buenos Aires, in Argentina, found that night-shift workers had significantly lower levels of the neurotransmitter serotonin than day-shift workers. Low serotonin levels are associated with anxiety, irritability, and depression. This finding helps to explain why night-shift workers are more prone to depression. Having worked the night shift at a hospital in my early 20s, I can tell you there is a reason they call it the graveyard shift. Another study, led by Matthew Walker, PhD, of the University of California, Berkeley, published in the journal Current Biology, sheds light on how sleep deprivation changes brain function and leads to disturbed mood. Walker studied 26 healthy students ages 24 to 31 who had either stayed awake all night or had gotten a full night's sleep. Their brain activity was monitored by functional magnetic resonance imaging (MRI) while they observed a series of 100 photos that became increasingly disturbing as they progressed. The early pictures were images of a wicker basket on a table. Subsequent photos were increasingly disturbing, such as a large spider on a person's shoulder, and finally, slides of burn victims and other emotionally distressing pictures.
When the pictures were more emotionally charged, the sleep-deprived subjects displayed 60 percent greater activity in the amygdala, a midbrain structure that decodes emotional experience. Walker reported the magnitude of the difference in the sleepless group to be "profound," greater than the difference he had seen for any group he had studied. Walker's team also looked at which brain regions were communicating with one another. In the well-rested subjects the amygdala seemed to be speaking with the medial prefrontal cortex, an outer layer of the brain that enables us to think about our emotions and put them in context. In the sleep-deprived subjects, however, the amygdala seemed to be "rewired," communicating instead with a brainstem region called the locus coeruleus, which secretes norepenephrine, a precursor of adrenaline, which triggers the fight-or-flight response.
WHAT IT MEANS: These two studies provide physiological explanations of how sleep deprivation contributes to problems with mood. Without sleep, the amygdala, the brain's emotional processing center, is more reactive to uncomfortable emotional stimulation. Without the emotional regulation provided by the medial prefrontal cortex, the amygdala can hijack the brain and the body, causing heightened anxiety and irritability. If sleep deprivation is prolonged, neurotransmitters that influence mood—such as norepinephrine and serotonin—can become depleted, leading to depression.
Sleep is a remedy that doesn't require a prescription, doesn't cost money, and is free of unpleasant side effects. But sometimes we have trouble taking advantage of it. So here are some recommendations are for those of you who are not giving yourselves enough time for sleep. Next week, I will be sharing tips for how to get a better night's sleep if you already give yourself enough time but have trouble getting to sleep or staying asleep.
• Assess your sleep deficit. According to the National Sleep Foundation, there's no magic number for how many hours of sleep you need. In fact, sleep needs are very individual. There are a number of ways to tell if you are not getting enough sleep: you don't awaken feeling refreshed in the morning, you can't wake up without an alarm clock, you conk out—exhausted—as soon as your head hits the pillow, or you get sleepy or doze off during the day or evening. If you experience any of these indicators, take steps to give yourself adequate time to sleep.
• Stick to your bedtime. Try to avoid staying up later than your regular bedtime whenever possible. Some late-evening events are unavoidable, but many of the reasons we stay up late are elective. Watching TV, using the computer, and talking on the phone are definitely in the elective category.
• Plan around your sleeping schedule. If you travel a lot, try to choose flights that are less likely to interfere with your normal sleep rhythm. If you are flying across time zones, keep your sleep needs in mind as you arrange your travel and activity schedule. If your work schedule interferes with your sleep, do something to change it; if you can't, reschedule the other parts of your day to make sure you get enough sleep.
• Make it a family priority. If you have young children who wake you up during the night, do your best to help them learn to sleep in their own beds. Easier said than done, I admit. But the time and effort you invest now will pay dividends in better sleep, mood, and health for you and your child.
• Follow a ritual. Develop a regular relaxing bedtime routine that enables you to wind down and get into bed at your desired bedtime. Your routine might include a hot shower or bath, herbal tea, and relaxing activities such as reading or watching TV. Get your television-watching and Internet use out of the way early, if you can; some research suggests they make it harder to fall asleep.
• Take naps. If you are sleepy during the day, and your schedule allows it, take a nap. The rest will reenergize you, and it counts toward meeting your overall sleep requirement. The only reason to avoid napping is if you are having trouble getting to sleep at night. See our How to Nap story for details.
You can learn more about getting adequate sleep by visiting the website of the National Sleep Foundation, sleepfoundation.org.
Jeffrey Rossman, PhD, is a Rodale.com advisor and the director of life management at Canyon Ranch in Lenox, MA. His column, "Mind-Body-Mood Advisor," appears Mondays on Rodale.com.