If you doze off during the day, an earlier bedtime could protect your health.

RODALE NEWS, LENOX, MA—Did you find it particularly difficult to get out of bed this morning, now that the holiday weekend is over and you're back to a regular schedule? The importance of sleep goes beyond keeping you well-rested for a busy week. If you are one of the estimated 50 million Americans who are sleep-deprived, you're missing out on one of the easiest ways to protect your mood and your health by not getting to bed a little earlier. I know this seems ridiculously obvious. But it is remarkable how many people suffer from irritability, anxiety, or depression that could be remedied with better sleep. I frequently speak with people who are suffering from fatigue, low mood, and trouble concentrating simply because they don't give themselves enough time to sleep. And though those immediate benefits alone are plenty of reason to make sure you get the sleep you need, there are even bigger health issues at stake. Chronic sleep deprivation has also been linked to the development of obesity, impaired immunity, heart disease, and several kinds of cancer.

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.