Six for 2006: Six reasons not to scrimp on sleep

Content provided by the Faculty of the Harvard Medical School

Six for 2006: Six reasons not to scrimp on sleep

For good health, you need adequate sleep as much as you need regular exercise and a sensible diet. Here’s why.

The National Sleep Foundation and other health organizations have reminded us that we don’t get as much sleep as we used to — or as much as we should — and we’re paying the price in drowsiness and fatigue that affect our physical and mental health and threaten public safety. Despite such warnings, our habits aren’t changing much.

A 2005 National Sleep Foundation survey found that, compared with 1998, more people are sleeping less than six hours a night. Average sleep on work nights is 6.8 hours — still short of a good night’s rest. And sleep difficulties, the poll indicates, visit 75% of us at least a few nights per week. Women are especially affected: They report more trouble sleeping than men do, and they are more likely to feel sleepy during the day.

How serious is the problem? Evidence from the relatively new field of sleep medicine suggests that truncated sleep may contribute to various ills, including memory lapses, trouble learning and paying attention, heart disease, obesity, mood problems, and impaired immunity. Some research suggests a cancer connection.

A sleepless night or two or a short-lived bout of insomnia is generally nothing to worry about. The bigger concern is chronic partial sleep loss — that is, failing to get enough sleep night after night. That can happen because you have a medical condition that interferes with sleep, or perhaps you’ve given up sleep time to accommodate life’s demands. Whatever the case, routine sleep loss can take a toll. Researchers have found that after two weeks, people sleeping four to six hours a night are as cognitively impaired as those who have been awake for two or three days.

How much sleep do we need? Some of us seem to do well with six hours a night, while others need nine or more to feel their best. Judging by clinical impressions, experiments, and research in which subjects are allowed to find their “natural” amount of sleep, experts believe that seven to nine hours is about right. The goal is to wake up feeling refreshed and to stay awake and alert throughout the day without relying on stimulants or other pick-me-ups.

Though more research is needed to explore the links between chronic sleep loss and specific health consequences, it’s safe to say that sleep is too important to shortchange. So in case you haven’t already resolved to get better sleep, here are six reasons to consider doing so.

1. Learning and memory

Sleep helps the brain commit new information to memory by way of a process called memory consolidation. This process came to light largely through experiments in which subjects were trained to complete a cognitive task and later tested. Those who “slept on it” before the test usually did better. In some studies, subjects discovered more insightful or creative ways to problem-solve after a night’s sleep. Research at Harvard has shown that performance on some mental tasks is correlated with the amount of REM (rapid eye movement) or dreaming sleep a subject gets. Other experiments suggest a special role for early-night, non-REM sleep in consolidating memory for facts.

2. Metabolism and weight

It’s well known that excess weight can cause sleep disorders such as apnea. But sleep lab studies also suggest the reverse possibility: Chronic sleep deprivation may cause weight gain. How? By altering metabolic functions, such as processing and storage of carbohydrates, and by stimulating the release of excess cortisol, a stress hormone. Excess cortisol has been linked to increased abdominal fat. Loss of sleep also reduces levels of leptin, a hormone that suppresses appetite, and increases levels of ghrelin (GRELL-in), an appetite-stimulating hormone — a combination that can encourage eating.

3. Safety

There’s no evidence that we ever really adapt to chronic sleep deficits. Sleep debt only contributes to a greater tendency to fall asleep, including “microsleeps” — seconds-long daytime dips into sleep that occur when sleep-type brain-wave activity impinges on the waking kind. These lapses may cause falls and mistakes such as medical errors, air traffic mishaps, and road accidents. The National Highway Traffic Safety Administration estimates that each year, drowsiness causes 100,000 vehicle crashes, resulting in 76,000 injuries and 1,500 deaths.

4. Mood/quality of life

Sleep loss, whether long- or short-term, may result in symptoms — irritability, impatience, inability to concentrate, and moodiness — that suggest psychological problems such as anxiety and depression. Too little sleep can leave you so tired that you don’t want to spend time with your children, enjoy the company of your friends, or have sex with a partner. Poor sleep also affects the ability to work. Sleep disorders such as insomnia and obstructive sleep apnea are associated with depression, although the relationship is complex, and cause and effect are not always clear. One study found that people with obstructive sleep apnea got relief from symptoms of depression when they were treated with a continuous positive airway pressure (CPAP) device, which keeps the airway open and improves breathing during sleep.

5. Cardiovascular health

We don’t know much yet about the effect of chronic partial sleep loss on cardiovascular health. But serious sleep disorders such as insomnia and sleep apnea have been linked to hypertension, increased stress hormone levels, cardiac arrhythmias, and increased inflammation. Sleep apnea is also associated with difficulty metabolizing glucose, which may lead to type 2 diabetes, another significant risk factor for heart disease. In the Nurses’ Health Study, women who slept less than five (or more than nine) hours per night were more likely to develop heart disease than those who slept seven to eight hours.

6. Immunity/cancer prevention

Though all the mechanisms aren’t clear, scientists have found that sleep deprivation alters immune function, including the activity of the body’s killer cells. For example, sleep loss around the time of vaccination for influenza has been shown to reduce the production of flu-fighting antibodies. Keeping up with sleep may also help fight cancer. Harvard researchers have shown that women who work at night are at increased risk for breast and colon cancer. The connection may be through melatonin, a hormone that’s made by the brain’s pineal gland when darkness falls and helps put us to sleep; light at night cuts melatonin production. The Harvard scientists also found that women with low morning levels of melatonin had a higher risk of breast cancer. Other research has shown that melatonin slows ovarian production of estrogen, a hormone that spurs cancer cell growth.

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Last updated:	August 21, 2006