At the center of health and well-being is good sleep. We need sleep to rejuvenate our bodies, to boost our immune system, and to consolidate short-term memories into long-term ones. We need it for the release of human growth hormone and for the brain to clear out harmful toxins. Without sleep, our mood, energy, and mental alertness are compromised and we cannot function at full speed.
But if you wake up drowsy or simply enjoy luxuriating in the morning on your new favorite mattress, you may find yourself wondering just how much sleep we need—and how much sleep is too much.
The National Sleep Foundation can answer that. While everyone’s individual sleep needs vary, most adults 18 years and over need between seven and nine hours of sleep each night.
Serious Health Issues Can Occur
Most experts agree that more than nine hours is excessive, and, in fact, excessive sleep on a regular basis may be detrimental to a person’s health. An analysis of 74 studies that involved more than 3 million people found that sleep outside the parameters of seven to eight hours—both fewer and additional hours of sleep—is associated with cardiovascular problems and increased risk of death. The greater the deviation from the recommended seven to eight hours’ sleep, the greater the risk.
Diabetes is another concern. While the link between lack of sleep and Type 2 diabetes is well established, a recent study by the University of Chicago involving nearly 1,000 adults who had prediabetes or newly-diagnosed, untreated Type 2 diabetes showed that participants who slept more than eight hours a night on average (or fewer than five hours) had poorer blood glucose control than those who slept between seven and eight hours.
We know that memory is distorted when we sleep poorly, but the same goes when you get too much sleep. The Nurses’ Health Study, one of the largest studies into the risk factors for major chronic diseases in women, found that participants who slept nine hours or more each night (or five hours or fewer) performed worse on memory and thinking tasks compared to those who slept seven to eight hours a night.
At the very least, Harvard Medical School reports, too much sleep may zap your energy. That seems contradictory, but by getting more sleep than is typically recommended, your body’s circadian rhythm becomes conflicted.
Our circadian rhythm regulates the timing of when we sleep and when we awaken. The circadian rhythm, in turn, is controlled by the suprachiasmatic nucleus (SCN), a part of the brain that responds to light. When our eyes register light in the morning, it signals to the SCN that it is time to wake up, and sets in motion several actions—including a rise in body temperature and the release of hormones, such as cortisol, which play a role in making us feel alert. Oversleeping disrupts this process, leading to a feeling of fatigue much like jet lag.
However, oversleeping may be a red flag for several existing health issues, especially if you do not feel refreshed when you wake up. For example, obstructive sleep apnea is a serious disorder where a person stops breathing momentarily on and off throughout sleep. It’s typically caused because, in deep sleep, the throat’s muscles relax—and for some people, this can block their airway.
Loud snoring may be a sign a person has sleep apnea. Other symptoms include morning headaches, a dry throat in the morning, excessive daytime sleepiness, difficulty concentrating, and altered mood. If you suspect you may have sleep apnea, it is advisable to consult a sleep specialist.
Another sleep disorder is narcolepsy, which is characterized by excessive daytime sleepiness and involuntary episodes of falling asleep during the day. It may also cause hallucinations, cataplexy (where strong emotions and laughter cause sudden muscle weakness or paralysis), or sleep paralysis (temporary inability to move or speak when passing through the stages of wakefulness and sleep). These episodes generally last from a few seconds to a few minutes.
Oversleeping can also be a sign of depression. An estimated 40% of young adults with depression experience oversleeping, while the figure is more like 10% for older adults, with a prevalence among women.
What You Can Do
Regardless as to why you might be oversleeping, keeping the status quo may not be doing your physical or mental health any favors. Spending an excessive amount of time in bed is linked to health risks, so getting the much-touted seven to eight hours of sleep a night is sound advice.
Need help waking up? Check out our ranking of the Best Alarm Clocks.