It’s no secret that not getting enough sleep is bad for your health. It depresses immune function and wound healing, affects your mood and mental health, and raises the risk of a host of chronic diseases.
But did you know that sleeping too much may have many of the same effects?
Researchers consider seven to nine hours of sleep a night to be the healthy range; less than seven hours is considered undersleeping, while more than nine hours is considered oversleeping. Only about 2 percent of the population actually need more than nine hours of sleep a night, and most have been that way since childhood.
For both under- and oversleeping, the health effects only show up over the long term. So you don’t have to worry if you pull an occasional late night or if you sleep in sometimes on the weekend. But regularly sleeping more than nine hours or feeling unrested unless you get more sleep than that could be cause for concern.
In many cases, oversleeping is simply a symptom of an underlying physical or mental health problem. But some evidence suggests that oversleeping might also be a direct cause of other health problems.
Is too much as bad as too little?
Numerous studies have shown that getting too little and too much sleep tend to have the same effects. Among the effects shown by not getting the right amount of sleep are an increased risk of obesity, diabetes, heart disease and stroke. Perhaps for this reason, people who sleep too little or too much have dramatically lowered longevity relative to people who get seven to nine hours a night. Too much sleep also appears to impair fertility.
People who sleep too much also show increased inflammation, suggesting immune dysfunction and an increased risk of chronic disease. Getting too much sleep also causes people to perform worse on tests of memory and cognitive function, similar to the effects of too little sleep. These effects might be short-term, or they might foretell worse to come: too much sleep has also been linked to increased risk of Alzheimer’s disease.
Sleeping too much is also linked with increases in back pain, headaches and migraines. There is even a term for a migraine or tension headache triggered by too much sleep: a “weekend headache.” In this particular case, researchers suspect that the sleep is a symptom of the underlying cause, such as caffeine withdrawal or excessive stress.
Cause and effect
In many cases, oversleeping seems to be a symptom of an underlying condition that is itself producing health problems, such as depression, sleep apnea, or heart disease. But according to a literature review conducted sleep specialist and clinical psychologist Dr. Michael Grandner, oversleeping can cause direct health harm through several mechanisms: sleep fragmentation, increasing fatigue and lethargy, suppressing immune function, disrupting circadian cycles (through more time spent in darkness), and taking time away from mentally and physically stimulating activity.
In fact, controlled studies have found that when people are instructed to spend more time in bed — leading to longer sleep — they show increased fatigue, lethargy, fragmented sleep, irritability, depression, soreness and pain, inflammation, and lowered mood, reaction time, math performance.
If you are a regular over-sleeper, there are a few measures you can take to correct the problem. First, make sure you’re not caught in an undersleep-oversleep cycle: make sure you are getting enough sleep every night. If oversleeping on the weekends throws your sleep rhythms off, cut out that habit. Avoid behaviors that might make it hard to fall asleep at night, such as late naps or caffeine or looking at screens too close to bed time. Make sure you get plenty of exposure to bright sunlight as early in the day as possible.