It's a little hard to believe there's such a thing as sleeping too much, since so many of us feel like it's a struggle to even get barely enough.
But it's true: You can overdo it on sleep.
While it's tough to pinpoint the "just right" amount, most adults need between seven and nine hours a night to feel and function their best.
Regularly logging more than nine hours of sleep a night may be a sign of an underlying medical condition, but it also puts you at risk for a whole host of health concerns. Here are some of the biggest risks of catching too many Zzs.
Sleeping too much can raise depression risk.
In a 2014 study of adult twins, researchers found that long sleep duration increased a person's risk of depression symptoms. The study participants who slept between seven and nine hours a night had a 27 percent heritability of depressive symptoms, while those who slept nine hours or more had a 49 percent heritability.
It could impair the brain.
A 2012 study found that among elderly women, sleeping too much (or too little) worsened brain function over a six-year period. Women who slept more than nine hours each night (or fewer than five) displayed changes in their brains on par with aging two years, HuffPost reported at the time.
It might make it harder to get pregnant.
In 2013, a Korea research team analyzed the sleep habits of more than 650 women undergoing in vitro fertilization. They found that pregnancy rates were highest among the women who got seven to eight hours of sleep a night and lowest in women who got nine to 11 hours.
The findings, however, did not establish a clear causal relationship. "We know that sleep habits can certainly alter circadian rhythms, hormone secretions and menstrual cycles," Dr. Evan Rosenbluth, a reproductive endocrinologist, told HuffPost at the time. "[But] the effect on infertility is a little harder to tease out, because there are so many details that are hard to control for."
Sleeping too much can increase diabetes risk.
In a small study from Quebec, researchers found that people who slept more than eight hours a night were twice as likely to develop type 2 diabetes or impaired glucose tolerance over a six-year period than people who slept between seven and eight hours a night, even after controlling for differences in body mass.
It can lead to weight gain.
The same researchers also looked at body weight and fat gain among Quebec adults over a six-year period. They found that short and long sleepers gained more weight over the six years than people who slept seven to eight hours a night. People who slept nine to 10 hours each night were 25 percent more likely to have gained 5 kilogramsover the study period, even after controlling for food intake and physical activity. "Hence, these results emphasize the need to add sleep duration to the panel of determinants that contribute to weight gain and obesity," the authors wrote in the study.
It can hurt the heart.
In research presented at a 2012 American College of Cardiology meeting, sleeping eight or more hours each night was linked to an increased risk of heart problems. The researchers analyzed data from over 3,000 people and found that long sleepers had two times the risk of angina and 1.1-times the risk of coronary artery disease.
Sleeping too much may lead to an earlier death.
In a 2010 review of 16 different studies, researchers found an increased risk of dying -- of any cause -- among both short and long sleepers. Sleeping more than eight hours a night was associated with a 1.3-times greater risk of death among the 1,382,999 various study participants.
A previous version of this article appeared in February 2015.
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