When it comes to sleep duration, we tend to worry about how little sleep we are getting without putting any thought into the consequences of getting too much sleep. In fact, I’m sure that many insomnia sufferers would argue that there is no such thing as too much sleep! Unfortunately, that theory is wrong — and studies are demonstrating that excessive sleep duration is linked to a number of negative health outcomes.
It’s thought that as many as 38 percent of Americans sleep for more than nine hours at night — and this can be just as bad (if not more so) for your health as living with chronic sleep deprivation. Since many insomniacs dwell on negative sleep thoughts, and have incorrect thoughts, behaviors, and ideas about sleep, being aware that long sleep duration is linked to negative health outcomes can actually be helpful.
A 2017 clinical review published in Sleep Medicine Reviews collected data from over five million participants from 137 studies to examine the relationship between long sleep duration and negative health outcomes such as:
- Heart disease
- High blood pressure
Defining normal sleep and long sleep
The definition of normal sleep and long sleep varied in each study, but normal sleep was typically around seven hours each night while long sleep was considered to be around nine hours or more of sleep each night.
The association between long sleep and health problems
The primary analysis found that, compared with normal sleep duration, long sleep duration was association with a statistically significant increase in:
- All-cause mortality
- Heart disease
Long sleep duration was not associated with an increased risk of high blood pressure and researchers were unable to determine any increase in risk for depression or high cholesterol.
The influence of age and gender
The review found that long sleep duration among those over 65 years was associated with a significant increase in the incidence of heart disease but there was no such increase in incidence among those under 65 years. With that being said, long sleep duration among those under 65 years was associated with a significant risk in incident obesity (a risk that did not exist among those over 65 years).
Although long sleep duration was associated with a significant increase in mortality, incident diabetes, heart disease, and stroke for both men and women, researchers found that long sleep duration was associated with a significant increase in incident obesity only among women.
Specific sleep duration and health risks
When looking at specific sleep durations, researchers found that long sleep duration of more than eight hours was associated with a significant increase in mortality, stroke, and coronary heart disease. Long sleep duration of more than nine hours was associated with an increase in incident cardiovascular disease.
After further analyzing data, the review found that longer sleep duration was linearly associated with increased mortality risk. In other words, as sleep duration increased, the association with risk of death increased, too.
Why is long sleep bad for your health?
It’s important to note that although this review showed that long sleep duration is a risk factor for negative health outcomes, it did not demonstrate that long sleep durations cause negative health outcomes.
With that being said, a 2007 study identified seven reasons why long sleep may be bad for your health:
Fragmented sleep is associated with negative health outcomes and may be caused by long sleep or excessive amounts of time spent in bed.
Fatigue and lethargy is associated with excessive sleep duration and these conditions may decrease resistance to stress and disease.
Immune function may be impaired by excessive sleep due to changes in cytokine levels.
Photoperiodic abnormalities (exposure to excessive periods of darkness) can confuse the body’s circadian rhythm and lead to health issues such as depression and seasonal affective disorder.
Lack of challenge/stimulation — spending too much time in bed means less time for exercise, a reduced sense of life purpose, and a lack of social interaction (all factors that are bad for overall health).
Depression may lead to the desire to spend more time in bed and depression is associated with a number of health issues such as heart disease.
Underlying diseases may be behind long sleep durations; specifically sleep apnea (which is associated with depression, high blood pressure, carotid artery disease, and kidney-disease); heart disease; and poor overall health.
This review should serve as a reminder that sleep quality is far more important than sleep quantity since both short sleepers and long sleepers are more likely to complain of poor sleep quality (and experience more health issues) compared to normal sleepers. It also demonstrates that more research is needed on the negative health implications of excessive sleep.
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Martin is the creator of Insomnia Land’s free insomnia sleep training. His online course uses CBT techniques to teach participants how to sleep better without relying on sleeping pills. More than 5,000 insomniacs have completed his course and 97 percent of graduates say they would recommend it to a friend.