Why Do Daytime Naps Increase Risk of Dying?
This is the question confounding most who have gotten wind of the study from the University of Cambridge. Most of us recall with fondness the daily naps we had as children and we lovingly look on as our family member snoozes cutely on the sofa.
But now all that fondness crinkles up in one fell swoop when we find daytime naps are not only not as healthy as we thought – they actually increase the risk of dying early.
The Cambridge researchers followed 16,374 men who participated in the European Prospective Investigation Into Cancer-Norfolk study. The participants were interviewed for nap frequency and were followed for 13 years by the researchers.
During that period, a total of 3,251 people died. The researchers then correlated these deaths with the participants’ napping habits, while removing other confounding elements – including age, gender, social class, education, marital and employment status, weight, exercise, smoking and alcohol, depression, general health, medication and drug intake, nighttime sleeping and other health conditions.
The researchers found those who napped less than an hour per day had a 14% increased risk of death, while those who napped for more than an hour had a 32% increased risk of death.
Napping increased the risk of death from respiratory diseases even more. Those who napped for less than an hour a day were 40% more likely to die early from a respiratory disease, while those napping more than an hour per day had better than twice the risk of early death from respiratory disease.
Not the first study showing napping linked to early death
This is not the first study that has shown daytime napping is not healthy. A study from Japan’s Niigata University Graduate School of Medical and Dental Sciences followed 67,129 Japanese men and women who were between 40 and 79 years old for 13-15 years. None had a history of strokes, heart disease or cancer.
This study found those who napped during the daytime were 19% more likely to die from any cause, 31% more likely to die from cardiovascular disease, and 26% more likely to die from other diseases.
These ratios were greater among those who did not work a steady job or were unemployed. They also increased among those in lower education levels.
The researchers concluded:
“Daytime napping is associated with elevated risk of CVD mortality as well as non-cardiovascular/non-cancer and external deaths. Daytime napping may elevate risk of CVD death through some biological effects but, to a larger extent, some comorbid disorders causing weight loss or associated with non-regular employment and low education level could explain this association.”
So why daytime nappers die earlier?
Before you throw your hands up in disgust: There is good reason for this. Other research has shown that heart disease and early mortality is also linked with too much sleep and too little sleep. Sleeping less than five hours or more than nine hours has been linked with these and other conditions.
In addition, further research has linked healthy REM-stage cycles with healthy sleep. REM means “rapid eye movement” because during this deep sleeping state, the eyes will flutter. In this stage, our bodies fall into their deepest sleep state, and it is in this stage that our cells and tissues detoxify and recharge the most.
A REM-stage cycle lasts about 90 minutes, and the REM part typically occurs in the last half of this cycle. After the REM stage, the person will cycle into a lighter sleep state before plunging back into another cycle.
As we pointed out in this article, a lack of REM-stage sleep has been linked to neurological disorders such as Parkinson’s disease and dementia. In one study, 139 Parkinson’s or dementia patients were tested for their REM-stage sleep health. It was found that a lack of consistent REM-stage sleep was associated with these conditions.
Other studies by French researchers had similar findings. Parkinson’s was linked to REM-stage sleep interruption and REM-stage disorders like REM-stage sleep interruptions, heavy movements during REM-stage sleep, and sleepiness due to a lack of REM-stage sleep. In one study, 50 Parkinson’s patients were video-monitored and 100 couples were interviewed. About 60 percent of the Parkinson’s patients had abnormal REM-sleep episodes.
Other research found REM-stage deficiency often precedes Parkinson’s and dementia by a number of years. Also, sleep apnea is more prevalent among those with Parkinson’s, and so is restless leg syndrome.
Sleep allows our central nervous system – which includes the brain cells – to detoxify and unwind. It allows the hippocampus and the rest of the limbic system to process memory storage, easing the burden of brain cells in the cortices. These functions are important because they reduce the stress on brain cells. Research has shown that the processes that take place during REM-stage sleep allow our brain cells to ‘reset.’ Oxidative stress, a common symptom of all types of dementia and Parkinson’s, is reduced during REM-stage sleep.
Sleep is critical for our body’s recovery. While we are sleeping our immune system kicks into high gear and detoxification processes increase. Reactive oxygen species – also called free radicals – are also cleared out of the system during sleep.
Much of this occurs during REM-stage sleep because in this condition we break free of our hold on our physiology. This allows the functioning of the immune system to speed up.
Also, our probiotic colonies are typically more active during REM-stage sleep.
One of the problems with naps is that they do not allow us to get to REM-stage. The cycle-down time is typically not long enough during a nap. And even if we got to REM-stage sleep, we would be jolted out of it in that hour or so nap-time.
And because naps are often taken in lieu of some of our nighttime sleep – when we get our REM-stage sleeping – the net result is a loss of total REM-stage sleep.
This was confirmed a study of 5,888 men and women from the University of Pittsburgh. Here the researchers found that daytime sleepiness – the result of a lack of REM-stage sleep and a reason to nap during the day – doubled the risk of dying from cardiovascular disease in women and increased it by 40% in men.
This entire relationship – REM-stage sleep and early death – was confirmed in an international multi-center study that tested 636 people – half of whom had a sleep disorder called idiopathic REM sleep behavior disorder. The researchers found that those with the REM-stage sleep disorder had over double the risk of having a heart attack, significantly more depression and depression medications than those without the disorder.
The bottom line is that we don’t just need sleep every night – as if sleep is just one long continuous thing. We need a certain amount of REM-stage sleep every night, and if we don’t get enough of it, there will be negative health consequences.
This means that having an afternoon nap in itself is not a problem. What is the problem is the lack of REM-stage sleep that occurred the night before. This is added to the fact that a person taking an afternoon nap will also be less likely to catch up on that REM-stage sleep loss the next night.
They will likely repeat the cycle again the next night and day.
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Tanabe N, Iso H, Seki N, Suzuki H, Yatsuya H, Toyoshima H, Tamakoshi A; JACC Study Group. Daytime napping and mortality, with a special reference to cardiovascular disease: the JACC study. Int J Epidemiol. 2010 Feb;39(1):233-43. doi: 10.1093/ije/dyp327.
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