Most of us aren’t big fans of the alarm. That’s because the alarm interrupts our natural sleep cycle. Not cool.
After all, adequate sleep is crucial for our energy, appearance, longevity, sex life – you name it. Sleep is when our cells (especially our brain cells) rid themselves of inflammatory garbage. Sleep is also when our body repairs itself with hormones like testosterone and growth hormone. And we need plenty of Zs to get those hormones really firing.
A lack of Zs, on the other hand, causes a host of undesirable effects: high cortisol, high blood sugar, low grade inflammation, reduced energy expenditure… the list goes on and on. Sleep deprivation is bad for your body. You knew that already.
But what about too much sleep? Is that harmful?
As someone who sleeps 9-10 hours per night, I’ve wondered about this for some time now. But I never really dug into the research. I’ll admit it: I was scared of what I might find out.
Recently though, I steeled my nerves and did dig into the research. You’ll be interested in what I found.
Before we get there, however, I need to lay some groundwork. This will help you draw your own conclusions later.
Across dozens of studies involving thousands of subjects, scientists have found that both extremes of sleep duration – too short and too long – are linked to increased risk of death, cardiovascular disease, stroke, and other bad outcomes. When you graph the data, it looks like a U. The lowest risk is in the middle. This is the sweet spot for sleep duration.
This low-risk sweet spot, according to a recent meta-analysis, is around 7 hours of sleep per night. When all the data was compiled, every hour below the sweet spot carried a 6% increased risk of death, while every hour above the sweet spot carried a 13% increased risk of death. The figures were similar for stroke and CVD.
On its face, this finding is fairly shocking. It means that, in terms of negative outcomes, 8-9 hours of sleep is twice as bad as 5-6 hours of sleep.
Really? I know how it feels to get 5 hours of sleep. It’s not enough. What gives?
Proposed reasons that long sleep kills you
I’ll skip the discussion of why short sleep increases risk of death. We already covered that. Instead I’ll go straight to how long sleep might kill you.
Let’s return to that meta-analysis because it seems to be the last word on this topic. In the paper, the authors give four reasons why long sleep could cause increased mortality risk. I’ll give my thoughts on each:
1) “Long sleep duration may be associated with an increased risk of atherosclerosis.” 82
First of all, the study cited to support the claim doesn’t actually support the claim at all. Just read the conclusion: “Longer measured sleep is associated with lower calcification incidence independent of examined potential mediators and confounders.” To my ear, “lower calcification” sounds like good news for long sleep.
But even if sleep duration and atherosclerosis were linked, this correlation wouldn’t prove that long sleep is harmful. More on that soon.
2) “Excessive time in bed has been linked to increased sleep fragmentation 89, which was considered to be associated with more severe arteriolosclerosis and subcortical macroscopic infarcts.”
There are two associations here: 1) the link between time in bed and sleep fragmentation and 2) the link between sleep fragmentation and heart issues.
Yet neither link gives us clues about the direction of causality. For instance, maybe sleep fragmentation has an underlying cause (say, sleep apnea) that makes one stay in bed longer. And maybe heart issues cause sleep fragmentation, not the other way around.
Here’s an example to drive the point home. Let’s assume that water consumption is directly linked to a person’s weight. Let’s also assume that a person’s weight is directly linked to their risk of heart disease. Based on these associations, can we say that drinking lots of water causes heart disease? The question nearly answers itself.
3) “Long sleep duration has been linked with feelings of fatigue and lethargy, which in turn would cause sleep extension. These states may fail to provide sufficient restoration against stress and disease and then lead to increased mortality.” 91
Again, this proves nothing against sleeping in. Fatigue and lethargy are common symptoms. They can be caused by sleep apnea, depression, heart problems, etc., etc.
A person with these underlying issues will stay in bed longer. That’s believable. What’s harder to believe is that long sleep causes any of those problems. There’s no evidence to support that claim.
4) “Long duration of sleep was associated with depressive symptoms, low socioeconomic status, unemployment, low household income, low level of education, and other risk factors for mortality and cardiovascular events.” 92
Association, association, association with no mechanism in sight – no mechanism to explain how long sleep might cause any of these problems. You know how I feel about this by now.
Will too much sleep kill you?
I’ve been building to this point for a while. I hope you’re still with me.
Let’s summarize. In a large population, both extremes of sleep duration are correlated with bad outcomes. In the case of sleep deprivation, this makes sense. Short sleep is proven to harm the body, so it’s not a stretch to say that short sleep causes an increased risk of death.
The case against long sleep, on the other hand, is merely correlational. The fact is: nobody can say how too much sleep harms the body. Rather, it appears that long sleep is less of a cause than a marker for poor health. The causes lie elsewhere.
Sleep apnea is likely one of these causes. Sleep apnea increases the risk of heart disease and increases sleep time. There’s one potential villain at least.
The authors of this 2010 study came to a similar conclusion:
“No studies published to date have demonstrated a possible mechanism mediating the effect of long duration of sleep as a cause of morbidity and mortality. […] Depressive symptoms, low socioeconomic status, unemployment, low level of physical activity, undiagnosed health conditions, poor general health, and cancer-related fatigue have all been shown to be associated with long duration of sleep and to confound the association with morbidity and mortality.”
Dream away, let the alarm take a holiday…
Lots of good stuff happens while we sleep. The body heals, the hormones flow, and the brain detoxifies. Does anything bad happen? Not that we know of.
So schedule-permitting, turn off that alarm and sleep as long as you like.