Six to eight hours a day

No "Free for ALL Friday" this week; it will be back next week.

We’re in low power mode for a few days due to spring break and Easter (which I’m aware was yesterday, but we are still recovering). Thanks for reading!

Getting enough sleep is one of the easiest things you can do to boost your memory, improve your mood, and positively affect many other parts of your life. It’s truly a magic elixir.

But science suggests you can get too much of a good thing. Because a massive study of 116,632 people’s sleep habits shows an unmistakable link between getting too much sleep, and dying prematurely.

Writing in the European Heart Journal, Chuangshi Wang of McMaster University in Canada examined the associations between people’s (a) total sleep time and frequency of afternoon naps and (b) total deaths and major cardiovascular events.

The findings:

• People who slept between eight to nine hours each night had a roughly 5 percent greater risk of developing cardiovascular disease or dying early, compared to people who slept only six hours per night.

• People who slept between nine and 10 hours per night had a 17 percent greater risk of the same conditions or early death than the six-hour-per-night sleepers.

• Those who slept more than 10 hours a night had a stunning 41 percent higher rate of cardiovascular disease or dying early.

There are three big caveats to note here. The first is our old friend, correlation versus causation.

Specifically, this study suggests that people who sleep longer are more likely to die early — but it doesn’t necessarily suggest that they die earlier because they sleep more.

It’s possible for example that people who develop cardiovascular disease are simply heavier sleepers and are more likely to die early. One doesn’t have to cause the other. Similarly, it might make sense that people who had nascent or developing health issues would be more likely to take daytime naps.

Second, and this will allow many of us to breathe a sigh of relief, the link between daytime napping and increased rate of death only mattered in people who were sleeping more than six hours a night.

So if you’re like me, and you struggle to get enough sleep at night with all your commitments but occasionally crash for an hour during the day, you’re good.

Finally, it should also be noted that in general, a median of 7.8 years passed between the first measurement of people’s sleep, and the follow up report that noted whether they were healthy, or had developed diseases or even passed away.

Based on that, it doesn’t seem that this turned out to be a study of mostly people who were sick to begin with, for example. In fact, the researchers said they controlled for age, BMI, smoking and alcohol use, and lots of other health and behavioral data.

Across the board, of the just over 116,000 people studied, 4,381 were deceased by the end of the study, and 4,365 had major cardiovascular events. So just over 7.5 percent combined.

The takeaways? Well, the good news is that this should ultimately make our sleep targets more reasonable, especially for busy entrepreneurs and other people.

“Get enough sleep — that is, six to eight hours a day,” Wang told the New York Times when it reported on this. “But if you sleep more than nine hours a day, you may want to visit a doctor to check your overall health.”

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Thanks for reading! Photo by Sinitta Leunen on Unsplash. I wrote about some of this before at Inc.com. During low power mode we usually skip the 7 other things section. It'll be back next week!