How Regularity Of Sleep Can Be Even More Important Than Duration

A recent, large (n=72,269) 8-year prospective* observational study of adults aged 40-79 has found an association between irregular sleep and major cardiovascular events.

*this means they started the study at a given point, and measured what happened for the next eight years—as opposed to a retrospective study, which would look at what had happened during the previous 8 years.

As to what qualifies as major cardiovascular events, they counted:

• Heart attack
• Cardiac arrest
• Stroke
• Cardiovascular death (any)

Irregular sleep, meanwhile, was defined per a bell curve of participants. Based on a sleep regularity index (SRI) score, those with a score of 87 or more were on the “regular” side of the curve, and those with a score of 72 or lower were on the “irregular” side of the curve.

What they found is that irregular sleep is associated with major cardiovascular events, regardless of the actual amount of sleep that people got. So in other words, you could be sleeping 9 hours per day, but if it’s a different 9 hours each day, your cardiovascular risk will still be higher.

How much higher?

• For those in the middle of the curve (so, moderate irregularity), it was 8% higher than those on the “regular” side.
• For those on the “irregular” side of the curve, it was 26% higher than those on the “regular” side.

All of the above is after taking into account confounding variables such as age, physical activity levels, discretionary screen time, fruit, vegetable, and coffee intake, alcohol consumption, smoking, mental health issues, medication use, and shift work. Which is quite something, given that shift work is a very common reason for irregular sleep schedules in a lot of people.

Limitations

While, as noted above, they did their best to account for a lot of things, this was an observational study, not an interventional study or a randomized controlled trial, and as such, it cannot truly establish cause and effect.

For example, an observational study in the 90s found that the sport most strongly associated with longevity was polo. For any unfamiliar, it’s a game played on horseback with mallets and balls. Why was this game so much better than, say, swimming? And the answer is most likely that polo is played almost entirely by very rich people. It wasn’t the sport that enhanced longevity—it was the wealth.

So similarly here, it could be for example that people who are predisposed to heart conditions, are prone to having irregular schedules. We won’t know for sure until we have interventional studies (and we probably can’t get RCTs for this, for practical reasons).

Still, it seems likely that the association is indeed causal, in which case, having a regular sleep schedule if at all possible seems like a very good way to look after one’s health.

You can read more about the study here:

Irregular sleep may elevate risk of major cardiovascular events

Practical take-away

This study strongly suggests that sleep regularity is even more important than sleep duration.

This means that there is extra reason to not sleep in past one’s normal getting-up time, even if one had a less restful night.

That’s the end of sleep that’s the most important in practical terms, too, because we can control our getting-up time, whereas we can’t really control our going-to-sleep time, because it’s perfectly possible to just lie there awake.

So, controlling the getting-up time is really the key to the whole thing. See also:

Calculate (And Enjoy) The Perfect Night’s Sleep

And for scope, you might enjoy reading:

Morning Larks vs Night Owls: How Much Can We Control Our Sleep Schedule?

Enjoy!