Getting anywhere between six to nine hours sleep is ideal for your heart, but any more or less could potentially boost your risk of cardiovascular afflictions, including coronary heart disease or a stroke. At least, that’s according to a new study – led by the Onassis cardiac surgery center in Athens – presented at the European Society of Cardiology Congress in Munich this week.
Around 17.7 million people die each year from cardiovascular diseases, primarily heart attacks and strokes – that’s 31 percent of all deaths, by the way. Smoking, unhealthy diets, physical inactivity, and a high salt intake are all linked to increased likelihood of these problems. A lack of sleep has been thought to be a factor too, although it’s been uncertain how big a factor it might be.
This new study sounds like an easy fix then: get more sleep on a regular basis and lower your risk. There are, as ever, some caveats – not least that the study isn’t available to read yet.
So what's the story? Well, the good news is that it's a meta-analysis, a study that reviews data from many pre-existing studies in an attempt to find correlations or trends. In this case, the data involved a million adults spread across 11 studies.
According to the abstract, it appears that those that got fewer than six hours per night had an 11 percent increased risk of getting a heart condition over the following nine years, compared to those that got those requisite hours of sleep. Those that slept for more than nine hours had a 32 percent increased risk over the next nine years.
No cause-and-effect relationship between sleep and heart health is given here. Sleep is known to have an influence on metabolism, blood pressure, and inflammation, but specific links between sleep and heart health are somewhat elusive.
More importantly, however, this talks about relative risk. Absolute risk is your current, actual risk: for example, let’s say you have a 10 percent risk of sneezing today. That means today, you’ll have a one-in-ten chance of sneezing.
Relative risk is all about the change in absolute risk: for example, if you tickle your nose, you have an increased risk of, say, 20 percent at sneezing. That means, from a one-in-10 chance (10 percent) pre-tickling, your tickled nose now has a one-in-8.3 (12 percent).
The point is that relative risks can sound scary, but it all depends on the original absolute risk. If the absolute risk itself isn’t that high, then a sizable relative risk might not mean much anyway.
For this new study, the absolute risks aren’t given in the abstract. So without knowing how likely people that sleep between six to nine hours per night are to get cardiovascular disease in the next nine years, all we have are the relative risks.
Saying that, sleeping properly clearly has its benefits.
Per the Centers for Disease Control and Prevention (CDC), a lack of sleep is linked to an increased risk of type 2 diabetes, obesity, depression and, yes, heart disease. Again, plenty of research is trying to work out how much of a factor a lack of sleep is, but suffice to say regular bouts of sufficient sleep is vital to good mental and physical health.
Emily McGrath, senior cardiac nurse at the British Heart Foundation, told the Associated Press that “this research needn’t trigger alarm bells for those of us partial to a sleepless night or a weekend lie-in. However, if you regularly struggle with your sleep, it’s an important reminder to speak to your GP.”
The problem is that it’s not so easy getting the right about of sleep. One major problem is the enduring 9-to-5 work period: Based on a century-old mantra with no scientific basis, it means that only people with the right sleep cycle fit this schedule. Night owls and early birds, who can’t change their chronotype, suffer needlessly as a consequence.