Sleeping <6 hours daily can up heart attack risk
People with a sleep duration of <6 hours/night have an increased risk of myocardial infarction (MI) than those who slept 6–9 hours/night, with additional data from Mendelian randomization analysis supporting a causal link between sleep duration and MI, a new study has shown.
While the association between short sleep duration and cardiovascular disease (CVD) risk has been shown in previous observational studies, these studies are prone to reverse causality and various confounding factors.
What is new in the current study is the establishment of a causal relationship between short sleep duration and MI risk using Mendelian randomization analysis. In the genetic epidemiology approach, genetic variants known to be associated with longer or shorter sleep duration were used as proxies for an individual’s lifetime exposure to sleep duration. Since randomization to a certain set of genes occurs since conception, this virtually eliminates environmental confounders and reverse causality — thus putting to bed the notion that short sleep duration can cause CVD.
The low-down on sleep hours and MI risk
In the prospective cohort analysis of 461,347 CVD-free participants, 5,218 incident MIs occurred over a median follow-up of 7 years. [J Am Coll Cardiol 2019;74:1304-1314]
Individuals who reported sleeping <6 hours/night (short sleepers) were 20 percent more likely to develop MI than healthy sleepers (6–9 hours/night; adjusted hazard ratio [HR], 1.20; p=0.001). Longer sleep duration of >9 hours/night was also associated with a 34 percent increased risk of incident MI compared with healthy sleep duration (HR, 1,34; p=0.0006).
Among those with short sleep duration, having frequent insomnia (HR, 1.30, 95 percent confidence interval [CI], 1.15–1.47) or difficulty rising from bed (HR, 1.81, 95 percent CI, 1.42–2.31) further exacerbated their risk for MI.
In particular, having high genetic risk* for coronary artery disease (CAD) exacerbated the risk of developing MI among short sleepers by 130 percent compared with healthy sleepers with low genetic risk (HR, 2.30, 95 percent CI, 1.88–2.82).
However, for these individuals with high genetic risk for CAD, having a favourable sleep duration was associated with cardioprotective effects in terms of MI risk (HR, 0.82; p=0.048). “Healthy sleep duration mitigated MI risk even among individuals with high genetic liability,” said the researchers.
Consistent with the findings from the prospective observational cohort, Mendelian randomization analysis also showed that short sleep duration (<7 hours) increased the risk of MI by 19 percent (odds ratio [OR], 1.19; p=0.0004).
Each additional hour of sleep reduced the risk of MI by 20 percent among those with insufficient sleep (OR, 0.80; p=0.013). Similar results were also seen in the risk of CAD (OR, 0.79; p=0.003).
“Altogether, our results highlight sleep as a modifiable and potentially causal risk factor for MI regardless of inherited risk and other sleep traits,” said the researchers.
Sleep a modifiable CV risk factor?
“[The causal link shown in Mendelian randomization analysis] is a most important result for the entire preventive cardiology community, as it finally confirms and corroborates the hypothesis already inferred by other (observational) studies of a causal relationship between sleep duration and risk of MI,” wrote the editorialists led by Dr Nicola Montano from the University of Milan, Milan, Italy. [J Am Coll Cardiol 2019;74:1315-1316]
“An additional interesting finding was that favourable sleep (between 6 and 9 hours) was able to reduce the negative effects of genetic liability, again supporting the view that behavioural factors, such as sleep, may interact with the genotype modifying the personal risk profile,” they continued.
“Finally, we think we have enough evidence to answer positively [that sleep is a potentially modifiable CV risk factor], and we can now focus all of our efforts on performing randomized controlled trials to test whether an increase in sleep duration may change the CV risk profile of short sleepers,” proclaimed Montano and co-authors.