"For example, for many years we thought drinking coffee was linked to heart disease, so there was some advice to patients not to drink as much coffee, but we found over time that people who drank more coffee were also more likely to smoke and have other unhealthy habits, so that was actually causing the heart risk," said Dr. Daniel Jones, past president of the American Heart Association and vice chancellor for health affairs and dean of the University of Mississippi School of Medicine.
For this reason, Jones said it would be premature for doctors to make recommendations to patients about altering their bedtimes rather than their sleep duration, which has been shown to affect cardiovascular health in multiple studies.
"The author of the study encourages people to go to bed earlier, but I think most scientists will look at this and say it's premature advice," Jones said.
However, Jones explained that although the study does not prove a late bedtime causes the heart risk, this finding may still make biological sense.
"There are a lot of potential reasons for this causal link, [such as] some of the chemicals or hormones in our body that are tied to sleep," Jones said. "People with less deep sleep and less duration of sleep have more adrenaline release, and it's likely that some of those hormones or chemicals could be related to the poor health of those with less healthy sleep habits."
According to Dr. Virend Somers, consultant in cardiovascular diseases and professor of medicine at the Mayo Clinic in Rochester, Minn., another possible explanation for the link between later bedtimes and cardiovascular risk could be that people who hit the hay after midnight actually clock less sleep than they think.
"Maybe when you go to sleep after midnight your sleep duration is shorter than you think it is," Somers said. "In other words, if I went to sleep at midnight and got up at 8 a.m., but my wife and kids got up at 6 a.m. to go to school, I might think that I slept a full eight hours, but I actually woke up several times when the house was noisy at 6 a.m."
Whatever the explanation may be, it remains well-established that a good night's sleep is an extremely important factor in leading an overall healthy lifestyle.
"People who sleep less seem to have poorer health in general and people who sleep more tend to have better health in general and that includes heart disease," Jones said.