A large study covering 37 years from start to finish has revealed something about those who tend to stay up late: These night owls are more likely to die at a younger age, but due to smoking and drinking-related causes rather than how late they go to bed.
Data on 22,976 Finnish adult twins were analyzed for the study, with 42.9 percent identifying as "somewhat evening types" or "evening types". Technically, this is our chronotype – our tendency to want to sleep or be active at certain times.
Previous studies have suggested night owls have a higher mortality risk and a tendency to prefer riskier behavior. In this study, it seems a greater chance of an earlier death isn't directly due to chronotype but to what it leads to.
"Our findings suggest that there is little or no independent contribution of chronotype to mortality," says Christer Hublin, a researcher at the Finnish Institute of Occupational Health.
Instead, "the increased risk of mortality associated with being a clearly 'evening' person appears to be mainly accounted for by a larger consumption of tobacco and alcohol. This is compared to those who are clearly 'morning' persons."
Having identified the chronotypes for the study participants in 1981, the researchers followed up in 2018, looking at death rates ascertained through nationwide registers. Factors such as education, BMI, and sleep habits were adjusted for in the analysis, as well as the amount of smoking and drinking each individual did.
By 2018, the researchers found that 8,728 of the participants had died. The chance of dying from any cause was 9 percent higher in those who declared themselves definite (not "somewhat") evening types than those who were definite morning types.
However, non-smokers who also didn't drink much in this night owl group were at no increased risk of dying from any cause. The team found that smoking and drinking (leading to alcohol-related diseases as well as alcohol poisoning) were responsible for the extra deaths.
While being an evening person doesn't necessarily mean poor sleep habits, the two often go together. Impaired sleep can lead to a host of mental and physical issues and has also previously been linked to addictions – to nicotine or alcohol, for example.
"There is a reciprocal relationship between the reward system and circadian system, and the level of alcohol and substance use correlates with the preference to stay up later at night," write the researchers in their published paper.
Unlike the earlier study that prompted this one, the team didn't find any increase in cardiovascular-related mortality risk. There are some differences in the population sample though used – the previous research involved UK adults who were generally healthier than the average UK population, while here, the cohort's health was more in line with the general population.
As always, more detailed studies involving more people across more countries will help shed more light on this relationship further. However, it seems that we need to look not just at our sleeping habits but also some of the lifestyle choices that are more likely to happen due to those sleeping habits.
"Given the associations of chronotype with lifestyle factors that are known to increase the risk of premature morbidity and mortality, the independent contribution of chronotype to mortality is of relevance when providing public health recommendations related to sleep and chronotype," write the researchers.
The research has been published in Chronobiology International.