It’s not the late nights, but the smoking and drinking that happen during those late nights, that are killing people who are “night owls” earlier in life, a new study claims.

Researchers studied twins in Finland for 37 years, looking at different chronotypes, the body’s natural inclination to sleep at a certain time.

Although they saw that the evening types had a slightly increased risk of dying than the morning types, it was those other habits that were at the root of that greater likelihood of premature death, the study found. The findings were published June 15 in the journal Chronobiology International.

“Our findings suggest that there is little or no independent contribution of chronotype to mortality,” said study author Dr. Christer Hublin, from the Finnish Institute of Occupational Health in Helsinki.

“In addition, 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,” Hublin said in a journal news release. “This is compared to those who are clearly ‘morning’ persons.”

Researchers were inspired to do this study by past studies that had linked night owls to a higher risk of disease, including heart problems.

Among those were data from the UK Biobank published as part of a 2018 study that found a small increased risk of death from any cause including disease, and from heart conditions, in evening types.

To understand what was happening, Hublin and Dr. Jaakko Kaprio, from the Finnish Twin Cohort study at the University of Helsinki, followed nearly 23,000 men and women, all twins and aged 24.

The participants were asked to declare themselves a morning or evening person clearly or to some extent.

Nearly 7,600 people identified as evening types “to some extent” and more than 2,200 as “definite” evening types. More than 6,300 were morning types to some extent and more than 6,700 were definite morning types.

The authors also considered participants’ education, daily alcohol consumption, smoking status and quantity, BMI and sleep duration.

Researchers then followed the participants up to 37 years later, to see if any had died. The study found that night owls were younger, drank/smoked more and they were less likely to report getting eight hours of sleep.

More than 8,700 of the total participants had died by 2018. The chance of dying from any cause was 9% higher among definite night owls compared to early birds.

Smoking and alcohol largely caused these deaths, not chronotype, the researchers noted. Nonsmokers were at no increased risk of dying. Alcohol deaths were from related disease and accidental alcohol poisoning.

More information

The Sleep Foundation has more on chronotypes for sleep.

SOURCE: Chronobiology International, news release, June 16, 2023