Scientists have assessed the relationship between sleep patterns and the ability to work until retirement

People with an evening chronotype, who are commonly referred to as "owls", are more likely to retire due to disability before reaching the usual retirement age than "larks". This conclusion was made by researchers who followed 5,679 Finnish residents for 12 years. The risk of assigning such a pension to participants with an evening chronotype turned out to be about 1.7 times higher. How biological rhythms can be related to health and working life expectancy — in the material of Izvestia.

How "owls" and "larks" were defined

The results are published in the journal Occupational & Environmental Medicine. The authors used data from the North Finnish Birth Cohort of 1966, a long—term population-based study that initially covered 96% of children born in two northern provinces of the country.

The chronotype reflects the body's natural circadian rhythm: when it's easier for a person to wake up, at what time they feel more alert, and when they prefer to work. Morning, intermediate, and evening types are usually distinguished.

In 2012, when the participants turned 46, they answered questions about their regime and well-being. The researchers were interested in how easily a person wakes up in the morning, how he feels in the first half hour after waking up, at what time he prefers to work and whether he considers himself to be an "owl" or a "lark".

The initial sample included 2,597 men and 3,082 women. The evening chronotype was determined in 253 men and 381 women — 9.7% and 12.4%, respectively. 1,182 men and 1,355 women had the morning type. The rest were assigned to the intermediate group.

The responses were then compared with information from Finland's national employment and pension registers. This made it possible to track who was awarded a disability pension for the first time in the next 12 years.

How different was the risk

During the observation period, 135 men and 249 women received such a pension — 5.2% and 8.1% of the total number of participants of the corresponding gender. These indicators apply to the entire sample, not just to the "owls". People who were assigned to the evening chronotype at the age of 46 had about a 1.7-fold higher risk of receiving a disability pension over the next 12 years than those with the morning type. The connection was found in both men and women.

It persisted after taking into account socio-economic factors, including the level of education and the nature of the profession. Therefore, the difference could not be explained solely by the fact that representatives of different chronotypes were engaged in different jobs or had different education.

A 70% increase in risk does not mean that 70% of the "owls" have received a pension. This is a relative comparison with "larks", which in itself does not show the absolute probability for a particular person.

Why it is important to clarify the reason for retirement

The researchers studied the assignment of a disability pension. As specified, in Finland, such a payment is provided after severe and prolonged deterioration of health. Therefore, the result primarily concerns the preservation of the ability to work.

The authors suggest that a less favorable state of health in some people with evening chronotype may explain the increased frequency of such pensions. According to their estimates, by the age of over 50, the accumulated problems of some participants could already significantly limit their ability to work.

However, the evening chronotype in itself is not a diagnosis. The study does not allow us to say that anyone who prefers to stay up late and get up will necessarily encounter an illness or stop working earlier.

What role can sleep and lifestyle play?

One of the possible explanations proposed by the authors is a combination of less favorable habits and disorders of internal biological rhythms that can lead to sleep problems. But these are supposed mechanisms: the observed relationship does not prove that they led to the appointment of a pension.

At the same time, the chronotype has a pronounced genetic component. The authors used genetic information, which also confirmed its biological basis. The BMJ report notes that the chronotype is relatively stable in adulthood.

This is important for interpreting the results: belonging to the "owls" cannot be reduced solely to the habit of staying up late. The study examines the natural differences in circadian rhythms, which can be combined with the characteristics of sleep, health and working conditions.

What is known about recovery after work

Other scientific groups are also studying the relationship of the evening chronotype with work life. A separate study reported by the University of Eastern Finland in August involved 2,266 people of working age.

The somnologist explained the influence of standard schedules on the lives of larks and owls

People with evening chronotype were more likely to have difficulties recovering from work and balancing their professional and personal lives. Symptoms and diagnoses related to mental health were also more common, especially among participants with a pronounced evening type.

The authors found that the association of the evening chronotype with anxiety disorders could be associated with insufficient recovery after work and difficulties combining work with other areas of life. These data complement the context of the new study, but do not directly explain the cases of pension assignment: we are talking about a different sample and other indicators.

What the study does not prove

The strengths of the new job are long—term observation, a large sample, and the participation of people from different professional and economic groups. At the same time, the study remains observational and does not establish a cause-and-effect relationship.

Over the past 12 years, the health, working conditions, and life circumstances of the participants may have changed. Not all such changes could be taken into account in the analysis. Therefore, it cannot be concluded that the evening chronotype was the direct cause of disability.

The results raise the question of how to take into account individual biological rhythms while maintaining workers' health and ability to work. However, the work did not check whether changing the schedule or sleep pattern reduces the likelihood of receiving a disability pension. Separate studies are needed to evaluate such measures.