People who describe themselves as an “evening person” may be at higher risk of poor health compared to morning types.
The new study followed over 430,000 adults in the United Kingdom between the ages 38 to 73 for six and a half years. At the end of this period, the researchers compared the mortality rates of the morning and evening types of people.
The data was taken from the U.K. Biobank -- a large pool of data designed to identify risk factors of major diseases -- and published in the Chronobiology International journal.
The researchers think the association between sleeping late and ill health may be related to our internal body clock being misaligned to social activities such as working and eating, or the effects of “social jet lag” -- forcing yourself to have a different sleeping pattern on weekends compared to workdays.
But at this stage it is worth remembering that the finding is only an association, not a cause-and-effect relationship. The study took into account a number of factors which might have affected the results, such as age, gender, smoking and obesity. But there's a chance another factor is at play which the researchers might’ve missed.
For instance, stress, diet, isolation and drug and alcohol use are all known to contribute to ill-health and may be responsible for the different medical outcomes for morning and evening types.
It is thought that chronotype -- the medical term used to describe our preferences for morning or evening -- are around 20-50 percent determined by our genes. This means that we could have some control over our preferences.
They’re investigating whether bright light therapy in the morning, or melatonin in the evening, might be able to shift our chronotype, possibly improving health outcomes.
The authors of the study also suggest that more thought should be given to how our working patterns are designed.
“These findings suggest the need for researching interventions aimed at allowing evening types greater working flexibility,” the researchers said.
“The switch to daylight saving time is perceived as more uncomfortable by evening types than morning types,” the study said, “placing a further burden on individuals who are already struggling with when to start the working day."
George Gillett is a resident affiliated with the University of Oxford working in the ABC News Medical Unit.