The first international review to compare night owls with early risers outlines the health risks associated with preferring late nights. However, these risks may not be set in stone.

A recent review takes a fresh look at the impact of being a night owl.

Most individuals fit one of two chronotypes: We are morning people or evening people.

Either we prefer to stay up late — and are referred to as night owls — or we rise earlier and go to bed earlier.

These patterns in circadian preferences are, to a certain extent, written in our genes.

Over the years, the medical community has debated the health impacts associated with each chronotype, and the findings have not always been conclusive.

To develop a clearer picture, a group of scientists from a number of institutions have conducted the most extensive review of relevant research to date. Their findings were published recently in the journal Advances in Nutrition.

Sleeping, eating, and health

The scientists were especially interested in understanding the relationship between circadian rhythms and eating patterns — called chrono-nutrition — and overall cardiometabolic health.

Because modern life is often hectic, eating and sleeping patterns may frequently be disturbed. Exposure to artificial light sources can also misalign our circadian patterns.

These disruptions can alter cyclical metabolic processes, such as glucose control, lipid metabolism, and blood pressure.

Scientists are working to determine the long-term health effects of these changes.

Because this area of study is in its infancy, the authors of the recent review delved into previous studies, hoping to identify patterns in results.

The team found that individuals who went to bed later tended to have less healthful eating patterns.

For instance, they generally ate later in the day, at less regular times, and they consumed more alcohol, sugar, and caffeinated products than earlier risers. Night owls were also more likely to skip breakfast.

In addition, night owls were likelier to consume fewer vegetables and grains. They also ate less often but had bigger meals.

This eating pattern may explain the finding that night owls had an increased risk of heart disease and metabolic conditions, such as type 2 diabetes.

In fact, one study showed that night owls were 2.5 times more likely to have type 2 diabetes than early risers.

The leader of the study, Suzana Almoosawi, Ph.D., a research fellow at Northumbria University in the United Kingdom, explains that "In adulthood, being an evening chronotype is associated with greater risk of heart disease and type 2 diabetes, and this may be potentially due to the poorer eating behaviour and diet of people with evening chronotype."

According to the researchers, being a night owl can even affect the way a person manages their diabetes: "Our review also found that people who have a poorer control of their diabetes are more likely to be evening types," says Almoosawi.

The body's circadian fluctuations in glucose metabolism may mediate the link with type 2 diabetes. Throughout the day, glucose levels decline, and by the evening they are at their lowest point.

However, because night owls eat later in the day, glucose levels spike just before bedtime. This goes against the body's regular biological processes, and so it could impact metabolism.

Growing knowledge but gaps remain

The review uncovered some other interesting findings. Perhaps unsurprisingly, children were much more likely to be early risers, including 90 per cent of 2-year-olds and 58 per cent of 6-year-olds.

As people enter old age, they are more likely to revert to their early-rising preferences of youth.

Although this type of study is still in the initial stages, and much more research is needed, the findings to date may have huge implications for public health.

"Scientific evidence is providing increasing insight into the relationship between your chronotype, diet, and cardiometabolic health."

Study co-author Leonidas G. Karagounis, Nestlé Health Science

Karagounis continues, "Further research on the best methods to assess an individual's chronotype and how this may affect their long-term cardiometabolic health can potentially guide the development of health promotion strategies aimed at preventing and treating chronic diseases based on an individual's chronotype."

The review also highlights gaps in our understanding. For instance, the existing body of literature does not provide much information about why our circadian rhythms and eating patterns shift throughout our lifespans.

Though scientists are still unsure why our preferences morph as we age, modern living may drive this pattern, at least in part.

As children, we are more likely to rise early, but as we become embedded in society, we are more likely to develop into night owls. In older age, as we pull back from society's cut and thrust, we tend to go back to rising early.

It will take far more research to determine whether this pendulum swing in chronotype results from social pressures — such as school and work start times — or whether it is triggered by hormonal changes, for example.

However, it seems that the adverse health effects of being a night owl may predominantly revolve around dietary habits that are, for the most part, modifiable.

For instance, by eating more healthfully, not skipping breakfast, and drinking less alcohol, a person may be able to avoid some of the risks.