Not being a morning person may come down to genes, study suggests

Whether you are a night owl or an early bird, don’t bother fighting the impulse because it’s probably in your genes, a study has suggested.

Scientists have long known that all plants and animals – from lowly phytoplankton to homo sapiens – have internal biological clocks attuned to a 24-hour cycle.

But within this so-called circadian rhythm, individuals of some species, including humans, may have a natural preference for day or night.

Previous research had singled out genes with an unspecified influence on these rhythms.

But very little was known about which parts of our genetic code were involved.

A research team led by David Hinds of California-based biotechnology company 23andMe trawled the genomes of 89,283 people for clues.

The team compared the findings with responses to a web survey in which the same individuals were asked to indicate whether they preferred mornings or evenings.

The study, published in Nature Communications, reported a link between more than a dozen gene variants and healthy individuals who said they were at their best in the morning.

Early risers were significantly less likely to have insomnia or need more than eight hours of sleep per night. They were also less prone to depression than the 56% of respondents who described themselves as night owls.

The researchers also found that after taking into account the effect of age and sex, morning people were likely to have lower – and thus generally more healthy – BMI, or body-mass index, a measure of the ratio between height and weight.

None of these correlations, the researchers cautioned, necessarily implied a cause-and-effect relationship.

Nor did the team find genetic links with sleep disorders such as insomnia, apnoea or sweating while asleep.

The mechanism controlling circadian rhythms is found in neurons located in a part of the brain called the suprachiasmatic nuclei, in the hypothalamus.

The same process is involved in jetlag, which is the feeling of being out of phase – either sleepy or wide awake – with a given time cycle.