Morning grumpiness has long been attributed to a lack of coffee, but new research has cast doubt on whether a caffeine fix can lighten your mood.

Findings published in the Nature Communications scientific journal attribute the grumpiness that sets in when desperately reaching for the snooze button on the alarm clock to our genes.

Many of us class ourselves as morning people or night owls and the study's authors have found genetic variations near genes known to regulate the body clock and control light-sensing.

Not surprisingly, morning people are classed as those who choose to rise and rest early, those who are at their best in the evenings choose a later routine.


This whole routine revolves around a circadian rythym, which follows a 24-hour cycle.

This rythym also affects natural processes, including a person's preference for the morning or evening.

"Several genes whose products regulate circadian rhythm are already known, but it was previously unclear whether these were linked to personal preference for the morning," says a summary of the "genome-wide study".

It was led by David Hinds and he and his colleagues studied 89,283 people.

"The individuals reported a preference for the morning or the evening in a web survey.

"The authors identify specific genetic variations associated with healthy individuals' preference for the morning, and show that some of the identified genetic variations are located near genes that are known to regulate circadian rhythm," the summary says.

"They also find genetic variations near genes that control light-sensing and show that they are associated with preference for the morning."

The study also found people with sleep disorders and higher body mass indexes would often report a preference to the morning, although no evidence for a "causal relationship" was found, the authors say.

They say their work will help future research into Circadian rhythms and sleep disorders.