A night owl or an evening person with a late sleep-wake cycle could be at a higher risk of cognitive decline with age compared to an early bird or a morning person, a study has found.

Chronotype refers to one’s sleep-wake type or times during the day when one naturally tends to be awake and asleep. A ‘night owl’ chronotype is said to have a later sleep-wake cycle, compared to an ‘early bird’ or a ‘lark’.

“Are you an early bird or a night owl? It’s hard to adjust what your biological clock your so-called chronotype is, but you can adjust your life to it as best you can,” study author Ana Wenzler, from the University Medical Center Groningen, the Netherlands, said.

Analysing the performance of about 23,800 participants on a cognitive test over a period of 10 years, the study found that evening people decline cognitively faster than morning people. The findings have been published in The Journal of Prevention of Alzheimer’s Disease.

“Unhealthy behaviour such as smoking, drinking and unhealthy eating happens more often in the evening,” Wenzler said.

“In our study, we also saw this: evening people smoke and drink more often and exercise less. Twenty-five per cent of the risk of cognitive decline can be explained from our research by smoking and poor sleep,” she said.

A greater decline was seen in higher-educated people a delay of an hour in the sleep-wake cycle corresponded to a decline of 0.8 in cognition per decade.

Wenzler said the decline might be related to their disturbed sleep rhythm.

“They are often people who have to go back to work early in the morning and are therefore more likely to sleep too short, giving their brains too little rest,” she said.

The author explained that people’s biological clock can change with age.

“Children are morning people. That changes when you reach puberty, when you become an evening person. Around your 20s, that gradually shifts back towards morning people for most people. By the age of 40, most people are morning people again,” Wenzler said.

However, this is certainly not the case for everyone, which is probably why evening people deviate from the norm, according to Wenzler, who recommended working against one’s body “as little as possible”.

“‘You can try to go to sleep earlier, but if your body is not yet producing melatonin (sleep hormone), it will not work: your body simply does not want to sleep yet,” she said.

Wenzler added, “If (not working against body) is not possible, your brain does not get enough rest, and you are more likely to adopt bad habits. It would be nice if more consideration was given to evening people who now have to work early: for example, by giving them the option of starting later.