Health issues for those who stay up late

Benjamin Franklin claimed that “early to bed and early to rise makes a man healthy, wealthy and wise”. Recent research suggests that the practice may actually good for health, but not necessarily for wealth accumulation or brain power.

Men who are night owls are more likely to have diabetes and female night owls are more than twice as likely to have metabolic syndrome as their early rising equivalents, according to a study published in the Journal of Clinical Endocrinology & Metabolism. The reasons for this effect are unclear, but the researchers suggested that consuming more calories after 8pm and exposure to artificial light at night can both affect metabolism.

Whether individuals are larks or owls is genetically determined and this sleep chronotype is also thought to affect fertility, pain threshold, cancer risk and personality traits. Preference for mornings or evenings is largely dictated by the period-3 gene; people with the long version of period-3 are larks, while those with the short version are owls.

Larks always eat breakfast within an hour of waking, according to Loughborough’s Sleep Research Centre, and this is a good indicator of whether an individual is a morning or evening type. But owls tend to eat more in the evening and this can lead to weight gain. Evening meals may not feel as filling as food eaten during the day because of lower levels of the satiety hormone leptin.

Other studies have shown that owls are more likely to snore and suffer from sleep apnoea, possibly because they are more overweight, and that they have poorer memories. Because owls tend to go to bed later, their sleep ends prematurely and often don’t have their last phase of dreaming sleep, which helps the brain lay down memories. Owls tend to be more sensation-seeking, risk-taking and outgoing, but are more prone to depression, possibly because of a lack of sleep.

In relation to the other aspects of Franklin’s maxim, an older study published in the BMJ concluded that larks were not richer or cleverer than owls. In fact, the study found that owls had a greater income and were more likely to have access to a car than others. But this study found no clear link to health problems. It did however conclude that sleeping for more than eight hours a night was associated with increased mortality, but that it mattered little whether the sleep was taken in the early or late part of the night.