Women are at their best in the morning and are better than men at coping with shift work because their body clocks are set differently, according to new research.
They are more resilient to disruptions in circadian rhythms – making them less susceptible to jet lag.
Women also tend to be most active earlier in the day – similar to patterns seen in children.
The phenomenon may be linked to their maternal instincts, explained co authors Dr Sean Anderson and Dr Garret FitzGerald from Pennsylvania University.
Women also tend to be most active earlier in the day – similar to patterns seen in children. Researchers suggest this phenomenon may be linked to their maternal instincts
Dr Anderson said: ‘One possible reason for the resilience to circadian disruption in females relates to their biological imperative.
‘Resistance to the negative consequences of circadian disruption coupled with improved sleep, even when experiencing nocturnal disturbances, may facilitate their adaptation to frequent nocturnal awakenings over a sustained period, given their predominant role in nurturing offspring.’
If you are a morning lark or a night owl depends on your genetic ‘chronotype’ – the propensity to sleep at a certain time of day. Women are more likely to be the former.
The Pennsylvania University team said a study of more than 53,000 people found age and sex ‘substantially affect’ body clocks.
Dr Anderson said: ‘Whereas children are typically morning types regardless of sex, after puberty males tend to be more evening oriented than females.’
Writing in the journal Science, the psychologists say that it mirrors previous findings in animal models.
Experiments on hamsters placed in constant darkness found females ran for shorter periods – indicating their molecular clock machinery oscillates faster.
They also showed significantly earlier onset of activity. It was reported female mice display greater fluctuations in behavioural rhythms during a 24-hour cycle – and peaked earlier in the day.
Women cope better with shift work because their body clocks are set differently to men, according to the research
The same was observed in a study of 91,105 Britons taking part in the UK Biobank health project.
Dr Anderson said: ‘This can be due to increased activity at night or decreased activity in the daytime, reflecting the conservation of more robust oscillations in activity rhythms among females.
‘Females also spend more time asleep, spend more of their time in slow-wave (deep) sleep, and are more resilient to nocturnal disturbances than males.’
Women are half as likely as men to sleep in the afternoon
Men are twice as likely to take an afternoon nap as women.
A poll of 2,000 Britons – half men and half women – found 13 per cent of men had a daily nap but just six per cent of women.
The study, by sofa and carpet specialist ScS, also found a quarter of women said they had never had a nap in their lives, compared with 16 per cent of men.
Lisa Artis, a Sleep Council adviser, said: ‘A power nap of 20 to 30 minutes is sufficient to turn off the nervous system and recharge the whole body and improve alertness.
‘Any longer is enough to put you in a deep sleep and leave you feeling groggy when you wake.’
Hormonal changes triggered by the menopause also add extra complexity to the ageing process for women.
Circadian rhythms are influenced by sex – and this interaction is remoulded throughout life, said the researchers.
Dr Anderson said: ‘Chronotypes converge during middle age as both sexes become more morning oriented.’
Gender differences in the body clock have implications for life threatening illnesses ranging from cancer, heart disease and diabetes to dementia.
It controls hormones, cardiovascular function and metabolism. This complex system defines your physical performance at different times of the day.
Chronic disruptions include to human circadian rhythms include shiftwork and repeated long distance travel.
Dr Anderson added: ‘These affect health and well-being and have been linked to various cardiometabolic diseases and cancer.
‘Recent findings in both humans and animal models have produced compelling evidence suggesting considerable sexual differences.
‘Females appear to be more resilient to body clock disruption, such as disruptions resulting from shift work or frequent time zone changes.
‘Also, they generally have higher peaks of activity earlier in the day than males, which is similar to the circadian patterns of children.’
They added studies tracking night shift workers, such as air stewards and stewardesses, over years will be needed to address the theory women are better suited to shift work and long distance travel.