Shift work: bad for your diet and sleep, and raises your cancer risk

Dr Muiris Houston: A body of evidence links shift work with diabetes, heart disease and cancer

In 2007 the World Health Organisation classified night shift work as a probable carcinogen due to circadian disruption

"We are such stuff as dreams are made on; and our little life is rounded with a sleep."William Shakespeare

Like most healthcare professionals, I’ve done my share of shift work. That is, I’ve worked a schedule outside the traditional 9am to 5pm day – evening shifts, early morning shifts, night shifts and rotating shifts.

My least favourite was a week of night shifts. I’m not very good at sleeping during the day, so as the week went on I would rack up quite a sleep deficit. I feared that by night six and seven I was something of an automaton.

About 15-20 per cent of workers in industrialised countries work shifts. And it’s not conducive to a healthy lifestyle. A 2016 Safefood survey found that two-thirds of Irish people doing shift work skipped meals while some eight in 10 said they weren’t getting enough sleep. It revealed younger shift workers were more likely to be overweight and to drink more alcohol. Older workers reported poorer sleep patterns and lower levels of physical activity.


There is a substantial body of evidence linking shift work with diabetes, heart disease, cancer and even a decline in brain function.

In 2007 the World Health Organisation classified night shift work as a probable carcinogen due to circadian disruption. Our bodies are programmed to run on cycles known as circadian rhythms, and changes in our routine caused by shift work disrupts those rhythms.

Over time there is a cumulative biological effect leading to disease.

One of the longest running health studies in the world is the American Nurses Health Study. Started in 1976, it has since followed the health of almost 75,000 registered nurses. Using data from the study a team of researchers investigated possible links between rotating night shift work and death from cancer and cardiovascular disease. Over a 22 year follow up period they found that working rotating night shifts for more than five years was associated with an increase in mortality from all causes.

Mortality from cardiovascular disease was 20 per cent higher for women who had spent between six and 14 years working a rotating night shift pattern. However the only association between rotating shift work and cancer was a 25 per cent higher risk for lung cancer in those who worked shift work for 15 or more years.

So shift work poses significant health risks. But is there anything shift workers can do to ameliorate these negative effects? An article last week in the British Medical Journal had some useful suggestions for those working nights. Acknowledging limited research in the area, the authors suggest the most effective approach to combating the effects of night shift work is personalised and multimodal.

They offered the following strategies:

– Minimising sleep debt before beginning a set of night shifts is a logical first step, they said, “allowing unrestricted sleep on the morning before the first shift (waking without an alarm) and supplementing sleep by napping during the afternoon.”

– Napping during a shift improves alertness and performance. But shift naps should be kept to less than 30 minutes, to avoid slow wave sleep followed by grogginess on waking.

– Prior to the end of the shift avoid caffeine and nicotine. Wear sunglasses on way home – even on cloudy days. Use public transport rather than driving.

– On the days during night shifts get to sleep as early as possible. Avoid bright lights and screens. And accept that any sleep, however fragmented is better than none.

– After the week of nights the primary goal is to reestablish a normal sleep rhythm. Immediately after the last night shift try to have either a 90 or 180 minute nap. Go outside after the nap to natural light. Go to bed at normal time that night. And avoid day time naps during the next few days.