How harmful is irregular sleep or shift work, and what can you do about it?

Shift work and night work are associated with serious health risks. The risk of cardiovascular disease is 23% higher. The risk of type 2 diabetes is also elevated. For stroke there is a slightly elevated risk, and there is a link with cancer, but that evidence is mixed. Weight gain and a higher rate of accidents have also been reported^1,2. Because the research is observational, cause and effect are not firmly established, but the patterns are too consistent to ignore.

The effect on sleep is the most clearly demonstrated. Night shifts and early morning shifts lead to substantial sleep deprivation: an average of only five to six hours per 24-hour period. The transition from an evening shift to an early day shift produces the shortest sleep time, an average of 5.20 hours. Reaction times and alertness are at their worst at the end of a night shift. Shift workers believe they are more alert after the first night shift than later in the week, but objective measurements show they perform equally poorly on all night shifts².

Over the longer term there are also risks to mental health. In a study of more than 9,000 nurses, more than half of the shift workers experienced depression or anxiety³. Having little control over one's own schedule was associated with a significantly higher chance of burnout. Nurses who worked more than 66 night shifts in six months, or who consistently had fewer than 28 hours off between shifts, had a 70 to 89% higher chance of a sleep disorder. A large study of 195,000 people also linked shift work to accelerated biological ageing, with the highest risk among those doing irregular and permanent night shifts⁴.

What can you actually do about it? Unfortunately, the options are limited. The measure with the strongest evidence base is capping shifts at a maximum of 16 hours. This yielded an average of nearly three quarters of an hour of extra sleep per day and a measurable reduction in sleepiness⁵. Forward shift rotation, moving from day shift to evening shift to night shift, appears to reduce sleepiness, but the evidence is highly uncertain. A Cochrane review concludes outright that for most scheduling adjustments, such as compressed working weeks and greater worker input, there is insufficient high-quality evidence⁶. Better studies are needed before firm recommendations can be made.