Shiftworkers are on average 13% more likely to develop coronary heart disease (CHD) than those who work typical hours, researchers found.

The study, published in the journal Occupational Medicine, is the largest to examine the relationship between shiftwork and CHD – the narrowing of coronary arteries.

Researchers examined 21 studies covering 320,002 people, almost 20,000 of whom had CHD. The studies covered various shiftwork arrangements, including rotating shifts, consistent nightwork and non-standard daytime hours.

They found there was a 0.9% increase in the risk of developing CHD – also known as ischaemic heart disease – with every year spent in this working pattern.

The academics from Huazhong University of Science and Technology said there were three reasons why shiftwork may increase the risk of CHD:

• Shiftwork can disrupt circadian rhythms, which may affect the normal functioning of the heart.
• Shiftwork can increase stress, which can disturb the normal functioning of the body’s metabolic and hormonal systems. This in turn can lead to obesity, hypertension, high cholesterol and dysfunction of the endothelial – a thin membrane which lines blood and heart vessels.
• Other research has shown that unhealthy lifestyles such as smoking, poor diet and lack of physical exercise are more common among shift workers.

The number of people working shifts in the UK appears to be increasing. TUC analysis from October 2017 found that number of people regularly working nights increased by 260,000 in the preceding five years – a 9% rise.