Night shift linked to increased risk of heart problems

People who work night shifts are at increased risk of developing an irregular and often abnormally fast heart rhythm called atrial fibrillation (AF), according to a new study led by Shanghai Jiao Tong University School of Medicine and published in the European Heart Journal.

Using information from the UK Biobank database, researchers found that the longer and more frequently that people worked night shifts over their lifetimes, the greater their risk of AF. Night shift work was also linked to an increased risk of heart disease, but not to stroke or heart failure.

The study included 286,353 people who were in paid employment or self-employed. A total of 283,657 of these participants did not have AF when they enrolled in UK Biobank, and 276,009 did not have heart failure or stroke. Information on genetic variants was available for 193,819 participants without AF, and 75,391 of them answered in-depth questions about their lifetime employment in a questionnaire sent out in 2015. During an average follow-up time of over 10 years, there were 5777 AF cases.

The researchers found that people who currently worked night shifts on a usual or permanent basis had a 12% increased risk of AF compared to people who only worked during the day. The risk increased to 18% after 10 or more years for those who had a lifetime duration of night shifts. Among people who worked an average of three to eight night shifts a month for 10 years or more, the risk of AF increased to 22% compared to daytime workers. Among participants currently working night shifts, working night shifts for 10 or more years, or working a lifetime of three to eight night shifts a month, the risk of coronary heart disease increased by 22%, 37% and 35% respectively compared to daytime workers.

“There were two more interesting findings,” said study co-leader Professor Lu Qi, of Tulane University School of Public Health and Tropical Medicine. “We found that women were more susceptible to atrial fibrillation than men when working night shifts for more than 10 years. Their risk increased significantly by 64% compared to day workers.

“People reporting an ideal amount of physical activity of 150 minutes a week or more of moderate intensity, 75 minutes a week or more of vigorous intensity, or an equivalent combination, had a lower risk of atrial fibrillation than those with non-ideal physical activity when exposed to a lifetime of night shift work. Thus, women and less physically active people may benefit particularly from a reduction in night shift work.”

The researchers adjusted their analyses for factors that could affect the results, such as age, sex, ethnicity, education, socioeconomic status, smoking, physical exercise, diet, body mass index, blood pressure, sleep duration and chronotype (whether someone was a ‘morning’ or an ‘evening’ person). They also investigated whether genetic predisposition to AF could play a role in the increased risk but found this did not affect the link between working night shifts and AF risk, regardless of whether participants had a low, medium or high genetic risk.

A strength of the study is its size, with detailed information on over 283,000 people. Limitations include the fact that it cannot show shift work causes heart problems, only that it is associated with them; some cases of atrial fibrillation may have been missed; lifetime employment was assessed only when people joined UK Biobank and was self-reported; there may be unknown factors that might affect the results; and the people in UK Biobank were mainly white British and so it may not be possible to generalise the findings to other ethnic groups.

“Although a study like this cannot show a causal link between night shifts and atrial fibrillation and heart disease, our results suggest that current and lifetime night shift work may increase the risk of these conditions,” said study co-leader Professor Yingli Lu, of Shanghai Jiao Tong University School of Medicine.

“We plan to analyse the association between night shift work and atrial fibrillation in different groups of people. This may strengthen the reliability of these results and serve as a warning to groups working in certain types of occupations to get their hearts checked early if they feel any pain or discomfort in their chests.”

The news comes shortly after Charles Sturt University scientists announced the results of their own research into the effect that shift work in general can have on cardio-metabolic health, with the aim of establishing potential disease mechanisms.

A total of 87 ‘healthy’ males in the Bathurst region were divided into two categories: those currently employed in rotational shift work and non-shift counterparts. Testing was conducted to assess cardiovascular and metabolic functions before the results were analysed to determine the effect of shift work on health.

Findings indicate that when employees are matched for lifestyle and behavioural co-factors, including current health status, sleep quality and physical activity, employment in rotational shift work significantly increases markers of future cardio-metabolic disease risk. Shift workers took longer to metabolise a glucose dose and averaged an additional five kilograms of fat mass, which are both considered risk factors for the development of cardio-metabolic disease.

“Shift work is associated with increased fat mass, inflammatory markers and glucose metabolism compared to non-shift counterparts,” said PhD candidate Blake Collins, who conducted the research together with his supervisors.

Collins said his findings justify further research into health interventions among shift workers, with exercise having previously demonstrated health benefits in cardio-metabolic functions; however, limited research in this area has been conducted among shift workers. The Charles Sturt researchers are currently investigating the effectiveness of acute and training-based exercise interventions.

Image credit: ©stock.adobe.com/au/Elnur

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