SafetyInsights.org

This meta-analysis and systematic review evaluated available research on the links between shift work (SW) and long work hours (LWH) on chronic health conditions.

Not really summarising this paper as it’s open access (link in comments so you can read it yourself).

Some findings included:

Links with shift work-

·        Moderate grade evidence was found between breast cancer and SW – up to 11% heightened risk compared to non-SW

o  One study found a dose-response relationship with a 5% increase in breast cancer risk for every 5 years of shift work exposure

o  Low grade evidence was found between SW and ischaemic heart disease, myocardial infarction & ischaemic stroke. For ischaemic heart disease, the elevated risk was found for both rotating and fixed night shift work

o   Noting the low-grade evidence, a 13% increase for isachemic heart disease risk was found in SW and another found a 0.9% increase in risk per year of SW

·        Shift work on pregnancy

o   For pregnancy, SW was linked with increased risk of preterm birth and small-for-gestational-age among shift workers

o   Fixed shifts were linked with gestational hypertension (but rotating didn’t reach statistical significance). However, rotating shifts was associated with significant risk of preterm delivery

·        Shift work on other health measures

o   Very low-grade evidence was found between SW and risk of depression, diabetes, hypertension, miscarriages, occupational injuries, obesity, metabolic syndrome and other cancers – but many of these studies had high risk of bias

Links with long work hours

·        Stroke was the only outcome that met moderate grade evidence with long work hours. A 33% increased risk of stroke was found among those who worked more than 40 hours per week

·        Risk may be higher among higher socioeconomic status, but no significant difference was found by age group or sex

·        A dose-response relationship was found where longer work hours translated to proportionally higher risk – an 11% increased risk per increase in work hour category

·        Low-grade evidence was found for the links between long work hours and depression, coronary disease and some selected complications of pregnancy (preterm delivery and low birthweight)

·        One study found 14% higher odds ratios for depression in those that worked >40 hours per week

·        One study found elevated odds (14%) for coronary heart disease for those working long hours

·        For pregnancy, a 21% increased odds for preterm delivery and 43% increased odds for low birth weight were found among those working >40 hours

·        Very low-grade evidence with long work hours was found with: miscarriage, preeclampsia, gestational hypertension, small gestational age, diabetes and all studied cardiovascular diseases. Again, a high risk of bias in the studies “[casts] doubt on the significant relationships detected by these reviews”.

As expected, the quality of evidence overall was rather limited.

Also note that the direction of causality isn’t necessarily known or clear in all cases. For instance, does long working hours contribute to depression or are those with depression more likely to work longer hours? Or is it both?

Authors: Rivera AS, Akanbi M, O’Dwyer LC, McHugh M (2020) Shift work and long work hours and their association with chronic health conditions: A systematic review of systematic reviews with meta-analyses. PLoS ONE 15(4): e0231037. 

Study link: https://doi.org/10.1371/journal.pone.0231037

Link to the LinkedIn article: https://www.linkedin.com/pulse/shift-work-long-hours-association-chronic-health-ben-hutchinson