“Working more than eight hours a day raises the risk of heart disease by 80%,” reported the Daily Mail.
The news is based on a study that pooled the results of previous studies looking at the association between “longer working hours” and coronary heart disease (CHD). Those working longer hours were shown to be 80% more at risk of CHD.
However, there were significant inconsistencies between the studies that cast serious doubt on the validity of any conclusion about a link between CHD and working hours. These inconsistencies included the definitions of “longer working hours” (from 40 to 65 hours a week).
The studies were also inconsistent in their type, making the overall pooling inappropriate. When the researchers removed less well-designed studies from their analysis, the estimate was lower; in the region of 40% increased risk.
Finally, as only one of the studies was from the UK, the findings may not be applicable to workers in this country.
This study suggests that those who work longer hours may have an increased risk of CHD, but stops well short of proving that one causes the other. There are many other factors that may influence this association.
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The study was carried out by researchers from the Finnish Institute of Occupational Health and was funded by numerous charity and academic institutions, including the British Heart Foundation and the Medical Research Council. No conflicts of interest were declared by the study authors.
The study was published in the peer-reviewed American Journal of Epidemiology.
The Mail’s headline, "Working more than eight hours a day raises the risk of heart disease by 80%," was misleading and inaccurate. The study's 80% figure related to a range of definitions of long working hours, only some of which defined this as more than eight hours a day (a 40-hour, 5-day week). Others defined this as significantly more (more than 65 hours a week).
However, The Sun pointed out that the risk found in this study could be between 40% and 80%.
A systematic review and meta-analysis is an effective way of pooling the findings of multiple studies aiming to answer similar research questions into one summarised result.
The quality of the systematic review and meta-analysis is inherently dependent on the quality of the studies it includes. How thorough it has been in identifying all the relevant research literature to include in the first place is also important.
The researchers hypothesised that people working longer hours are more likely to be exposed to high job demands and to have less time for recreational activities and exercise than their counterparts who work fewer hours. Consequently, long working hours may be associated with CHD events such as heart attacks and angina. They reported that CHD is currently a leading cause of death, and that projections indicated that this would continue for the next several decades.