July 16 2010 - Research led by University College, London and published in the
European Heart Journal found that working overtime is bad for the heart. The study forms part of the long-term
follow-up of more than 10 000 London office-based civil servants (the Whitehall II study). Researchers compared people
working a normal seven-hour day with those working a minimum of three hours extra. They found that this level of
overtime is associated with a 60 per cent increased risk of heart-related problems (including death due to heart
disease, non-fatal heart attacks and angina).
Dr Marianna Virtanen, epidemiologist at the Finnish Institute of Occupational Health said:
"The association between long hours and coronary heart disease was independent of a range of risk
factors that we measured at the start of the study, such as smoking, being overweight, or having high cholesterol.
"Our findings suggest a link between working long hours and increased CHD [coronary heart disease]
risk, but more research is needed before we can be confident that overtime work would cause CHD. In addition, we need
more research on other health outcomes, such as depression and type 2 diabetes."
The Whitehall II study recruited 10 308 volunteers aged 35-55 from twenty civil service departments
in 1985. The third phase (1991-1994) introduced a question on working hours. Based on an average of 11.2 years
follow-up, the current research analyses results from 4262 men and 1752 women aged between 39 and 61, up to the
most recent period for which clinical data are available (2002-2004). Researchers caution that while the cohort
includes several occupational grades it inevitably has no blue-collar or private sector workers.
Researchers identified 369 cases of fatal CHD, non-fatal heart attacks (myocardial infarctions) or
angina. After adjusting for socio-demographic characteristics (such as age, sex, marital status and occupational
grade) and 21 risk factors they found that working three to four hours overtime (but not one to two hours) was
associated with a 60 per cent higher rate of CHD compared with no overtime.
Considering possible explanations, results indicate that working overtime is associated with type A
behaviour pattern (a tendency towards aggressive, competitive, tense, time-conscious and hostile behaviour),
psychological distress (depression and anxiety) and poor sleep patterns. In addition, researchers highlight
undiagnosed high blood pressure associated with work-related stress; and "sickness presenteeism" (employees who
habitually work overtime also tend to work when ill, may ignore symptoms and not seek medical advice). Researchers
also suggest that people working overtime, but in jobs where they have more freedom over work-related decisions,
may have a lower risk of CHD. However, the current findings were independent of all of these factors.
Marianna Virtanen explained:
"We did not measure whether subsequent changes in these factors during the follow-up period altered
the association. One plausible explanation for the increased risk could be that adverse lifestyle or risk factor
changes are more common among those who work excessive hours compared with those working normal hours. Another
possibility is that the chronic experience of stress (often associated with working long hours) adversely affects
metabolic processes. It is important that these hypotheses should be examined in detail in the future."
Lead author Mika Kivimäki, professor of social epidemiology, concluded:
"At the moment there is no research on whether reduction in overtime work reduces CHD risk. Further
research on this topic is therefore needed. Our own future research will include analysing data over periods of time
to examine whether working long hours predicts changes in life style, mental health and traditional risk factors,
such as blood pressure, blood glucose and cholesterol. We hope that this research will increase understanding of
the mechanisms underlying the association between long working hours and coronary heart disease. We will also examine
whether overtime work increases the risk of depression, as recent research suggests that depression increases the
risk of coronary heart disease."
An accompanying editorial is provided by Gordon McInnes, professor of clinical pharmacology at the
Western Infirmary, University of Glasgow. While echoing researchers' caution about the specific characteristics of
the study's subjects, he nevertheless concludes that the findings may have far-reaching implications for
cardiovascular risk assessment.
Gordon McInnes said:
"These data from a large occupational cohort reinforce the notion that work stress attributable
to overtime is associated, apparently independently, with an increased risk of coronary heart disease. A trend
for risk to be related to hours of overtime worked supports this conclusion. If the effect is truly causal, the
importance is much greater than commonly recognized. Overtime-induced work stress might contribute to a
substantial proportion of cardiovascular disease. Physicians should be aware of the risks of overtime and take seriously symptoms such as chest pain, monitor and treat recognized cardiovascular risk factors, particularly blood pressure, and advise an appropriate lifestyle modification."
Quoting British philosopher Bertrand Russell, Gordon McInnes concluded:
" 'If I were a medical man, I should prescribe a holiday to any patient who considers work important'."