The research, which is published online Wednesday 12 May in the European Heart Journal, found that, people who worked eleven or more hours per day compared with those who worked a normal, eight-hour day had a 60% higher risk of heart-related problems such as death due to heart disease, non-fatal heart attacks and angina.
Dr Marianna Virtanen, an 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. "
The Whitehall II study started in 1985 and recruited 10308 office staff aged 35-55 from 20 London-based civil service departments. During the average 11.2 years of follow-up, Dr Virtanen and her colleagues in Finland, London and France, found that there had been 369 cases of fatal CHD (coronary heart disease), non-fatal heart attacks (myocardial infarctions) or angina. After adjusting for sociodemographic factors such as age, sex, marital status and occupational grade, they found that working 11 or more hours a day was associated with a 60% higher rate of CHD compared with no overtime work. Further adjustments for a total of 21 risk factors made little difference to these estimates.
“Our findings suggest a link between working long hours and increased CHD 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 researchers say there could be a number of possible explanations for this association between overtime and heart disease. Their results showed that working overtime was related to type A behaviour pattern (people with type A behaviour tend to be aggressive, competitive, tense, time-conscious and generally hostile), psychological distress manifested by depression and anxiety, and possibly with not enough sleep, or not enough time to unwind before going to sleep.
The senior author of the study, Mika Kivimäki, Professor of Social Epidemiology at University College London (London, UK) and Finnish Institute of Occupational Health outlined future plans for this work: “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.”
Data have been collected at regular intervals and in the third phase, between 1991-1994, a question on working hours was introduced. This current analysis looks at the results from 6014 people (4262 men and 1752 women), aged 39-61, who were followed until 2002-2004, which is the most recent phase for which clinical examination data are available.
Marianne Virtanen and Mika KivimäkiKivimäki_Mika.aspx