Major Finding: Overtime work of 3–4 hours per day was associated with a 1.6-fold increase in the risk of CHD.
Data Source: A study of 4,262 men and 1,752 women.
Disclosures: Dr. McInnes declared no conflicts of interest. The Whitehall II study was funded by the Academy of Finland and grants from the British Heart Foundation, the European Science Foundation, and the BUPA foundation; none of its authors declared conflicts of interest.
People who work 11 or more hours per day have a 60% higher risk of developing coronary heart disease than do those who work normal 7- or 8-hour workdays, according to researchers in Finland and Britain.
The findings were derived from the Whitehall II study, a long-running cohort of civil-service workers in London. The cohort included people at all occupational grades and levels of responsibility; however, none of the labor was considered blue collar.
For their research, epidemiologist Marianna Virtanen, Ph.D., of the Finnish Institute of Occupational Health, Helsinki, and University College London, and her colleagues examined data from 4,262 men and 1,752 women, aged 39–61 years (mean age 48.7 years), who were recruited into the Whitehall II cohort between 1991 and 1994 and followed for an average of 11.2 years.
All the study subjects, in addition to answering detailed questionnaires on health and lifestyle factors and undergoing clinical examinations, answered questions about their work schedules and habits. Slightly less than half (46%) reported working one or more hours a day of overtime, with 617 (10%) working 3–4 hours overtime (between 11 and 12 hours total, per day).
Investigators identified 369 cases of incident fatal CHD, nonfatal myocardial infarctions, or angina in the total group of 6,014 subjects. Overtime work of 3–4 hours per day was associated with a 1.6-fold increase in the risk of CHD, and after researchers adjusted for a host of 21 social, demographic and physical risk factors (including gender, marital status, smoking, overweight, type A behavior, occupational grade, diabetes, exercise, sleep habits, alcohol intake, fruit and vegetable consumption, and high cholesterol) the researchers still found that working more than 11 hours daily contributed independently to a 1.56-fold in risk of CHD (Eur. Heart J. 2010 May 12 [doi:10.1093/eurheartj/ehq124]).
The researchers noted several other commonalities in the high-overtime group with the potential to bear on results. One was the greater incidence of type A behavior patterns and psychological distress; another was elevated levels of alcohol use.
While older research had reported an association between occupations with reported long working hours and myocardial infarction in women but not men (Int. J. Epidemiol. 1985;14:378-88), Dr. Virtanen and her colleagues found no differences in the incidence of CHD between men and women working long hours—however, “the majority of our subjects were men,” Dr. Virtanen said in an interview. “Because women usually had lower rates of cardiovascular disease, we didn't make separate analyses but rather adjusted for gender.” The people most likely to report 11-hour or longer workday, Dr. Virtanen noted, were most often men in higher-level positions.
Though Dr. Virtanen and her colleagues saw no relationship between hypertension and long working hours, they did not discount that possibility, since they had recourse only to baseline blood pressure measurements and not ambulatory blood pressure readings. They cited two Japanese studies: one indicating that work and stress-related changes in ambulatory blood pressure might be a key contributing factor to cardiovascular risk (BMJ 1998;317:775-80), and another that suggested overtime work affected ambulatory blood pressure (J. Occ. Environ. Med. 1996;38:1007-11).
Also, Dr. Virtanen said, “What we may be seeing may be extended working hours as a proxy for a kind of lifestyle in which people are competitive and want to achieve. This type A behavior reflects that pattern but of course there might be other things [that] are related—what you cannot do if you work long hours, such as make and keep doctor appointments or sleep.”
In an editorial accompanying Dr. Virtanen's study, Dr. Gordon McInnes, professor of clinical pharmacology at the University of Glasgow, Scotland, wrote that the findings “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” (Eur. Heart J. 2010 [doi:10.1093/eurheartj/ehq116]).
Work stress attributable to overtime is associated with an increased risk of coronary heart disease.
Source DR. MCINNES