Many occupations can make you feel like you are losing your mind, but new evidence suggests that long working hours may actually lead to cognitive decline. Notably, cognitive impairment in midlife is already established as a risk factor for Alzheimer’s Disease and other forms of dementia. A new report from the Whitehall II Study, published in the American Journal of Epidemiology finds that long working hours in midlife are associated with a decline of cognitive function, and possibly dementia.

Earlier studies from the Whitehall Study group and related evaluations reported that long working hours are associated with cardiovascular and immunologic disorders, reduced sleep quality and duration, unhealthy lifestyle choices, and overall adverse health outcomes. Data examining the association between work hours and cognitive function is scarce, but the current study attempted to evaluate the link, since risk factors in midlife are important predictors of dementia in late life. For the cross-sectional study of 248 automotive workers in Britain, participants completed numerous tests related to memory and vocabulary, as well as general health, psychological well being, and physical functioning. People who worked more than 55 hours per week had significantly lower scores on vocabulary and reasoning tests at baseline and follow-up 5 years later, compared with those who worked 35 to 40 hours per week. The results were not changed when confounding factors were considered, including age, sex, marital status, education, occupation, income, and health risk factors.

Similar studies have concluded that it may not just be the total number of hours worked, but the length of shifts, that predict poor cognitive function. For example, reasoning and alertness is decreased in employees working 9- and 12-hour shifts compared to employees working more traditional 8-hour shifts. However, comparisons of total work hours and length of shift on cognitive function have not been completed. Additionally, long working hours are associated with sleep disorders, including difficulty falling asleep and early morning awakenings. Sleep disorders also contribute to cognitive decline and are a risk factor for dementia.

The generalizability of the latest findings is limited due to a small sample size that was not representative of a large population. Also, a 5-year follow-up period may not be long enough to accurately detect cognitive decline after middle age. Further, no study has isolated the causal relationship between long working hours and cognitive function. Are long working hours associated with education attainment, level of physical activity, or amount of job stress, and could these be the association with deceased cognitive function? Still, identifying risk factors for cognitive decline that may be modifiable can lead to at-risk persons maintaining cognitive function and preventing dementia later in life.

References

Elovainio, M., Ferrie, J., Singh-Manoux, A., Gimeno, D., De Vogli, R., Shipley, M., Vahtera, J., Brunner, E., Marmot, M., & Kivimaki, M. (2009). Cumulative exposure to high-strain and active jobs as predictors of cognitive function: the Whitehall II study Occupational and Environmental Medicine, 66 (1), 32-37 DOI: 10.1136/oem.2008.039305

Elovainio, M., Kivimaki, M., Ferrie, J., Gimeno, D., De Vogli, R., Virtanen, M., Vahtera, J., Brunner, E., Marmot, M., & Singh-Manoux, A. (2009). Physical and cognitive function in midlife: reciprocal effects? A 5-year follow-up of the Whitehall II study Journal of Epidemiology & Community Health, 63 (6), 468-473 DOI: 10.1136/jech.2008.081505

Virtanen M, Ferrie JE, Gimeno D, et al. Long working hours and sleep disturbances: the Whitehall II prospective cohort study. Sleep. Jun 1 2009;32(6):737-745.

Virtanen, M., Singh-Manoux, A., Ferrie, J., Gimeno, D., Marmot, M., Elovainio, M., Jokela, M., Vahtera, J., & Kivimaki, M. (2008). Long Working Hours and Cognitive Function: The Whitehall II Study American Journal of Epidemiology, 169 (5), 596-605 DOI: 10.1093/aje/kwn382

Wilson, R., Hebert, L., Scherr, P., Barnes, L., Mendes de Leon, C., & Evans, D. (2009). Educational attainment and cognitive decline in old age Neurology, 72 (5), 460-465 DOI: 10.1212/01.wnl.0000341782.71418.6c

Yaffe, K., Fiocco, A., Lindquist, K., Vittinghoff, E., Simonsick, E., Newman, A., Satterfield, S., Rosano, C., Rubin, S., Ayonayon, H., Harris, T., & , . (2009). Predictors of maintaining cognitive function in older adults: The Health ABC Study Neurology, 72 (23), 2029-2035 DOI: 10.1212/WNL.0b013e3181a92c36