You may be at risk for a host of other diseases, not to mention being on a backwards social schedule, but rest assured: when working nights, your mental faculties are safe. Working the graveyard shift has no impact on reducing a person’s intelligence, according to a new long-term study.

Researchers from Brigham and Women's Hospital in Boston tracked the shift patterns of nearly 16,000 female nurses beginning in 1976, as part of an ongoing research project called the Nurses' Health Study.  The new analysis sought to understand middle-aged women’s mental abilities, study leader Dr. Elizabeth E. Devore said, because at that point in people’s lives, cognitive functions and memory skills are right on the brink of decline.

A raft of previous studies have found disrupting normal circadian rhythms can have adverse health effects, such as tripling the risk for prostate cancer in men, raising the risk for ovarian and breast cancer in women, and increasing both gender’s risk for type 2 diabetes. Women who frequently disrupt their circadian rhythms may also face greater risk of compromising their reproductive health.

Hospital researchers hypothesized the same underlying effects of these disorders would accelerate brain aging as well.

"While we had a good rationale for thinking this association might exist, it simply did not in this dataset," Devore told Reuters Health.

Devore and her colleagues used current reports about women’s shift habits as they were in 1988, when most women were between 58 and 68 years old, before conducting a series of memory and cognitive tests in 1995 and 2001, when subjects were all older than 70, to see if any mental declines appeared. Tests included recalling strings of numbers backwards and recalling a list of words.

No significant differences were observed after six cognitive tests were administered every two years, for a total of three points of data collection for each subject.

"There is still plenty to be concerned about regarding shift work," Jeanne M. Geiger-Brown, of the University of Maryland School of Nursing, told Reuters Health. "The problem with shift rotation is that the period between two successive shifts can be shorter than the equivalent number of hours on a day off between the same shift.”

Out of the women who participated in the study, roughly 1,000 reported doing at least 20 years of rotating shift work, while just over 6,000 had never done any. Those who reported rotating night shifts were often heavier than permanent night shift workers, and also tended to receive less education. But according to the study, published in the American Journal of Epidemiology, their relative scores on memory and intelligence were the same.

"Whether rotating or permanent, shift work can be detrimental to health, and the lifetime duration to shift work should be kept as low as possible," Geiger-Brown said. "Nurses who are concerned about the risk for cognitive decline can be assured that this risk is not elevated based on this large epidemiologic study.”

 

Source: Devore E, Grodstein F, Schernhammer E. Shift Work and Cognition in the Nurses' Health Study. American Journal of Epidemiology. 2013.