People who work rotating night shifts appear to have a lower risk of Parkinson’s disease, the results of a study published in the American Journal of Epidemiology indicate. Conversely, an increased risk of developing this condition is linked to a longer average duration of sleep.

“Working rotating night shifts disrupts circadian rhythms and may have a wide range of physiologic, psychological and social effects on shift workers,” Dr. Honglei Chen, of the National Institutes of Health, Research Triangle Park, North Carolina, and colleagues write.

“In previous studies, shift work has been linked to higher risks of some chronic diseases, including cardiovascular disease and certain types of cancers,” they note, but any effect on the risk of developing Parkinson’s disease has not been investigated.

The researchers therefore evaluated data from the U.S. Nurses’ Health Study, which enrolled 84,794 female nurses, to see if there was an association between working rotating night shifts and Parkinson’s disease risk.

Nurses who reported at least 15 years of night shift work were older and more likely to be current smokers and users of nonsteroidal antiinflammatory drugs (NSAID), such as ibuprofen or naproxen, compared with those who never worked rotating night shifts.

Night shift workers also tended to drink more coffee but less alcohol and to have a higher body mass index. Women who worked night shifts slept slightly less than non-night shift workers.

A total of 181 cases of Parkinson’s disease were reported between1988 and 2000. The risk of Parkinson’s disease was 50-percent lower among women who had at least 15 years of night shift work compared with those who never worked rotating night shifts. After accounting for differences in age and smoking status, the investigators found that a longer sleep duration was associated with a higher risk of Parkinson’s disease. Compared with nurses who slept no more than 6 hours per day, those who slept 9 or more hours per day had a 84-percent increased risk.

Plausible biologic explanations for these results are lacking, Chen’s team points out. They note that shift work has been associated with modest increases in blood levels of estradiol and uric acid, “both of which may be protective against Parkinson’s disease.”

Conversely, they suggest that the data could be interpreted as showing that a “low tolerance for night shift work is an early marker of Parkinson’s disease.”

SOURCE: American Journal of Epidemiology, April 2006.