MONDAY, Oct. 17 (HealthDay News) -- Working overnight or odd shifts may increase teenagers' risk of developing multiple sclerosis, according to the results of an observational study.
Researchers from Sweden who uncovered the link said interruption of circadian rhythms and disruption of normal sleep patterns may be partially responsible for the added risk.
In conducting the study, published in the Oct. 18 issue of Annals of Neurology, researchers examined two population-based studies of Swedish residents aged 16 to 70 (one with incident cases and one with prevalent cases) to compare the number of cases of multiple sclerosis among those who did and did not work overnight or shift hours on a regular or alternating basis during their teens.
Among the incident cases, the investigators found those who worked overnight hours for three years or more before the age of 20 were twice as likely to develop multiple sclerosis as those who never worked night shifts. Among the prevalent cases, they noted, the teens who worked overnight hours were slightly more than twice as likely to develop the disorder commonly called MS.
"Our analysis revealed a significant association between working shift at a young age and occurrence of MS," Dr. Anna Karin Hedstrom, of the Karolinska Institute in Stockholm, said in a journal news release. "Given the association was observed in two independent studies strongly supports a true relationship between shift work and disease risk."
The researchers explained the sleep restriction associated with working the night shift has already been shown to increase the risk for certain health problems, including heart disease, thyroid disorders and cancer, likely by interfering with melatonin secretion and increasing inflammatory responses.
The authors pointed out that since MS is a central nervous system autoimmune inflammatory disorder that is linked to a person's environment, other lifestyle risk factors, such as sleep loss due to shift work, should also be considered.
The study authors noted that more research is needed to explain why the disruption of circadian rhythm and sleep loss increase teenagers' risk for developing MS.
The U.S. Centers for Disease Control and Prevention provides more information on the health effects of shift work.
-- Mary Elizabeth Dallas
SOURCE: Annals of Neurology, news release, Oct. 18, 2011
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