"Shift Work at Young Age is Associated with Increased Risk for Multiple Sclerosis”
That’s the title of a report which will be published in the November Annals of Neurology. Researchers analyzed information derived from two epidemiological studies in Sweden, examining environmental and genetic risk factors for multiple sclerosis.
The first study, Epidemiological Investigation of Multiple Sclerosis (EIMS), involved completed questionnaires from 1343 MS patients and 2900 case controls. Mean age for disease onset was 33.4 years and mean time to diagnosis was 1.0 year. The second study, Genes and Environment in Multiple Sclerosis (GEMS), comprised 5129 cases with MS and 4509 matched controls. Mean age for disease onset was 33.0 years. These studies did not have any overlap in participants.
As both epidemiological studies included questions regarding demographic, lifestyle factors, and occupational exposures (as well as many other factors), detailed information regarding professions and workplace circumstances were obtained. These included whether individuals had worked “shift work” and at what age. In this report, shift work refers to “permanent or alternating working hours other than ordinary day work, and includes night work, day work (before 7 AM), and evening work (after 9 PM).”
My first non-musical summer job after high school was at a Target department store where I worked the floor during the closing shift. This meant that I reported to work in the late afternoon but wouldn’t be released until midnight much of the time as we clean-up, restocked, and rearranged our areas after closing. According to the definition of shift work included in this report, this is what I experienced one summer at the age of 18.
In both studies, there was a significant association between working shifts before the age of 20 years and an increased occurrence of MS. In EIMS, the odds for developing MS was 1.6:1 for those who started working shifts before age 20, compared with those who had never worked shifts. In GEMS, the corresponding odds were 1.3:1. Results were adjusted for variables including age, gender, residential area, ancestry, smoking, sun exposure habits, body mass index, and vitamin D level (EIMS only). Interestingly, no association was found between working shifts at the time of the disease onset and MS risk.
Sleep deprivation and the disruption of circadian rhythms may be contributing factors in the early exposure to shift work and increased MS risk. Researchers point out that “there is growing evidence of a bidirectional communication between circadian rhythms and the immune system.” Previous studies have shown that lymphocytes follow a circadian rhythm and sleep deprivation can severely disturb the functional rhythm of regulatory T cells and CD4+ T cells. In MS patients, CD4+ T cells have been found in acute lesions while CD8+ T cells are seen more frequently in chronic lesions.
