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Night shift work may increase risk for MS

Working night shifts for many years increases a person’s risk for multiple sclerosis (MS), a new study has found.

Published in the journal Occupational and Environmental medicine, the study found that occasional or rotating night shift work, even if done for ten years, does not appear to increase the risk, but that working night shifts for 20 or more years increased the chance of a diagnosis threefold.

Researchers from the Medical University of Vienna studied the data of 83,992 women who were part of the Nurses’ Health Study (NHS) and 114,427 women who were part of the Nurses’ Health Study II (NHSII). Overall, there were 407 confirmed cased of MS. These nurses, recruited in 1976 for the NHS and 1989 for the NHSII, completed a health questionnaire every two years giving information on lifestyle and overall health conditions.

Analysis of the data found that there was no significant association with rotating night shifts, which were defined as three or more nights each month, and risk of MS. But once the nurses had worked rotating shifts for more than 20 years, they were 2.6 times more likely to be diagnosed with MS.

Researchers said that either long-term or early career circadian rhythm disruption might be a risk factor for MS. The circadian rhythm is the 24 hour cycle all cells of the body follow, but it can be disrupted by doing things at the ‘wrong’ time, for example being in a brightly lit environment at night time when we should be in darkness. Circadian rhythm disruption is already thought to be a risk factor for conditions like type 2 diabetes and coronary artery disease. Researchers suggest that night workers may benefit from preventive measures and disease screening programs at the workplace at early career stages.

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