(RxWiki News) Scientists still don't know what causes multiple sclerosis (MS). It could be viruses, genetics or environmental factors, or a combination of all three. One new study suggests it could be the kind of work people do.
The results of that study showed that dairy workers in a certain Danish population had higher rates of MS than people in other lines of work.
This research is the first to show an increased risk of MS in dairy workers.
While the researchers could not explain what caused this increased risk, they did mention previous studies that have linked cow's milk to MS.
"Know the hazards of your job."
This study, led by Henrik Horwitz, MD, of Bispebjerg Hospital at the University of Copenhagen in Denmark, was sparked by a finding that Dr. Horwitz and colleagues made some years back.
In 2006, while looking at critical illness insurance claims from a Danish pension fund, these researchers noted a high number of claims made by patients diagnosed with MS who worked in agriculture.
Critical illness insurance is an insurance plan that pays policyholders in a lump sum when they are diagnosed with a critical illness.
According to the researchers, these agricultural workers — made up of dairy workers, gardeners and agricultural assistants — had the lowest rates of critical illness in general. So why did MS seem to pop up so often?
Previous research has suggested that vitamin D, which most people get from being exposed to the sun's UV light, may protect against MS. Other research has shown an association between cow's milk and risk of MS.
For this current study, Dr. Horwitz and colleagues set out to see if gardeners or dairy workers had a higher risk of developing MS compared to other workers in PensionDenmark, a pension fund that insures more than 300,000 Danish workers.
Over the course of 10 years, 389 people were diagnosed with MS. The rate of MS among men was 10.2 per 100,000 men. Among women, that rate was 16.1 per 100,000.
The highest rate of MS was found among agricultural workers.
After looking a little deeper, the researchers found that this high rate of MS among agricultural workers could be tracked more specifically to dairy workers, who were two times more likely to develop MS than any of the other workers.
"Interestingly, dairy operators had the highest risk of developing MS, and the tendency was found both among men and women," the study authors wrote. "We were puzzled by the finding of an increased risk of MS among members of the agricultural segment of the pension fund, because this would seem to go against the vitamin D and sun exposure hypothesis. However, it became clear that dairy operators constituted one-third of this cohort, and this seemed to explain our findings."
Simply put, the researchers were surprised at first to find the increased risk of MS in agricultural workers, since many of these workers are typically outside getting that protective vitamin D from the sun. But then they saw that so many of the agricultural workers in this pension fund worked in the dairy sector, which doesn't require as much outdoor activity.
"No previous research has identified an increased risk of MS in dairy operators, so is this a coincidence? Or is it a clue to etiology (the origin or causes of disease)?" the researchers asked.
They went on to cite past research that has linked cow's milk to MS risk but concluded that this question should be studied further.
This study was published June 25 in BMJ Open.
The research did not receive any specific funding. The authors declared no competing interests.