Introduction Reports suggest increasing multiple sclerosis (MS) prevalence, which distinctively rises with latitude. Genetic factors contribute but vitamin D deficiency is a possible co-factor.
In Ireland, vitamin D is lower in MS patients than in controls.
Greater prevalence at higher latitudes corresponds to lower vitamin D levels.
Prevalence is greater than in 2001.
Patients and Methods Patients and controls in Donegal, Wexford and South Dublin attended research clinics from November 2007 to March 2008. Blood samples were taken for vitamin D and PTH measurement, and DNA extraction.
Results Prevalence significantly increased in Donegal (northwest) (290.3/100 000) compared with 2001 (184.6/100 000, p<0.001). Prevalence is significantly higher in Donegal than in Wexford (southeast) (144.8/100 000, p<0.0001) and South Dublin (127.8/100 000, p<0.0001). Overall, mean vitamin D levels were low and did not differ significantly between patients (38.57 nmol/l) and controls (36.41 nmol/l; winter normal >50 nmol/l). However, more patients had vitamin D levels <25 nmol/l, p 0.004. Levels were significantly higher in South Dublin (area with lowest MS prevalence) (mean 50.74 nmol/l, p<0.0001). HLA DRB1*15 occurred most frequently in Donegal.
Conclusion Vitamin D insufficiency is common in Ireland. Latitudinal variation in MS probably relates more to genetic factors than to vitamin D levels alone, but risk may be modified by vitamin D in genetically susceptible individuals.
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