In the first longitudinal study to explore this possible connection, Knekt and colleagues analyzed data from the Mini-Finland Health Survey, which was carried out between 1978 and 1980.
Participants provided information on socioeconomic background, medical history, and lifestyle; serum levels of 25-hydroxyvitamin D were determined by radioimmunoassay.
Among the 3,173 participants included in the analysis, there were 50 incident cases of Parkinson’s disease during a 29-year follow-up.
A significant inverse association was seen between age- and sex-adjusted levels of 25-hydroxyvitamin D and Parkinson’s disease, with the relative risk between the highest and lowest quartiles of serum concentration of the vitamin being 0.35 (95% CI 0.15 to 0.81, P for trend=0.006).
The association persisted after adjustment for body mass index, leisure-time physical activity, month of blood draw, education, marital status, smoking, and alcohol consumption.
Participants whose serum concentration of the vitamin was at least 50 nmol/L had a 65% lower risk than those whose levels were below 25 nmol/L.