Disturbances of calcium or vitamin D metabolism have been suggested to be of pathogenetic importance both for hypertension and impaired glucose tolerance, two disorders that are commonly associated. In the present study 65 men, aged 61-65 years, with impaired glucose tolerance were enrolled in a prospective, double-blind, placebo-controlled study over 12 weeks evaluating the effects of 0.75 microgram alphacalcidol, a synthetic analog to the active metabolite of vitamin D. In the 26 patients with blood pressure greater than or equal to 150/90 mmHg before treatment a significant reduction (p less than 0.01) of both the systolic (SBP) and diastolic (DBP) blood pressure was found after therapy (from 171/95 to 150/88 mmHg). The effect was additive to concomitant antihypertensive treatment and was correlated (p = 0.03) to a reduction of serum levels of parathyroid hormone. Also in the whole group of patients given alphacalcidol blood pressure was moderately lowered from a mean of 152/87 +/- 22/10 (SD) to 143/84 +/- 17/8 mmHg. There were no relationships between the changes in body weight, blood glucose or insulin parameters and the changes in blood pressure during the trial. The findings are compatible with the concept that calcium metabolism influences blood pressure regulation and suggest that supplementation with a physiologic dose of active vitamin D could be beneficial for patients with high blood pressure.