Reduced vitamin D levels are a prevalent clinical finding that is clearly associated with increased morbidity and mortality. There is considerable controversy, however, as to how much vitamin D is required for the effective vitamin D replenishment in patients with reduced vitamin D levels.
Therefore, we decided to evaluate the effectiveness of 1000 to 3000 U qd of vitamin D and of vitamin D receptor agonists (VDRA) in 161 patients with vitamin D levels ≤25 nmol/l (group A) and 104 patients with vitamin D levels of 2650 nmol/l (group B). 209 of the patients were women and 56 men (mean age, 47±1 years (S.E.M.)). All patients had normal kidney function but GGT was higher in group A (31±3 vs 21±1 U/l, P<0.05). Reduced vitamin D levels were associated with lactose intolerance (40% of patients), fructose malabsorption (24%), pancreatic insufficiency (12%) and coeliac disease and/or IgA deficiency (11%). Calcium and phosphate in serum, PTH and 25-OH-vitamin D levels or 1,25-OH-vitamin D levels, respectively, were measured by routine methods.
19% of the untreated patients had hypocalcaemia and 28% had secondary hyperparathyroidism (SHPT). 3000 U of vitamin D resulted in vitamin D levels >50 nmol/l in 82% of the patients in group B but only in 54% of the patients in group A (P<0.01). Accordingly, SHPT was controlled in 94% of the patients in group B but only 85% of the patients in group A. VDRA controlled SHPT in 98% of patients in group A (P<0.05). In both groups, 1000 and 2000 U of vitamin D were less effective in normalizing vitamin D or calcium levels and in correcting SHPT (P<0.001). There was no case of hypercalcaemia or increased vitamin D or VDRA levels in the course of the study.
In patients with reduced vitamin D levels, vitamin D doses up to 3000 U/day or VDRA, respectively, are required to safely and effectively normalize vitamin D levels, to control prevalent hypocalcaemia and SHPT and to, presumably, prevent its sequelae.