A predictive equation to guide vitamin D replacement dose in patients

Background: vitamin d is essential for bone health and probably the health of most nonskeletal tissues. vitamin d deficiency is widespread,and recommended doses are usually inadequate to maintain healthy levels. we conducted a retrospective observational study to determine whether the recommended doses of vitamin d are adequate to correct deficiency and maintain normal levels in a population seeking health care. we also sought to develop a predictive equation for replacement doses of vitamin d. methods: we reviewed the response to vitamin d supplementation in 1327 patients and 3885 episodes of vitamin d replacement and attempted to discern factors affecting the response to vitamin d replacement by conducting multiple regression analyses. results: for the whole population,average daily dose resulting in any increase in serum 25-hydroxyvitamin d level was 4707 iu/day; corresponding values for ambulatory and nursing home patients were 4229 and 6103 iu/day,respectively. significant factors affecting the change in serum concentrations of 25-hydroxyvitamin d,in addition to the dose administered,are (1) starting serum concentration of 25-hydroxyvitamin d,(2) body mass index (bmi),(3) age,and (f) serum albumin concentration. the following equation predicts the dose of vitamin d needed (in international units per day) to affect a given change in serum concentrations of 25-hydroxyvitamin d: dose = [(8.52 - desired change in serum 25-hydroxyvitamin d level) + (0.074 x age) - (0.20 x bmi) + (1.74 x albumin concentration) - (0.62 x starting serum 25-hydroxyvitamin d concentration)]/(-0.002). analysis of the dose responses among 3 racial groups - white,black,and others - did not reveal clinically meaningful differences between the races. the main limitation of the study is its retrospective observational nature; however,that is also its strength in that we assessed the circumstances seen in usual health care setting. conclusions: the recommended daily allowance for vitamin d is grossly inadequate for correcting low serum concentrations of 25-hydroxyvitamin d in many adult patients. about 5000 iu vitamin d3/day is usually needed to correct deficiency,and the maintenance dose should be ≥2000 iu/day. the required dose may be calculated from the predictive equations specific for ambulatory and nursing home patients.