title: Randomized comparison of the effects of the vitamin D3 adequate intake versus 100 mcg (4000 IU) per day on biochemical responses and the wellbeing of patients.
abstract: BACKGROUND
  For adults, vitamin D intake of 100 mcg (4000 IU)/day is physiologic and safe. The adequate intake (AI) for older adults is 15 mcg (600 IU)/day, but there has been no report focusing on use of this dose.
  
  
  METHODS
  We compared effects of these doses on biochemical responses and sense of wellbeing in a blinded, randomized trial. In Study 1, 64 outpatients (recruited if summer 2001 25(OH)D <61 nmol/L) were given 15 or 100 mcg/day vitamin D in December 2001. Biochemical responses were followed at subsequent visits that were part of clinical care; 37 patients completed a wellbeing questionnaire in December 2001 and February 2002. Subjects for Study 2 were recruited if their 25(OH)D was <51 nmol/L in summer 2001. 66 outpatients were given vitamin D; 51 completed a wellbeing questionnaire in both December 2002 and February 2003.
  
  
  RESULTS
  In Study 1, basal summer 25-hydroxyvitamin D [25(OH)D] averaged 48 +/- 9 (SD) nmol/L. Supplementation for more than 6 months produced mean 25(OH)D levels of 79 +/- 30 nmol/L for the 15 mcg/day group, and 112 +/- 41 nmol/L for the 100 mcg/day group. Both doses lowered plasma parathyroid hormone with no effect on plasma calcium. Between December and February, wellbeing score improved more for the 100-mcg/day group than for the lower-dosed group (1-tail Mann-Whitney p = 0.036). In Study 2, 25(OH)D averaged 39 +/- 9 nmol/L, and winter wellbeing scores improved with both doses of vitamin D (two-tail p < 0.001).
  
  
  CONCLUSIONS
  The highest AI for vitamin D brought summertime 25(OH)D to >40 nmol/L, lowered PTH, and its use was associated with improved wellbeing. The 100 mcg/day dose produced greater responses. Since it was ethically necessary to provide a meaningful dose of vitamin D to these insufficient patients, we cannot rule out a placebo wellbeing response, particularly for those on the lower dose. This work confirms the safety and efficacy of both 15 and 100 mcg/day vitamin D3 in patients who needed additional vitamin D.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Toronto, Canada. rvieth@mtsinai.on.ca
authors.forename: Reinhold
authors.initials: R
authors.lastname: Vieth
authors.forename: Samantha
authors.initials: S
authors.lastname: Kimball
authors.forename: Amanda
authors.initials: A
authors.lastname: Hu
authors.forename: Paul G
authors.initials: PG
authors.lastname: Walfish