Three Doses of Vitamin D and Cognitive Outcomes in Older Women: A Double-Blind Randomized Controlled Trial

Vitamin D may affect cognitive performance, but previous studies are either short term or observational. We conducted a randomized controlled trial of vitamin D supplementation on domain-specific cognitive measures in postmenopausal women. Overweight/obese women with serum 25-hydroxyvitamin D (25OHD) levels less than 30 ng/mL were recruited. Vitamin D-3 supplementation (600, 2,000, or 4,000 IU/d) was randomly assigned in a double-blinded manner for 1 year. Serum 25-hydroxyvitamin D, osteocalcin (total and undercarboxylated), amyloid beta, parathyroid hormone, and estradiol were analyzed before and after supplementation. Cognitive tests were administered after treatment. The women (58 +/- 6 years; body mass index, 30.0 +/- 3.5 kg/m(2)) had a baseline serum 25-hydroxyvitamin D level of 22.6 +/- 5.8 ng/mL that increased to 30.2 +/- 5.6, 36.0 +/- 4.9, and 40.8 +/- 7.0 ng/mL in the 600, 2,000, and 4,000 IU/d groups, respectively (p < .001). Participants taking 2,000 IU/d compared to other doses performed better in learning and memory tests (p < .05), yet the 4,000 IU/d group had a slower reaction time compared to the 600 IU/d group. Multiple regression indicated that serum undercarboxylated osteocalcin predicted tasks associated with reaction time and executive function, whereas body mass index and parathyroid hormone negatively predicted reaction time and executive function (p <= .01). These data suggest that vitamin D has differential effects on domain-specific cognitive measures and that a higher dose may negatively affect reaction time.