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 <30ng/mL were recruited.
Vitamin D3supplementation (600, 2000 or 4000 IU/day) was randomly assigned in a double-blinded manner for one year. Serum 25OHD, osteocalcin (total and undercarboxylated), amyloid beta, parathyroid hormone (PTH) and estradiol were analyzed before and after supplementation. Cognitive tests were administered after treatment. The women (58±6 years; body mass index, BMI, 30.0±3.5 kg/m2) had a baseline serum 25OHD was 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, 2000 and 4000 groups, respectively (p<0.001).
Subjects taking 2000 IU/day compared to other doses performed better in learning/memory tests (p<0.05), yet the 4000 group had a slower reaction time (RTI) compared to the 600 IU/d group. Multiple regression indicated that serum undercarboxylated osteocalcin predicted tasks associated with RTI and executive function, whereas BMI and PTH negatively predicted RTI and executive function (p≤0.01).
These data suggest that vitamin D has differential effects on domain-specific cognitive measures and that a higher dose may negatively impact reaction time.
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