Three-year follow-up of serum 25-hydroxyvitamin D, parathyroid hormone, and bone mineral density in nursing home residents who had received 12 months of daily bread fortification with 125 μg of vitamin D₃.

BACKGROUND: We conducted a single-arm clinical trial in institutionalized seniors, on the effects of high-dose vitamin D3-fortified bread daily intake (clinicaltrials.gov registration NCT00789503).

METHODS: At 1 and 3 years after the dietary fortification was stopped, serum 25-hydroxyvitamin D (25(OH)D), parathyroid hormone (PTH) and bone mineral density were measured in 23 of the original study subjects, aged 60-82 years who had consumed bread buns (100 g) fortified with 320 mg elemental calcium and 125 μg (5,000 IU) vitamin D3 daily for one year.

RESULTS: At the end of the 1-year supplementation phase (receiving vitamin D3 fortified bread daily), mean (SD) serum 25(OH)D was 127.3 ± 37.8 nmol/L (baseline for this follow-up). At 1-year follow-up, the serum 25(OH)D was 64.9 ± 24.8 nmol/L (p = 0.001, vs. baseline); and at 3-year follow-up it was 28.0 ± 15.0 nmol/L (p = 0.001 vs. baseline). Serum PTH was 18.8 ± 15.6 pg/ml at baseline while at Year 3 it was 48.4 ± 18.4 pg/ml (p = 0.001 vs. baseline). Lumbar spine BMD did not change from baseline to Year 3. However, by Year 3, hip BMD had decreased (0.927 ± 0.130 g/cm² vs. 0.907 ± 0.121 g/cm², p = 0.024).

CONCLUSION: Vitamin D nutritional status exhibits a long half-life in the body, and a true steady-state plateau may not even be reached 1 year after a discontinuation in dose. Furthermore, once the need for vitamin D has been established, based on a low baseline serum 25(OH)D concentrations, the appropriate action is to maintain corrective vitamin D supplementation over the long term.