Low serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D in institutionalized old people: influence of solar exposure and vitamin D supplementation.

The vitamin D status was investigated in 94 geriatric patients in a Danish long-stay ward. The influence of mobility and thus possibility of outdoor activity was studied as well as the influence of regular vitamin D intake. Serum levels of 25-hydroxyvitamin D (25-OHD) were significantly reduced in all groups compared with age-matched controls. In 50% of the patients hypocalcaemia and elevated levels of alkaline phosphatase and immunoreactive parathyroid hormone (iPTH) were found in combination with severely reduced serum 25-OHD values (less than 5 ng/ml) indicating the presence of osteomalacia. Supplementation with 400 IU vitamin D daily in the winter months resulted in significantly higher 25-OHD levels and normocalcaemia while slightly elevated levels of alkaline phosphatase and iPTH persisted. The serum concentrations of 25-OHD were highest in the subjects who were not confined to bed. In these patients the biochemical parameters reflecting osteomalacia were normal. Low serum 1,25-dihydroxyvitamin D levels were found in the patients with low 25-OHD while 24,25-dihydroxyvitamin D levels were within the normal range in all groups and correlated with 25-OHD. Daily vitamin D supplementation appears to be indicated for geriatric patients, especially when bedridden, even in countries where the nutritional vitamin D intake is high.