Bone Abstracts

Vitamin D deficiency is common in aging people and is associated with secondary hyperparathyroidism, bone loss, osteoporosis and fractures in epidemiological studies. Vitamin D₃ is produced in the skin through u.v. irradiation of the sun in spring and summer, and it can also be obtained from food, especially fatty fish, such as herring or mackerel. Vitamin D is activated by liver and kidney. Its main action is stimulation of calcium absorption from the gut. Vitamin D status is positively related to bone mineral density. Many randomized clinical trials studying the effect of vitamin D with or without calcium vs placebo have been done with fracture incidence as main outcome. About one-third of these showed a decrease of hip fracture and/or non-vertebral fracture incidence in the order of 10–20%. The vitamin D dose in these trials was 400–1000 IU/day. Many meta-analyses have been performed generally concluding to a modest preventative effect. The effect was stronger in older persons, in the institutionalized, and when baseline calcium intake and serum 25-hydroxyvitamin D were low. On the other side, an increase in fracture incidence was seen in two trials where vitamin D was given in a very high dose once per year. In some clinical trials, vitamin D with or without calcium also led to a decrease of the incidence of falling. Severe longstanding vitamin D deficiency may result in mineralisation defects and osteomalacia (English disease) but this is relatively rare. The optimal blood level of 25-hydroxyvitamin D is above 50 nmol/l. To obtain this level without sunshine exposure the vitamin D intake should be 800 IU/day.

Learning objectives: Vitamin D is produced in the skin under the influence of sunlight and can be ingested with some foods, e.g. fatty fish.

Vitamin D stimulates the absorption of calcium from the gut.

Vitamin D deficiency is related to osteoporosis and fractures.

Vitamin D and calcium supplements can decrease fracture incidence.