This is a good review by Oudshoorn et al on the important subject of vitamin D in the elderly.
Vitamin D is a pleiotropic hormone. Besides the effects on classical tissues like bone and intestine, vitamin D has an effect on many more tissues. Effects of vitamin D metabolites can occur via endocrine, paracrine or autocrine mechanisms.
Ageing increases the risk of vitamin D deficiency and is associated with vitamin D resistance and less efficient intestinal Ca absorption and renal reabsorption. Vitamin D supplementation doses needed to treat vitamin D deficiency and secondary hyperparathyroidism vary considerably between individuals. This makes it necessary for clinicians to give tailored advice to patients when treating hypovitaminosis D, taking into account these age-related effects and other characteristics that influence vitamin D status and Ca homeostasis.
In general, mobile, Caucasian community-dwelling elderly, who have a varied diet, need vitamin D supplementation of 10-20 μg (400 IU – 800 IU ) /d to reach serum vitamin D levels of 50-75 nmol/l. Frail or institutionalised elderly on the other hand are suggested to need up to 50 ug (2000 IU)/). The effectiveness of this high-dose vitamin D supplementation in raising serum 250HD3 levels adequately has been demonstrated in several clinical trials. However, good evidence for the optimal dose of vitamin D supplementation in specific high-risk groups is still lacking.
Oral supplementation is the most effective intervention to treat vitamin D deficiency. Ergocalciferol is equally as effective as cholecalciferol in raising serum 250HD3 levels. Daily dosing is the most efficient interval to raise serum 250HD3 concentrations when compared with weekly or monthly administration.
Although vitamin D supplementation therapy is generally regarded as safe, cases of iatrogenic and accidental overdose with cholecalciferol have been reported. . Most safety data concerning the use of high-dose cholecalciferol supplementation come from observations in relatively young individuals. Few studies have used high-dose cholecalciferol supplementation for longer periods in frail, older patients. Frail old people, particularly the institutionalised, often have poor daily fluid intake, use diuretics and have less thirst sensation than younger persons.
All clinicians who frequently treat older patients should take a proactive approach to screening at-risk individuals for vitamin D deficiency, as this condition is still very prevalent. When treating patients for vitamin D deficiency, Ca intake should be assessed. Possible unwanted effects of long-term vitamin D supplementation and the effects of hypervitaminosis D should be studied in forthcoming trials.
Oudshoorn et al Ageing and vitamin D deficiency : effects on calcium homeostasis and consideration or vitamin D supplementation .

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