Differences in dosing and type of vitamin D supplementused are apparent and would be expected to have an effect onreported efficacy outcomes. Cholecalciferol is thought to bepreferable to ergocalciferol because of its effects on 25(OH)Dconcentrations and longer half-life.35 Nutritional supplementforms require enzymatic activation of vitamin D, which istightly regulated.3 There exists a class of synthetically derivedvitamin D receptor activators that do not require the kidney1a-hydroxylase reaction to potentiate an effect.36 Becausethese molecules are ingested in active form, they can bypassenzymatic activation and bind to the array of tissue vitamin Dreceptors, eliciting responses in target tissues without regulation.However, caution should be taken with these compoundsbecause they can have dangerous hypercalcemic andhyperphosphatemic effects in the human body. Dosage,including frequency of delivery, is another highly inconsistentarea of vitamin D therapy; particularly in relationship toquality-of-life outcomes. In the articles we reviewed, dosagesranged from 400 IU/day to a single large dose of 300,000 IU.In addition, route of delivery differs (oral vs intramuscularinjection), which would alter the absorption/metabolism ofvitamin D by the body. These discrepancies make it difficultto compare study outcomes. Consensus needs to be reachedin this area to improve methodologic quality and comparabilityof future study findings. Furthermore, the majority ofstudies reviewed were conducted in time spans of <2years.19,21,24-29,31-33 More long-term studies are needed toinvestigate the potential changes in HRQL over vitamin Dsupplement duration
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