Studies carried out assessing the effect of different doses of cholecalciferol (vitamin D3) on correcting serum 25-hydroxyvitamin D deficiency in healthy adults are limited and review studies are lacking. Moreover, the maintenance dose and its duration offered by these few studies are inconsistent. We performed a systematic review of randomized clinical controlled trials (RCTs) that assessed the effect of different doses of vitamin D3 on serum 25(OH)D in healthy adults. PubMed database was searched from 2010 to 2018 using the following search terms: "vitamin D deficiency", "Cholecalciferol", "vitamin D3 dose", "vitamin D supplement", "vitamin D therapy". RCTs and original articles that evaluated different doses of vitamin D3 were identified. A total of sixteen (out of 3016) acceptable studies fulfilling our inclusion criteria were included in the current systematic review. Our results revealed that supplementation with vitamin D3 had a significant positive effect in raising serum 25(OH) D concentrations. Our findings indicated that the best regimen of vitamin D3 supplement consisted of an initial large bolus dose either IM injection of 600.000 IU monthly or oral dose of 200.000 IU monthly or 50.000 IU weekly for 8 weeks, followed by a maintenance dose of 50.000 IU monthly or bimonthly. A large bolus therapeutic dose of vitamin D3, frequently or infrequently for 8 weeks, followed by long-term oral maintenance dose of 50.000 IU monthly or bimonthly optimiz and manitain vitamin D serum levels year round.

Introduction We reviewed the most effective vitamin D3 regimen for vitamin D deficiency in postmenopausal women. Material and methods We searched for studies and clinical trials conducted on healthy postmenopausal women published on PubMed from 2000 to 2018 using the term “Vitamin D deficiency” combined with the following terms: “dose”, “supplement”, “supplementation”, “cholecalciferol” or “cholecalciferol dose”. We identified 1376 articles which matched the search criteria. Based on reviewing the title and abstract, 17 articles were eligible for a full-text review. Of those, 12 manuscripts were ultimately included. Results A majority of the studies (75%) reported using daily maintenance doses which were predominantly administered orally (83.3%). Two studies reported favorable results following therapy with a single oral dose of 300,000 IU. After one month, however, 25-hydroxy vitamin D [25(OH)D] was satisfactory; both studies failed to maintain adequate responses after 60 and 90 days. One study found that loading oral doses of 50,000 IU/day for 2 weeks followed by the same doses every 2 weeks for one year were effective. Five studies employed oral doses of 800 IU/day but none of them reported that this dose was adequate. Three studies used doses of 1000 IU/day but only two of them reported positive results. Three trials examined oral doses of 2000 IU/day and another 3 studies tested oral doses of 4000-4800 IU/day. All of them reported acceptable responses that lasted with continued treatment. Conclusions Oral maintenance doses of 2000-4800 IU/day satisfactorily corrected vitamin D deficiency and maintained 25(OH)D levels in postmenopausal women with continuous therapy.