Dose recommendation for vitamin D supplements

Unfortunately, there is no consensus on the optimal dose of vitamin D supplementation for managing viral diseases or RTI. A previous study has reported that in children suffering from recurrent respiratory tract infection, giving vitamin D supplements could reduce the number of disease occurrences in a year, with no noticeable adverse side effects, suggesting that vitamin D supplementation could be an effective adjuvant therapy in managing RTI(113). Doses ranging from 800 IU to 100,000 IU per day have been suggested(114). When using a bolus schedule, the effects seems to be smaller(115-117). Vitamin D has been shown to be beneficial in the prevention and treatment of influenza(118). Research conducted in Japan has reported that taking 1200 IU per day of vitamin D supplement could reduce the risk of contracting influenza by six fold(72). In terms of recommending dosage of vitamin D as an adjuvant therapy for influenza, it has been shown that there is a lower incidence of influenza among patients whose serum level of vitamin D is above 40ng/mL(118, 119). Besides that, by giving 50,000IU of vitamin D3 supplement once daily or 10,000IU of vitamin D three times a day, significantly reduced the severity of symptoms in patients who suffer from influenza after a period of seventy-two hours(120).
Vitamin D supplementation should ideally be guided by serum levels of vitamin D to avoid untoward effects. Recent trials challenged whether serum vitamin D levels of ≥30 ng/mL promote human health(121). A study by Quraishi et al (2013) found that people with vitamin D levels of less than 30 ng/ml were 56% more likely to develop community acquired pneumonia than those with levels of 30 ng/ml or higher(80). A recent paper by Grant et al (2020) suggested taking 10,000 IU per day of vitamin D3 for a few weeks as a loading dose, followed by 5000 IU per day as a maintenance dose, in order to raise serum vitamin D level above 40–60 ng/mL(122). Indeed, a dose of up to 4000 IU or 100 micrograms per day has been cited as a safe dose by several studies(123, 124). Public Health England (PHE) has recently recommended taking 10 micrograms of vitamin D per day as a supplement during the lockdown period(125). More randomised controlled trials and large population studies should be conducted to evaluate these recommendations(122).