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).