The supplementation trial, published in JAMA, showed no difference between high- and standard-dose groups in the number of laboratory- or parent-confirmed upper respiratory tract infections (URTIs), or average time to first infection.
The Canadian research team behind the study gave either 400IU or 2000IU of vitamin D3 to 700 children to test the effectiveness of different doses in reducing or preventing the incidence of URTIs.
“Daily administration of 2000 IU compared with 400 IU of vitamin D supplementation did not reduce overall wintertime upper respiratory tract infections,” said the team – who added that the findings do not support ‘the routine use of high-dose vitamin D supplementation in children’ for the prevention of viral upper respiratory tract infections – since 400IU seems to provide equal protection.
"We may have just busted a myth," commented study leader Dr Jonathon Maguire of St. Michael’s Hospital. "More is not always better."
The vitamin D Outcomes and Interventions in Toddlers (DO IT) trial was conducted in Canadian children aged between 1 and 5 years. Children enrolled in the trial were TARGet Kids! (The Applied Research Group for Kids), a unique collaboration between children's doctors and researchers from St. Michael's Hospital and The Hospital for Sick Children in Toronto.
The double-blinded randomised controlled trial (RCT) involved 700 children, half of whom were given 2000 IU per day (high dose), while half received 400 IU per day (standard dose).
Respective mean baseline blood levels of vitamin D for the two groups were 35.9 and 36.9 nanogrammes per millilitre (ng/ml) (90 and 92 nanomoles per litre (nmol/l)).
The primary outcome was the number of laboratory-confirmed viral URTIs over the winter months. Secondary outcomes included the number of influenza infections, non-influenza infections, parent-reported URTIs, time to first URTI and vitamin D levels at termination.
No significant difference was seen in either the primary outcome.
Interestingly, the number of parent-reported URTIs was actually higher in the high-dose group, although not by a statistically significant amount. Other secondary infection endpoints also showed no significant difference between the two dosage groups.
By the end of the study, vitamin D blood concentrations had increased to 48.7 ng/ml (122 nmol/l) in the high-dose group, while the standard dose group showed virtually no change group at 36.8 ng/ml (92 nmol/l).
The latter finding may suggest that 400IU may be a suitable dose for maintaining adequate status in children during winter months.
Volume 318, Issue 3, Pages 245-254. doi: 10.1001/jama.2017.8708
“Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children”
Authors : Mary Aglipay, Jonathon L Maguire et al