Urashima 2010.

Methods	Randomised, double‐blind, placebo‐controlled, parallel‐group trial Multicentre, 24 weeks long Run‐in period: Not described, concomitant medication continued 96 were lost to follow‐up, no reasons provided Study analysed on ITT basis
Participants	12 hospitals in Japan N = 430. 242 m, 188 f. Mean age 10.2 yrs, range 6 to 15 yrs Number with diagnosed asthma: 110 Inclusion criteria: Schoolchildren aged 6 to 15 yrs. With or without underlying diseases. Exclusion criteria: Had a history of stones in the urinary tract or diseases of calcium or bone metabolism. Was already taking vitamin D3 or activated vitamin D as a treatment of an underlying disease. Had a history of allergic reactions to ingredients in the tablets. Had difficulties swallowing tablets. Had been receiving immunosuppressive therapy including oral corticosteroids or chemotherapy within the past year. Were considered incapable of taking part in the study by the paediatrician in charge.
Interventions	Treatment (n = 217): 3 tablets twice daily (total: 1200 IU vitamin D3/day). Control (n = 213): 3 tablets twice daily (placebo tablets identical in appearance). Those with asthma on treatment n = 51. Those with asthma on placebo n = 59. Vitamin D status not assessed
Outcomes	Primary outcome: Influenza A, diagnosed by influenza antigen testing. Secondary outcomes: Influenza B diagnosed via nasopharyngeal swab. Physician‐diagnosed asthma attack that included wheezing improved by inhalation of a beta‐stimulant in children who already had a diagnosis of asthma. Non‐specific febrile infection in those who were not suspected to have influenza as well as other specific diseases. Gastroenteritis with 2 of 3 symptoms (nausea or vomiting, diarrhoea, or fever > 37ºC). Pneumonia diagnosed with chest X‐ray. Admission to the hospital for any reason.
Notes	Funded by the Jikei University School of Medicine. None of the authors had any conflicts of interest
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated sequence
Allocation concealment (selection bias)	Low risk	Allocation was concealed from staff and participants. Randomisation code was kept by independent data management committee and was not revealed to staff or participants until the trial was complete (information from trial report and principal investigator)
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind, placebo‐controlled study
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Double‐blind, placebo‐controlled study
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Rates of loss comparable between arms for the trial as a whole (50/217 intervention arm, 46/213 control arm), but not reported for subgroup of participants with doctor‐diagnosed asthma
Selective reporting (reporting bias)	Low risk	Nil to suggest selective reporting: outcomes listed in Methods are reported in Results. However, the trial protocol was not accessed
Other bias	Low risk	Nil