> When all studies were analysed together, no statistically significant effect of vitamin D was seen on the proportion of participants with at least one upper respiratory tract infection, lower respiratory tract infection, hospital admission or emergency department attendance for acute respiratory tract infection, course of antimicrobials for acute respiratory tract infection, or absence from work or school due to acute respiratory tract infection. However, when this analysis was stratified by dosing frequency, a borderline statistically significant protective effect of daily or weekly vitamin D supplementation against upper respiratory tract infection was seen (adjusted odds ratio 0.88, 0.78 to 1.00; 4483 participants in 11 studies, P=0.05; table 5⇓).
Which to me makes it sound like it makes almost no difference.
Edit: The above could be for pre-exsisting patients.
The paper indicates that a meta-analysis of primary effects in published research shows a significant effect, but for secondary effects in published research (those not related to study aims), no effect. Ok.
Both sorts of reports (of primary and secondary effects) have their own sorts of biases. In general, while there is tendency to only publish and report significant effects (and this applies for both primary and secondary outcomes), study design matters, and a study may not be well designed to detect, or account for other factors, for secondary outcomes- in N, choice of population, control procedures and variables used, or even how accurately and systematically that data was recorded. Does make it hard to evaluate.
Without reading the study in detail, I feel like 4,483 is too few people to detect an effect like this because you can’t easily control for how much vitamin d people get from the sun.
> When all studies were analysed together, no statistically significant effect of vitamin D was seen on the proportion of participants with at least one upper respiratory tract infection, lower respiratory tract infection, hospital admission or emergency department attendance for acute respiratory tract infection, course of antimicrobials for acute respiratory tract infection, or absence from work or school due to acute respiratory tract infection. However, when this analysis was stratified by dosing frequency, a borderline statistically significant protective effect of daily or weekly vitamin D supplementation against upper respiratory tract infection was seen (adjusted odds ratio 0.88, 0.78 to 1.00; 4483 participants in 11 studies, P=0.05; table 5⇓).
Which to me makes it sound like it makes almost no difference.
Edit: The above could be for pre-exsisting patients.