The Role of Vitamin D in Reducing Risk of Acute Respiratory Infections: Evidence from Randomized Trials. A Review.

Abstract

Vitamin D deficiency has been associated with increased susceptibility to respiratory tract infections. Several randomized controlled trials have investigated whether supplementation with vitamin D reduces the incidence of such infections. This article summarizes key findings, highlighting that vitamin D supplementation appears to provide protective benefits, particularly in individuals with low baseline levels.

Introduction

Respiratory tract infections (RTIs) remain a leading cause of global morbidity and mortality. Nutritional deficiencies are known to influence immune function, with vitamin D emerging as a potential modifiable factor. The immunomodulatory properties of vitamin D, particularly its ability to enhance innate immune responses, have been of increasing research interest in relation to RTI prevention.

Methods

The evidence summarized here is based on multiple randomized controlled trials (RCTs) and meta-analyses. Studies typically involved oral vitamin D supplementation (400–2000 IU daily or equivalent dosing schedules) compared with placebo, with follow-up ranging from several months to a year. The primary outcome was incidence of laboratory-confirmed or self-reported respiratory infections.

Results

Participants with low baseline vitamin D (<25 nmol/L) showed the strongest protective effect. Daily or weekly supplementation was more effective than large, infrequent doses. Overall, supplementation reduced the risk of at least one acute RTI by about 12–15% across pooled analyses. No significant increase in adverse effects such as hypercalcemia was observed

Discussion

These findings suggest that vitamin D supplementation can modestly reduce the risk of respiratory infections, particularly in individuals with deficiency. While the effect size is not dramatic, it highlights the importance of addressing nutritional deficiencies as part of broader public health strategies. Further research is needed to clarify optimal dosing and population subgroups that benefit most.

My Review

This study underscores the link between nutrition and immune health. I find the emphasis on daily or weekly supplementation over large, infrequent doses particularly important, as it aligns with the way the body naturally regulates vitamin D. For me, the takeaway is that vitamin D should not be seen as a cure but as part of a preventive health strategy, especially in populations with limited sun exposure. I would also like to see more trials in African populations, where vitamin D metabolism may differ due to higher baseline sun exposure but limited supplementation programs.

References

Martineau AR, Jolliffe DA, Hooper RL, et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta analysis of individual participant data. BMJ, 356, i6583. https://doi.org/10.1136/bmj.i6583

Preprint

Preprint

The Role of Vitamin D in Reducing Risk of Acute Respiratory Infections: Evidence from Randomized Trials. A Review.