Background: The aim of this study was to test the hypothesis that vitamin D supplementation improves well-being in patients with frequent respiratory tract infections (RTIs). We performed a post hoc analysis of a randomized, placebo-controlled and double-blind study in which patients with frequent RTIs were randomized to placebo or vitamin D (4000 IE/day for 1 year, n = 124). At the last visit of the study, patients were asked to perform a general assessment of their well-being during the study.
Results: The majority of patients, both placebo- and vitamin D treated, stated that they had felt 'better' during the study; 52% in the placebo group and 70% in the vitamin D group, relative risk 1.3 (95% CI 1.0-1.8; p = 0.06, Fisher's exact test). Statement of better well-being was associated with an increase in 25-hydroxyvitamin D (25-OHD) levels (p < 0.001). In contrast, worse well-being was associated with unchanged 25-OHD levels. Notably, a 25-OHD level above 100 nmol/L at the study end was associated with a higher chance of having a better well-being (p < 0.01). Four patients on anti-depressive treatment could terminate their antidepressant medication during the study. These patients had a significant increase in 25-OHD levels from low levels at study-start.
Conclusion: Vitamin D supplementation to patients with frequent RTIs might be beneficial, not only for infections, but also for their general well-being. However, given the post hoc design of this study, these findings need to be confirmed in additional clinical trials before firm conclusions can be drawn.
Trial registration: http://www.clinicaltrials.gov (NCT01131858), registered March 22, 2010.