The association between vitamin D intake and the prevalence and mortality of asthma in the US adults

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BACKGROUND: The relationship between vitamin D intake and asthma prevalence, as well as the control of asthma symptoms, remains a contentious issue in clinical settings. This study aims to clarify the relationship between vitamin D intake and asthma outcomes. METHODS: In this study, three logistic regression models were employed to investigate the association between vitamin D intake and the prevalence of asthma. And a generalized additive model with a smoothing spline were utilized to explore the linear association. Additionally, subgroup analyses were conducted to assess potential effect modification by various factors. For asthmatic patients, the cox proportional hazards models were used to examine the relationship between vitamin D intake and mortality outcomes. And the restricted cubic splines were applied to assess non-linear relationships and threshold effect analyses were conducted to identify potential optimal levels of vitamin D intake that could significantly impact the risk of death from asthma. The data for this analysis were sourced from the National Health and Nutrition Examination Survey database. RESULTS: The logistic regression analyses revealed a significant inverse association between vitamin D intake and asthma prevalence, with each unit increase in logarithmic vitamin D intake (Log VITD) associated with an 8% decrease in the risk of asthma (OR = 0.92, 95% CI: 0.86, 0.98, p = 0.02). Subgroup analyses showed a more pronounced inverse association in males (OR = 0.79, 95% CI: 0.71, 0.88, interaction p-value < 0.01). In the cohort of asthmatic patients, a non-linear relationship between vitamin D intake and all-cause mortality was identified, with inflection points at Log VITD values of 5.36 and 6.52. For respiratory disease mortality, an inflection point at Log VITD 5.48 was found, below which increasing vitamin D intake was associated with decreased respiratory disease mortality (HR = 0.01, 95% CI: 0.00, 0.05, p < 0.01), and above which it was associated with increased mortality (HR = 45.59, 95% CI: 17.61, 118.03, p < 0.01). CONCLUSION: This study demonstrates a inverse association between vitamin D intake and the prevalence of asthma, particularly in males. In the asthmatic population, there appears to be an optimal range of the Log VITD that may reduce mortality (ranging from 5.36 to 5.48). These findings suggest that maintaining appropriate levels of vitamin D intake may be beneficial for asthma management and potentially reduce asthma-related mortality.