Vitamin D Levels May Be Inversely Linked With Recent Upper Respiratory Tract Infection

February 24, 2009

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February 24, 2009 — Serum 25-hydroxyvitamin D [25(OH)D] levels are inversely associated with recent upper respiratory tract infection (URTI), particularly in those with respiratory tract diseases, according to the results of a secondary analysis of the Third National Health and Nutrition Examination Survey reported in the February 23 issue of the Archives of Internal Medicine.

"Recent studies suggest a role for vitamin D in innate immunity, including the prevention of respiratory tract infections (RTIs)," write Adit A. Ginde, MD, MPH, from University of Colorado Denver School of Medicine in Aurora, and colleagues. "We hypothesize that serum...25(OH)D levels are inversely associated with self-reported recent...URTI."

The investigators conducted a probability survey of the US population performed between 1988 and 1994 and evaluated the association between 25(OH)D levels and recent URTI in 18,883 participants 12 years or older, both with and without adjustment for demographic and clinical factors including season, body mass index, smoking history, asthma, and chronic obstructive pulmonary disease (COPD).

Median serum 25(OH)D level was 29 ng/mL (interquartile range, 21 - 37 ng/mL). Recent URTI was reported by 19% of participants overall (95% confidence interval [CI], 18% - 20%), by 24% of those with 25(OH)D levels less than 10 ng/mL, by 20% of those with levels of 10 to less than 30 ng/mL, and by 17% of those with levels of 30 ng/mL or more (P < .001).

Lower 25(OH)D levels were independently associated with recent URTI, even after adjustment for demographic and clinical factors (vs 25[OH]D levels ≥ 30 ng/mL: odds ratio [OR], 1.36; 95% CI, 1.01 - 1.84 for < 10 ng/mL and OR, 1.24; 1.07 - 1.43 for 10 to < 30 ng/mL). Among individuals with asthma and COPD, the association between 25(OH)D level and URTI appeared to be stronger (OR, 5.67 and 2.26, respectively).

"Serum 25(OH)D levels are inversely associated with recent URTI," the study authors write. "This association may be stronger in those with respiratory tract diseases. Randomized controlled trials are warranted to explore the effects of vitamin D supplementation on RTI."

Limitations of this study include inability to control for all potential confounders or to make causal inference, primary outcome of recent URTI based on self-report, and serum samples collected at only 1 point in time.

"Although 25(OH)D levels less than 30 ng/mL and URTI were higher in the winter season, the inverse association was present throughout the year," the study authors conclude. "Individuals with respiratory tract diseases, such as asthma, who have low serum 25(OH)D levels may be even more susceptible to RTI. Vitamin D supplementation may reduce the incidence of URTI and exacerbations of respiratory tract diseases."

One of the study authors was supported by the Massachusetts General Hospital Center for D-receptor Activation Research and a grant from the National Institutes of Health, National Heart, Lung, and Blood Institute. The other study authors have disclosed no relevant financial relationships.

Arch Intern Med. 2009;169:384-390.


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