SAN DIEGO, CA—Study findings suggest that 25-OH vitamin D levels <30ng/mL “may have a modest impact on the severity of influenza-like illness (ILI) in healthy adults,” researchers reported at IDWeek 2015.

Current data on the impact of vitamin D levels on viral infections have shown mixed results. Researchers from the Madigan Army Medical Center, in Tacoma, WA, and colleagues conducted a study to assess the correlation between vitamin D concentration and symptom severity.

Otherwise healthy adults (n=682) across 5 U.S. military medical treatment facilities presenting within 72 hours of symptom onset were recruited in the prospective longitudinal study of ILI. Patient 25-OH vitamin D concentrations were obtained from acute serum samples and classified as “sufficient” (≥30ng/mL), “insufficient or deficit” (<30ng/mL), or “deficient” (<15ng/mL).

“The prevalence of vitamin D insufficiency and deficiency over a wide geographic network was very high in our otherwise healthy adult population with ILI,” study author Matthew Robles, DO, reported. Nearly 78% of enrolled adults (529/682) had vitamin D concentrations <30ng/mL, including 133 patients who were vitamin D deficient.

Factors associated with increased risk of vitamin D deficiency or insufficiency included male gender, 84% vs. 68% for females (P<0.001); being non-Caucasian, 85% vs. 74%; P<0.001), and being obese (85% vs. 73%; P<0.001). “There were no difference in risk of vitamin D deficiency/insufficiency for current smokers and those who were morbidly obese,” he noted. Mean serum 25-OH vitamin D levels were significantly lower in men, non-Caucasian, the obese, and the morbidly obese (all P<0.001).

Study authors collected nasopharyngeal swabs on Day 0 (enrollment), 3, 7, and 28 and evaluated the viral etiology by PCR. Patients documented symptom severity via diary for an additional 7 days. Calculations included severity scores for lower respiratory, gastrointestinal, composite, and systemic symptoms.

Subgroup analyses showed that increased symptom severity at Day 7 was seen among patients with vitamin D concentrations <30ng/mL as well as increased composite symptoms scores, by gender, for those with levels <30ng/mL. “No differences in symptom severity were observed when analyzed by viral etiology (influenza, rhinovirus, and coronavirus),” he noted.

The proportion of subjects hospitalized was higher among those with vitamin D <30ng/mL, 6.2% vs 2.7% (P=0.07), with mean vitamin D levels lower in those hospitalized vs. nonhospitalized.

“Future study is required to assess if vitamin D supplementation during acute ILI would result in lower ILI severity,” he concluded.