(HealthDay News) – High monthly doses of vitamin D do not reduce the incidence or severity of upper respiratory tract infections (URTIs), according to a study published in the Oct 3 issue of the Journal of the American Medical Association.
David R. Murdoch, MD, from the University of Otago in Christchurch, New Zealand, and colleagues randomized 322 healthy adults to receive either an initial dose of 200,000 international units (IU) oral vitamin D3, followed by 200,000 IU one month later, then 100,000 IU monthly, or placebo administered in an identical dosing regimen, for a total of 18 months.
The researchers found that baseline 25-hydroxyvitamin D (25[OH]D) level for participants was 29 (standard deviation, 9) ng/mL. Serum 25(OH)D levels increased and were maintained at greater than 48ng/mL throughout the study in participants receiving vitamin D supplementation. There were 593 URTI episodes in the vitamin D group and 611 in the placebo group; there was no statistically significant difference in the number of URTIs per participant between the groups (risk ratio, 0.97). There was also no significant difference in the number of days of missed work as a result of URTIs (mean, 0.76 days in each group; risk ratio, 1.03); duration of symptoms per episode (mean, 12 days in each group; risk ratio, 0.96); or severity of URTI episodes. When analysis was repeated by season and by baseline 25(OH)D levels, the results remained the same.
“In this trial, monthly administration of 100,000 IU of vitamin D did not reduce the incidence or severity of URTIs in healthy adults,” the authors write.