Vitamin D and respiratory infection risk

Circumstantial evidence implicates the wintertime deficiency of vitamin D from too little sunlight, with an increase in colds and flu.

Researchers from Denver, Colorado and Boston, Massachusetts looked for an association.

First, the details.

• Results from the Third National Health and Nutrition Examination Survey (NHANES III) were reviewed.
• The survey included 18,883 participants.
• Blood levels of 25-hydroxyvitamin D (25OHD) — the best measure of vitamin D status — were compared with the incidence of upper respiratory tract infections.
• Confounding factors (season, body mass index, smoking history, asthma, and chronic obstructive pulmonary disease) were considered in the review.

And, the results.

• Those with the lowest vitamin D blood levels — less than 10 ng per milliliter of blood — were about 40% more likely to report a recent respiratory infection vs those with vitamin D levels of 30 or higher.
• The association was present in all seasons.
• The association was stronger in those with a history of asthma or chronic obstructive pulmonary disease (COPD), including emphysema.
  • Asthma patients with the lowest vitamin D levels were 5 times more likely to have had a recent respiratory infection.
  • Among COPD patients, respiratory infections were twice as common among those with vitamin D deficiency.

The bottom line?
The authors concluded that those with the lowest blood levels of vitamin D were at greatest risk of getting a respiratory tract infection.

Next step? Another study where participants are followed in real time, say the authors.

3/1/09 23:09 JR