The antibiotic vitamin: deficiency in vitamin D may predispose people to infection.

In April 2005, a virulent strain of influenza hit a maximum-security forensic psychiatric hospital for men that's midway between San Francisco and Los Angeles. John J. Cannell, a psychiatrist there, observed with increasing curiosity as one infected ward after another was quarantined to limit the outbreak Although 10 percent of the facility's 1,200 patients ultimately developed the flu's fever and debilitating muscle aches, none did in the ward that he supervised.

"First, the ward below mine was quarantined, then the wards on my right, left, and across the hall," Cannell recalls. However, although the 32 men on his ward at Atascadero (Calif.) State Hospital had mingled with patients from infected wards before their quarantine, none developed the illness.

Cannell's ward was the only heavily exposed ward left unaffected. Was it by mere chance, Cannell wondered, that his patients dodged the sickness?

A few months later, Cannell ran across a possible answer in the scientific literature. In the July 2005 FASEB Journal, Adrian F. Gombart of the University of California, Los Angeles (UCLA) and his colleagues reported that vitamin D boosts production in white blood cells of one of the antimicrobial compounds that defends the body against germs.

Immediately, Cannell says, the proverbial lightbulb went on in his head: Maybe the high doses of vitamin D that he had been prescribing to virtually all the men on his ward had boosted their natural arsenal of the antimicrobial, called cathelicidin, and protected them from flu. Cannell had been administering the vitamin D because his patients, like many other people in the industrial world, had shown a deficiency:

The FASEB Journal article also triggered Cannell's recollection that children with rickets, a hallmark of vitamin D deficiency, tend to experience more infections…