According to a recent study published in the Archives of Internal Medicine, people with vitamin D deficiency are 36% more likely to develop a cold or the flu compared with people who have adequate levels of vitamin D in their blood. An antimicrobial peptide, hCAP-18, is lower in people with low levels of vitamin D, and this peptide fights off infection before it can set in, setting flu and vitamin D at odds against each other.
Flu and vitamin D levels have been strongly linked in other studies as well. In April 2005 Dr. J.J. Cannell, a psychiatrist working in a men’s prison, found that patients taking high doses of vitamin D for a research study did not catch a virulent flu that spread throughout the prison, even when the prisoners in the study had contact with contagious medical personnel and fellow inmates. Dr. Cannell’s experience led him to hypothesize that the D levels in his study’s group helped to ward off flu with vitamin D and he has developed research protocols with colleagues to test the hypothesis.
The current Recommended Daily Allowance, or RDA, for vitamin D is 400 IU for adults, a fraction of the dose many researchers claim is needed for proper immune system function. Many doctors recommend 1000 IU to 2000 IU per day for adults, and more for those who do not spend 15 minutes per day, four days per week, in direct sunlight. Direct sunlight on the skin produces vitamin D, and changes in modern life have reduced the amount of time people spend with direct sunlight skin contact. People living in northern climates cannot synthesize adequate vitamin D levels from winter sunlight between November and March, making vitamin D supplementation for these regions a crucial part of public health programming. Flu and vitamin D connections may, therefore, be a result of a shift toward indoor lives, with time spent in offices, cars, and homes rather than in fields, yards, and walking.
Vitamin D and flu are a timely topic in light of the H1N1, or "swine flu" epidemic. Swine flu and vitamin D are linked in the same way as the regular seasonal flu and vitamin D. Higher levels of vitamin D in the blood help to ward off all influenza viruses, and researchers in Canada have begun clinical trials to test the relationship between swine flu, vitamin D, and infection.
Regardless of whether a patient uses vitamin D and swine flu prevention techniques, or regular flu and vitamin D supplements, the connections between this immune system modulator and the influenza virus may hold the key to treatments and cures for flu strains. Flu and vitamin D, therefore, leave much to be studied and understood, especially as swine flu makes vitamin D a worthwhile preventive tool.
