by Craig Weatherby
A flood of research into the “seafood-and-sunshine” vitamin suggests that higher-than-average blood levels provide a range of protective health benefits.
Late last year, this new evidence prompted the Food & Nutrition Board of the U.S. Institute of Medicine to triple the recommended daily allowance (RDA) for infants and adults, from 200 IU to 600 IU.
Based on the evidence and the clear safety of higher intakes, many experts wanted the RDA raised to 1000 or even 2000 IUs … still, the FNB’s step was pretty substantial.
Most of the attention has fallen on vitamin D’s apparent power to curb the risk of cancer and auto-immune disorders, build strong bones, and support heart health.
But the hormone-like nutrient also plays critical roles in immunity to infections.
Vitamin D’s overlooked part in fighting infections
Vitamin D is needed to produce “anti-microbial peptides” …powerful first-line defenders that fend off unfriendly bacteria, fungi, and viruses as they try to get through our mucous membranes and organ walls.
And there’s increasing evidence that vitamin D triggers a key part of the body’s second-line, “adaptive” (acquired) immune response (see “Vitamin D Activates Two Key Immune Systems”).
Vitamin D appears able to enhance people’s immunity to lung infections, while deficiency is associated with increased risk of tuberculosis (Martineau AR et al. 2007; Hansdottir S et al. 2008; Yamshchikov A et al. 2009).
For more on this topic, see “Vitamin D Cuts Flu Rate in First Clinical Trial,” “Flu and Colds Risk Linked to Vitamin D Lack,” and “Vitamin D May Explain the Flu… and Fight it, Too.”
Now, a cell study from Sweden suggests that higher vitamin D levels may help protect against urinary tract infections (UTIs)… a preventive health arena that’s been dominated by cranberries… especially cranberry juice and supplements.
Details of the Stockholm study
A team from Stockholm’s famed Karolinska Institute studied a small group of women, and concluded that vitamin D supplements promote localized production of anti-microbial peptides when UTIs try to invade women’s bladders.
As they wrote, “In the light of the rapidly growing problem of resistance to common urinary tract antibiotics, we suggest that vitamin D may be a potential complement in the prevention of UTI. Determining the vitamin D status of individuals with a history of UTI may be of importance to evaluate their ability to fend off intruding bacteria.” (Hertting O et al. 2010)
Their study consisted of two parts.
First, to get a sense of the vitamin D status of Swedish women, the Stockholm team analyzed vitamin D blood levels in 22 post-menopausal women and six pre-menopausal women (Hertting O et al. 2010).
Among the 22 postmenopausal women, only five had vitamin D3 levels above the widely recommended level of 75 nmol/L. One was vitamin D deficient (<25 nmol/L), nine had insufficient levels (<50 nmol/L).
Then, for a separate clinical study, they recruited eight additional women (median age 62), each of whom took 2,000 IUs of vitamin D3 daily for 12 weeks... five women completed the trial.
The researchers biopsied bladder tissue from the participants before they took vitamin D supplements and at the end of the 12 week period, and exposed both tissue samples to the E. coli bacteria that typically causes UTIs.
As hoped, the results showed increased “expression” of antimicrobial peptides in bladder tissue after women took ample amounts of vitamin D daily for 12 weeks.
Can vitamin D offer a complement (or alternative) to antibiotics?
The Swedes made two very important points about their discovery (Hertting O et al. 2010):
“In light of the emerging resistance to antibiotics used against UTI, new treatment strategies are needed. Our data suggest that vitamin D can stimulate an increased production of the antimicrobial peptide cathelicidin.”
“By inducing and activating cathelicidin with vitamin D, a local rather than a systemic effect can be achieved. This could offer selective and site-specific treatment of pathogens without perturbing commensal [friendly] microbes elsewhere in the body.”
Their second point refers to the fact that antibiotics harm beneficial bacteria in the gut and can spread throughout the body, exerting unwanted effects.
In contrast, vitamin D only produces antimicrobial peptides at the site of an infection, leaving friendly microbes untouched.
We expect—and will report—further investigations into vitamin D’s ability to help fight infections.
Hansdottir S, Monick MM, Hinde SL, Lovan N, Look DC, et al. (2008) Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense. J Immunol 181: 7090–7099.
Hertting O, Holm Å, Lüthje P, Brauner H, Dyrdak R, et al. (2010) Vitamin D Induction of the Human Antimicrobial Peptide Cathelicidin in the Urinary Bladder. PLoS ONE 5(12): e15580. doi:10.1371/journal.pone.0015580
Martineau AR, Wilkinson RJ, Wilkinson KA, Newton SM, Kampmann B, et al. (2007) A single dose of vitamin D enhances immunity to mycobacteria. Am J Respir Crit Care Med 176: 208–213.
Yamshchikov A, Desai N, Blumberg H, Ziegler T, Tangpricha V (2009) Vitamin D for treatment and prevention of infectious diseases: a systematic review of randomized controlled trials. Endocr Pract 15: 438–449.