Now that winter is basically knocking at our door, many of us will have to face the most common and dreaded disease in America: the common cold. Upper respiratory tract infections (URTI) represent the most common reason for U.S. emergency visits and is the most widespread disease in the States (1). Since so many of us fall victim to this almost, if not definitely, yearly, most Americans want to improve their immune system so as to be less likely to contract one. And if you walk through a pharmacy you'll notice plenty of supplements touting the "immune-boosting" powers of Vitamin C, echinacea, and all sorts of other herbs and vitamins. The scientific and medical community, however, are still debating the efficacy of such supplements. Despite that, one vitamin has come to the spotlight with some very convincing evidence: vitamin D.
Vitamin D Inversely Correlated to URTI
In 2011, a large scale study was conducted in Britain to investigate the relationship between current vitamin D status (measured by 25-hydroxyvitamin D, 25(OH)D) and respiratory infections (2). It followed 6,789 Caucasian men and women all born in Britain in one week of March, 1958. The results were promising for vitamin D as a possible preventative measure against URTI.
The study, published in the British Journal of Nutrition, found that from February until September, concentrations of 25(OH)D increased, while the prevalence of respiratory infections decreased from January until August. After adjusting for lifestyle, adiposity, and socio-economic factors, "Each 10 nmol/l increase in 25(OH)D was associated with a 7 percent lower risk of infection." They also found that this inverse relationship between 25(OH)D and URTI was true across all seasons. The study also noted that the decline in the prevalence of respiratory infections by increasing 25(OH)D concentrations was true for all months, but especially during winter when the prevalence of infection was highest.
While the study did not include non-white participants and therefore cannot extrapolate their data onto non-white ethnic groups, it does confirm previous findings with regards to the relationship between vitamin D and respiratory infections.
In 2009, the first population-based study investigating the relationship between serum 25(OH)D level and URTI was conducted in the United States (2). Similar to the British cohort studied in 2011, they also found that serum 25(OH)D levels are inversely associated with recent URTI. In addition, they also found that individuals with levels less than 10ng/mL or between 10-30ng/mL had 55 percent and 27 percent higher odds of recent URTI, respectively, when compared to individuals with serum 25(OH)D levels of 30 ng/mL or more.
Again, this study was performed on current levels of 25(OH)D and not on the effects of vitamin D supplementation.
Support For Vitamin D Supplements
As of yet, there have been very few large scale, controlled studies examining the effects of vitamin D supplementation and the common cold. That being said, the evidence found in both the aforementioned studies definitely indicate the need for more randomized controlled trials of vitamin D supplements.
In 2010, a small double-blind, placebo-controlled trial was conducted in school children did find that vitamin D supplementation may reduce the incidence of influenza A (4). The trial took place from December 2008 to March 2009 in Japan and included 430 schoolchildren. The dose administered during the trial was (1200 IU/d). Despite the short timeline of the study, they did find that "vitamin D3 significantly reduced the incidence of influenza A within 60 days."
While it may be too early to jump to conclusions with regards to preventing the common cold through vitamin D supplementation, it's clear that there is a link between vitamin D levels and URTI, and as such, I would like to see more trials and studies performed on a larger scale. According to the American study (3), current recommendations for vitamin D supplementation (200-500 IU/d) are most likely unable to achieve optimal serum 25(OH)D levels (above 30 ng/ML) (3). Therefore, it's also important that dosing be considered in future trials involving vitamin D supplementation.
Hopefully with further studies exploring the role of vitamin D supplementation, we'll be able to find supplements that truly work on the shelves.
1. Burt CW, McCaig LF, Rechtsteiner EA. Ambulatory medical care utilization estimates for 2005. Adv Data. 2007;388:1-15.
2. Berry DJ, Hesketh K, Power C, et al. Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr. 2011 Nov;106(9):1433-40.
3. Ginde AA, Mansbach JM, Camargo CA, et al. Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med. Feb 23, 2009; 169(4): 384-390.
4. Urashima M, Segawa T, Okazaki M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60.