Vitamin D is a nutrient normally associated with maintaining the strength of your bones and teeth. Research published in 2009 showed that low levels of the vitamin are also linked to more frequent occurrences of the common cold. As of 2011, however, evidence does not support the use of vitamin D to help fight cold symptoms.
Basics
Vitamin D occurs naturally in foods such as egg yolks, tuna, cod liver oil and beef liver. It is comes in supplement form and is frequently added to foods such as dairy products and cereal. In addition, your body makes vitamin D internally when you expose your skin to direct sunlight. Before you can use vitamin D, your body must put it through a two-stage chemical process. During the first part of the process, the vitamin is transformed into a substance called 25-hydroxyvitamin D, or 25(OH)D, the Office of Dietary Supplements explains. Your body then transforms 25(OH)D into a second substance called 1,25-dihydroxyvitamin D, or 1,25(OH)2D.
Vitamin D and Colds
People with low blood levels of 25(OH)D have a greater chance of catching a cold than people with normal levels, according to a review published in 2009 in the "Archives of Internal Medicine," which analyzed certain findings of an earlier nationwide study. For people with healthy respiratory systems, a 25(OH)D deficiency results in roughly one extra cold a year. People with respiratory problems such as asthma and chronic obstructive pulmonary disease typically suffer more colds than the average population, and a vitamin D deficiency might also drive their annual number of colds correspondingly higher.
Verified Uses
Despite the findings reported in the "Archives of Internal Medicine," in November 2010, the Institute of Medicine --- which makes official recommendations on vitamin intake levels --- noted that the only scientifically verified use for vitamin D supplements or fortified foods is the protection of bone health. Current guidelines recommend a daily vitamin D intake of 400 to 600 international units. The Institute specifically states that increasing your intake above this level won't typically provide you with any additional benefits. In fact, daily intake in excess of 4,000 IU actively increases your risks for kidney and tissue damage.
Considerations
The only way to truly determine vitamin D's cold-fighting effectiveness would be to give the vitamin to deficient individuals and study its effects, according to Dr. Adit Ginde of the University of Colorado Denver, who helped conduct the "Archives of Internal Medicine" review. The original study didn't focus on vitamin D and was not meant to produce this kind of information. The Institute of Medicine also cites a need for more detailed studies to gauge the true usefulness of the vitamin. You should consult your doctor before taking vitamin D or any other kind of supplement, and for advice in fighting and preventing colds.
References
- Office of Dietary Supplements: Dietary Supplement Fact Sheet: Vitamin D
- "Archives of Internal Medicine"; Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey; Adit A. Ginde, M.D., M.P.H., et al.; Feb. 23, 2009
- "Scientific American" magazine; Vitamin D Deficiency Linked to More Colds and Flu; Jordan Lite; Feb. 23, 2009
- Institute of Medicine of the National Academies; Dietary Reference Intakes for Calcium and Vitamin D; Nov. 30, 2010
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