Vitamin D

Vitamin D Reduces Flu and Asthma Attacks

Vitamin D supplements taken during the winter and early spring helped prevent seasonal flu and asthma attacks, according to a recent study done with Japanese school children.1 According to the study chief, Dr. Mitsuyoshi Urashima of Jikei University School of Medicine, Tokyo, the idea originated in an earlier study that examined whether vitamin D could help prevent the bone-thinning disease osteoporosis. The researchers in that study noticed that people taking vitamin D were three times less likely to report cold and flu symptoms.

Consequently, Dr. Urashima and colleagues designed their study to measure the effects of vitamin D3 supplements (given at 1,200 IUs daily vs. placebo) during a cold and flu season to a randomly assigned group of 167 6- to 15-year-old children. Vitamin D3, aka cholecalciferol, has better bioavailabilty than vitamin D2, or ergocalciferol, the form often found in many multivitamins.

Between December 2008 and March 2009, the period of the study, almost 19% of the children taking placebo caught influenza A, compared with only 11% taking vitamin D, a 42% reduction. In other words, the vitamin D group was 58% as likely to get the flu. Furthermore, Urashima et al. reported that Vitamin D suppressed asthma attacks in children with a history of asthma. Just 2 children taking vitamin D suffered asthma attacks, compared to 12 children taking placebo. According to Dr. Adit Ginde of the University of Colorado Denver School of Medicine, “This is the first time a study has been done that rigorously shows that vitamin D supplementation can reduce a type of influenza in a dedicated clinical trial.”2 Although not part of this study, Ginde led a group that published a study a year ago showing that asthmatics with lower vitamin D levels were at five times the risk for colds and flu.3

Back to the Urashima study, vitamin D did not prevent influenza type B, which tends to appear later in the flu season than the “A” flu variety, but perhaps it might. According to Ginde, if it protects against A, it is likely to protect against B. But, “The immune system fights different viruses in different ways.”2 So this needs to be examined further. However, based on the current study, giving kids vitamin D supplements during the winter may help reduce cases of influenza A. Dr. Urashima suggests that children could take 1,200 IU per day starting in September to prevent flu and asthma attacks during the flu season.


  1. Urashima M, Segawa T, Okazak M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Published March 10, 2010; doi:10.3945/ajcn.2009.29094.
  2. Wolinsky H. Vitamin D helps fend off flu, asthma attacks: study. Reuters Health Information, March 19, 2010.
  3. Ginde AA, Mansbach JM, Camargo CA Jr. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med 2009 Feb 23;169(4):384-90.

Asthma in the Inner Cities

There is an epidemic of asthma in the inner cities of America, where it is increasing by leaps and bounds. This is particularly true among African-American youth. So it is promising that in a recent study, researchers examined the prevalence of vitamin D insufficiency and deficiency among this urban subsector compared with control subjects without asthma.1 The study was conducted at an urban pediatric medical center. A group of 113 subjects, between the ages of 6 to 20 years, were examined and 91 were physician-diagnosed with asthma. An analysis of blood samples (available for 92% of the cases) found that the prevalence of vitamin D insufficiency and deficiency were significantly greater among cases than controls (86% vs 19%). Most of the urban African-American youth with persistent asthma were vitamin D deficient or insufficient.

Given the emerging associations between low vitamin D levels and asthma, along with studies showing that it may help, vitamin D should be widely distributed in urban areas, and especially to those with asthma. The price is very low and the safety is high.


  1. Freishtat RJ, Iqbal SF, Pillai DK, Klein CJ, Ryan LM, Benton AS, Teach SJ. High Prevalence of Vitamin D Deficiency among Inner-City African American Youth with Asthma in Washington, DC. J Pediatr 2010 Mar 15. [Epub ahead of print]

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