Randomized controlled trials have shown that taking 1000-2000 IU/day during the influenza season greatly reduce the risk of influenza and pneumonia.
There are no reports of incidence rates of influenza with respect to serum 25(OH)D levels. However, there are several indirect ways to estimate the dose-response relation.
One is to compare wintertime serum 25(OH)D levels to summertime levels since solar UVB is the primary source of vitamin D for most people.
A second is through randomized controlled trials of vitamin D supplementation and incidence of influenza.
A study in Long Island involving black post-menopausal women found a 60% reduction in influenza and common cold cases for those taking 800 IU/d and 90% reduction for those taking 2000 IU/d3.
A second study, involving 334 school children in Japan, half taking 1200 IU/d of vitamin D3, half taking 200 IU/d of vitamin D3, found a relative risk of 0.36 (95% confidence interval, 0.17, 0.79, p=0.006) for the 280 not taking additional vitamin D, i.e., a 64% reduced risk, for type A influenza4.
Each 1000 IU/d increases serum 25(OH)D levels by 6-10 ng/mL for average sized adults5.
The population mean values of serum 25(OH)D levels in the U.S. are 16 ng/mL for Black-Americans, 21 ng/mL for Hispanic-Americans, and 26 ng/mL for White-Americans6.
It appears that increasing serum 25(OH)D levels to above 35-40 ng/mL provides reasonable protection against type A influenza.
Thus, it appears that increasing serum 25(OH)D levels to above 35-40 ng/mL provides reasonable protection against type A influenza.
A recent prospective cohort study involving healthy adults in Greenwich, CT, USA (latitude 41º N) found a serum concentration of 25(OH)D of 38 ng/mL or higher was associated with a two-fold reduction in the risk of acquiring respiratory viral infections and with a marked reduction in the number of days ill with such infections compared to lower values7.
In addition to the well-known seasonality of influenza8910, during the recent A/H1N1 “swine flu” epidemic, those at greatest risk of complications following infection were pregnant women1112, Australian Aborigines13, and those obese or with diabetes or congestive heart failure12. See, also, the recent review in the New England Journal of Medicine14. All of these groups have lower serum 25(OH)D levels than that of the average population.
Pneumonia often develops in those who contract influenza1512. Pneumonia is also frequently found in children with rickets16, who are severely vitamin D deficient.
Page last edited: 17 May 2011
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- Urashima, M. Segawa, T. Okazaki, M. Kurihara, M. Wada, Y. Ida, H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May; 91 (5): 1255-60.
- Heaney, R. P. Davies, K. M. Chen, T. C. Holick, M. F. Barger-Lux, M. J. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. 2003 Jan; 77 (1): 204-10.
- Ginde, A. A. Liu, M. C. Camargo, C. A., Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009 Mar 23; 169 (6): 626-32.
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- Cannell, J. J. Vieth, R. Umhau, J. C. Holick, M. F. Grant, W. B. Madronich, S. Garland, C. F. Giovannucci, E. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec; 134 (6): 1129-40.
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- Creanga, A. A. Johnson, T. F. Graitcer, S. B. Hartman, L. K. Al-Samarrai, T. Schwarz, A. G. Chu, S. Y. Sackoff, J. E. Jamieson, D. J. Fine, A. D. Shapiro-Mendoza, C. K. Jones, L. E. Uyeki, T. M. Balter, S. Bish, C. L. Finelli, L. Honein, M. A. Severity of 2009 pandemic influenza A (H1N1) virus infection in pregnant women. Obstet Gynecol. 2010 Apr; 115 (4): 717-26.
- Hanslik, T. Boelle, P. Y. Flahault, A. Preliminary estimation of risk factors for admission to intensive care units and for death in patients infected with A(H1N1)2009 influenza virus, France, 2009-2010. PLoS Curr Influenza. 2010 Mar 9; RRN1150.
- La Ruche, G. Tarantola, A. Barboza, P. Vaillant, L. Gueguen, J. Gastellu-Etchegorry, M. The 2009 pandemic H1N1 influenza and indigenous populations of the Americas and the Pacific. Euro Surveill. 2009 Oct; 14 (42):
- Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic (H1N1) 2009 Influenza, Medical progress: Clinical aspects of pandemic 2009 influenza A (H1N1) virus infection. N Engl J Med. 2010; 362 (May 6): 1708-19.
- Britten, R. H. The incidence of epidemic influenza, 1918-19. Pub Health Rep. 1932; 47303-39.
- Banajeh, S. M. Nutritional rickets and vitamin D deficiency–association with the outcomes of childhood very severe pneumonia: a prospective cohort study. Pediatr Pulmonol. 2009 Dec; 44 (12): 1207-15.