William B. Grant, Ph.D.
Sir:
The recent paper reporting that pregnancy women in 13 states had four times the risk of hospital admission for pandemic H1N1 2009 influenza virus than the general population1 represents a serious public health problem. While giving priority for H1N1 influenza vaccine to pregnant women and prompt treatment of such infected women is certainly indicated, it is also important to understand why pregnant women are more susceptible to this virus. It was hypothesized that epidemic influenza is largely seasonal is due to the annual variation in solar ultraviolet-B (UVB) doses and vitamin D production.2 That the infected women had a high case-fatality rate (19%), had a high fraction with Hispanic heritage, often developed pneumonia and required cesarean section delivery are also consistent with vitamin D deficiency. Case-fatality rates in the United States during the 1918-1919 influenza pandemic were generally due to subsequent pneumonia and were much higher in northern cities than in southern states, which was attributed to differences in solar UVB doses.3 Low vitamin D is also a significant risk factor for primary cesarean section delivery.4 It has been suggested that pregnant and nursing women require 4000-6000 IU/day of vitamin D,5 which is higher than 2000-4000 IU/day now considered required for the general population based on emerging scientific findings. There are many health benefits of vitamin D, so increasing vitamin D production would have many health benefits.
I receive funding from the UV Foundation (McLean, VA), the Vitamin D Society (Canada), and the European Sunlight Association (Brussels).
References
1. Jamieson DJ, Honein MA, Rasmussen SA, et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009 Jul 28. [Epub ahead of print]
2. Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006;134:1129-40.
3. Grant WB, Giovannucci D. The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918
4. Merewood A, Mehta SD, Chen TC, Bauchner H, Holick MF. Association between vitamin D deficiency and primary cesarean section. J Clin Endocrinol Metab. 2009;94:940-5.
5. Hollis BW. Vitamin D requirement during pregnancy and lactation. J Bone Miner Res. 2007;22 Suppl 2:V39-44.