American Journal of Epidemiology Advance Access published online on July 1, 2008
American Journal of Epidemiology, doi:10.1093/aje/kwn200
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Letter to the Editor |
THE FIRST TWO AUTHORS REPLY
1 Cancer Control Research Program, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
2 Department of Health Care and Epidemiology, University of British Columbia, Vancouver, British Columbia, Canada
(e-mail: mmcbride{at}bccrc.ca)
We thank Hanauer and Choi (1) for their interest in our study (2). They are concerned about the positive association we reported between childhood leukemia and vitamin intake in childhood and would like clarification about what constituted a vitamin supplement in the study. In addition, they are wary of the potential public health implications related to our findings, particularly regarding clinical recommendations for vitamin D supplementation to prevent rickets in exclusively breastfed infants (3, 4).
While maternal vitamin intake during pregnancy has been associated with a decreased risk of childhood leukemia (5), ours is one of the first studies to examine the effect of vitamin intake in infancy and childhood. We reported that children who received vitamin supplements during the first year of life or later were at an increased risk of leukemia (odds ratio = 1.66, 95% confidence interval: 1.18, 2.33) and acute lymphoblastic leukemia (odds ratio = 1.72, 95% confidence interval: 1.12, 2.44), yet that breastfeeding for more than 6 months conferred a protective effect. Unfortunately, the questionnaire used in our study did not discern between dietary supplements and true vitamin supplementation, nor did we collect information on the specific composition or intended uses of the vitamin supplement reported. As such, we cannot speculate on an association between vitamin D supplementation and childhood leukemia from our study findings.
Furthermore, despite current clinical recommendations (6, 7), our study found that not all infants who were exclusively breastfed received vitamin D supplementation. In fact, 29% of infants who were exclusively breastfed had no reported vitamin intake, and further analysis of this group showed a significant positive association between childhood leukemia and vitamin supplementation (odds ratio = 1.76, 95% confidence interval: 1.15, 2.69). We emphasize that results from a single study should not influence recommendations for public health practice. Rather, future studies are required to replicate our findings and to explore the risk of childhood leukemia associated with specific types of vitamin and mineral supplements, including vitamin D supplementation among breastfed infants, with regard to their composition, bioavailability, and frequency and duration of use.
In summation, our results alone do not warrant changes to current health recommendations for vitamin supplementation among infants and children. We agree that the terminology used to describe vitamin supplementation is variable and that such a distinction is important. Unfortunately, we cannot provide further clarification on the type or composition of vitamin supplements reported among subjects in our study because of the nature of the questionnaire, and the potential for exposure misclassification remains. Therefore, our findings should be interpreted with regard to these limitations. Finally, because of the novelty of our findings, future studies are warranted that would assess risk of childhood leukemia in relation to early-life consumption of a variety of multivitamin-multimineral supplements, as well as other dietary supplements.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Hanauer D, Choi S. Re: "Risk of childhood leukemia associated with vaccination, infection, and medication use in childhood: the Cross-Canada Childhood Leukemia Study" [letter]. Am J Epidemiol (2008) 168(00):000–00.
- MacArthur AC, McBride ML, Spinelli JJ, et al. Risk of childhood leukemia associated with vaccination, infection, and medication use in childhood: the Cross-Canada Childhood Leukemia Study. Am J Epidemiol (2008) 167(5):598–606.
[Abstract/Free Full Text] - Yetley EA. Multivitamin and multimineral dietary supplements: definitions, characterization, bioavailability, and drug interactions. Am J Clin Nutr. (2007) 85(1):269S–276S.
[Abstract/Free Full Text] - Mark JD, Grant KL, Barton LL. The use of dietary supplements in pediatrics: a study of echinacea. Clin Pediatr (Phila) (2001) 40(5):265–269.
[Abstract/Free Full Text] - Goh YI, Bollano E, Einarson TR, et al. Prenatal multivitamin supplementation and rates of pediatric cancers: a meta-analysis. Clin Pharmacol Ther (2007) 81(5):685–691.[CrossRef][Web of Science][Medline]
- Gartner LM, Greer FR. Prevention of rickets and vitamin D deficiency: new guidelines for vitamin D intake. Pediatrics (2003) 111((4 pt 1)):908–910.
[Abstract/Free Full Text] - Canadian Pediatric Society. Vitamin D supplementation: recommendations for Canadian mothers and infants. Paediatr Child Health (2007) 12(7):583–589.
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