Journal of the National Cancer Institute Advance Access originally published online on May 27, 2008
JNCI Journal of the National Cancer Institute 2008 100(11):826; doi:10.1093/jnci/djn040
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© The Author 2008. Published by Oxford University Press.
CORRESPONDENCE |
Re: Prospective Study of Vitamin D and Cancer Mortality in the United States
Affiliation of author: Sunlight, Nutrition, and Health Research Center, San Francisco, CA
Correspondence to: William B. Grant, PhD, Sunlight, Nutrition, and Health Research Center, PO Box 641603, San Francisco, CA 94164-1603 (e-mail: wbgrant{at}infionline.net).
The study by Freedman et al. (1) found some association of increased vitamin D level with reduced risk of mortality from some cancers, for example, colorectal cancer and breast cancer, but did not find an association with all-cancer mortality rates. The reasons for not finding this expected benefit (2,3) may relate to limitations inherent in the study such as use of a single measurement of serum 25-hydroxyvitamin D (calcidiol) and measurement only in winter in southern latitudes and only in summer in northern ones.
The question addressed in this correspondence is the reliability of different indices for vitamin D in observational studies of cancer incidence and mortality rates. The commonly used indices include prediagnostic serum calcidiol (1), solar ultraviolet-B (UV-B) dose (2,3), latitude, and incidence or mortality rates from nonmelanoma skin cancer. Each has its strengths and weaknesses. Prediagnostic serum calcidiol is easily measured but has the disadvantages that it is generally a single measurement, that it is often measured 5–20 years before cancer outcome, and that it may be correlated with other cancer risk–modifying factors such as dietary components and UV-induced immunosuppression (William B. Grant, PhD, unpublished data, 2007). Solar UV-B dose, obtained from large-scale maps of annual or summertime UV-B at the earth's surface, has been used in several studies (2,3). An advantage of this approach is that the values apply to many years; the disadvantages are that those who migrate may change the outcome (3) and that it is not clear that UV-B irradiance is highly correlated with UV-B dose, especially in older populations. Latitude is an index that is related to solar UV-B dose. An index that is more directly related to integrated lifetime solar UV-B irradiance is nonmelanoma skin cancer incidence or mortality rate. Use of this index was explored recently, and it was found that smoking prevalence by the population also had to be considered (4). Another recent study found diagnosis of nonmelanoma skin cancer to be statistically significantly and inversely correlated with incidence of other solid tumors in sunny countries (5) but directly correlated in less sunny countries. In less sunny countries, less surface area is exposed to the sun unless people travel to sunny vacation spots, so vitamin D production is less than in sunny ones. Another index is a direct estimate of sun exposure by those studied. This index has been used in studies that assessed the risk of breast and prostate cancer and found statistically significant inverse correlations between sun exposure and risk (6,7).
Thus, the results in the article by Freedman et al. (1) should be considered in the context of a growing body of scientific literature that indicates that vitamin D from solar UV-B or oral intake is generally inversely correlated with cancer incidence or mortality rates. For some cancers, such as liver cancer, no benefit of UV-B or vitamin D has been observed (2,3). For others, such as lung cancer, the effect of smoking likely outweighs the beneficial effect of vitamin D in terms of long-term survival.
Funding
UV Foundation, McLean, VA (to W.B.G.); Vitamin D Society, Canada (to W.B.G.); European Sunlight Association (to W.B.G.).
REFERENCES
1. Freedman DM, Looker AC, Chang SC, Graubard BI. Prospective study of serum vitamin D and cancer mortality in the United States. J Natl Cancer Inst (2007) 99(21):1594–1602.
2. Grant WB, Garland CF. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res. (2006) 26(4A):2687–2699.
3. Boscoe FP, Schymura MJ. Solar ultraviolet-B exposure and cancer incidence and mortality in the United States, 1993–2000. BMC Cancer (2006) 6:264.[CrossRef][Medline]
4. Grant WB. A meta-analysis of second cancers after a diagnosis of nonmelanoma skin cancer: additional evidence that solar ultraviolet-B irradiance reduces the risk of internal cancers. J Steroid Biochem Mol. (2007) 103(3–5):668–674.[CrossRef]
5. Tuohimaa P, Pukkala E, Scelo G, et al. Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers: vitamin D as a possible explanation. Eur J Cancer (2007) 43(11):1701–1712.[CrossRef][Web of Science][Medline]
6. John EM, Koo J, Schwartz GG. Sun exposure and prostate cancer risk: evidence for a protective effect of early-life exposure. Cancer Epidemiol Biomarkers Prev (2007) 16(6):1283–1286.
7. John EM, Schwartz GG, Koo J, Wang W, Ingles SA. Sun exposure, vitamin D receptor gene polymorphisms, and breast cancer risk in a multiethnic population. Am J Epidemiol (2007) 166(12):1409–1419.
Response to this Correspondence
CiteULike 
Connotea 
Del.icio.us What's this?
J Natl Cancer Inst 2008 100: 827-828.
This article has been cited by other articles:
|
|
 |
|
  F. R. Perez-Lopez, P. Chedraui, and J. Haya Review Article: Vitamin D Acquisition and Breast Cancer Risk Reproductive Sciences, January 1, 2009; 16(1): 7 - 19. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||