Differences in vitamin D status may account for unexplained disparities in cancer survival rates between African and White Americans
Dermato Endocinology Volume 4, Issue 2 April/May/June 2012
Authors: William B. Grant and Alan N. Peiris
- Possible role of serum 25-hydroxyvitamin D in Black–White health disparities in the United States 2010
- Low UVB is associated with 15 types of Cancer – Jan 2012
- Dr. Grant on vitamin D and mortality in VitaminDWiki
- Blacks are more obese, have lower Vitamin D, and have more Cancer etc. than whites – Feb 2018
Considerable disparities in cancer survival rates exist between African Americans (Aas) and white Americans (Was). Various factors such as differences in socioeconomic status (SES), cancer stage at time of diagnosis, and treatment—which this analysis considers primary explanatory factors—have accounted for many of these differences. An additional factor not usually considered is vitamin D. Previous studies have inversely correlated higher solar UV-B (UVB) doses and serum 25-hydroxyvitamin D (25(OH)D) concentrations with incidence and/or mortality rates for about 20 types of cancer and improved survival rates for eight types of cancer. Because of darker skin pigmentation, Aas have 40% lower serum 25(OH)D concentrations than Was. This study reviews the literature on disparities in cancer survival between Aas and Was. The journal literature indicates that there are disparities for 13 types of cancer after consideration of SES, stage at diagnosis and treatment: bladder, breast, colon, endometrial, lung, ovarian, pancreatic, prostate, rectal, testicular, and vaginal cancer; Hodgkin’s lymphoma; and melanoma. Solar UVB doses and/or serum 25(OH)D concentrations have been reported inversely correlated with incidence and/or mortality rates for all of these cancers. This finding suggests that future studies should consider serum 25(OH)D concentrations in addressing cancer survival disparities through both measurements of serum 25(OH)D concentrations and increasing serum 25(OH)D concentrations of those diagnosed with cancer, leading to improved survival rates and reduced disparities.
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The journal literature indicates that there are disparities for 13 types of cancer after consideration of socioeconomic status, stage at diagnosis and treatment: bladder, breast, colon, endometrial, lung, ovarian, pancreatic, prostate, rectal, testicular, and vaginal cancer; Hodgkin’s lymphoma; and melanoma. Solar UVB doses and/or vitamin D have been reported inversely correlated with incidence and/or mortality rates for all of these cancers.The unexplained portion is generally between zero and 30%, with an average near 15%. A disparity of 25% is expected from a consideration of serum vitamin D concentrations for African-Americans (16 ng/ml or 40 nmol/l) and white-Americans (25 ng/ml or 63 nmol/l) based on relations between serum vitamin D concentrations and incidence rates for breast and colorectal cancer. However, the effect for other cancers may be lower than for breast and colorectal cancer.
African-Americans have vitamin D concentrations lower than white-Americans since their darker skin pigmentation reduces the penetration of UVB, thus, reduces the production of vitamin D. Dark skin is an advantage in Africa, where solar UVB doses are quite high, but a disadvantage in the United States, where it isn’t.
According to William B. Grant, Ph.D., a coauthor of the paper and director of Sunlight, Nutrition and Health Research Center, “Raising vitamin D concentrations to 40 ng/ml by taking 1000-4000 IU/d vitamin D3 supplements is the easiest thing African-Americans can do to reduce the heavy burden of cancer they experience. In addition to reducing the risk of cancer, vitamin D would also reduce the risk of cardiovascular disease, diabetes mellitus, respiratory infections and many other chronic and infectious diseases.”
According to Alan N. Peiris, M.D,PhD. FRCP(Lon), a co-author and Chief of Endocrinology at Mountain Home VAMC and East Tennessee State University, monitoring of vitamin D status is often inadequate. Given the wide range of dose responses to vitamin D replacement, it is prudent to monitor levels of 25(OH)D following initiation of dosing. This enables maintaining desired levels over the long term which may facilitate accrual of maximal benefit.
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Considerable disparities in cancer survival rates exist between African Americans (AAs) and white Americans (WAs). Various factors such as socioeconomic status (SES),1 cancer stage at time of diagnosis, and treatment2 have accounted for many of these disparities. Educational attainment is often used as a proxy for SES.3 Other factors include insurance status,4 social determinants in general,5,6 and genetics.7,8 However, even when analyses of cancer survival data include all known or suspected factors affecting survival, AAs still tend to have a lower survival rate than that of WAs, possibly because of unmodeled factors such as biological differences, and perhaps as a consequence of educational level and access to health care as several authors have noted.9-12
Discussions of cancer survival disparities generally overlook the role of vitamin D. For 2001–2004, AAs older than 60 y had a population mean serum 25-hydroxyvitamin D [25(OH)D] concentration of 17 ng/ml compared with 25 ng/ml for WAs.13 Prevalence of hypovitaminosis D [(25(OH)D < 15 ng/ml] in the South was 45% among blacks and 11% among whites.14 In patients participating in a randomized controlled trial of chemotherapy, serum 25(OH)D concentrations were lower in black patients than in white patients and patients of other race (median, 10.7 vs 21.1 vs 19.3 ng/ml, respectively; p < 0.001), as well as in females compared with males (median, 18.3 vs 21.7 ng/ml, respectively; p = 0.0005).15 Solar UV-B (UVB) irradiance is the primary source of vitamin D for most Americans, accounting for 80–90% of vitamin D.16 AAs, with darker skin, are less efficient at producing vitamin D from UVB irradiance.17 In addition, AAs are less likely to have as much vitamin D from oral intake.18
A large body of literature supports a beneficial effect of vitamin D in reducing the risk of cancer incidence and mortality rates. The UVB–vitamin D–cancer hypothesis was proposed in 1980.19 Many ecological studies20-24 have supported this hypothesis, as have observational studies of breast and colorectal cancer.25,26 Two ecological studies found stronger inverse correlations between solar UVB doses and cancer mortality rates than incidence rates.23,24 Several reviews of the UVB-vitamin D-cancer hypothesis have also been published.27,28 Two randomized controlled trials found positive effects.29,30
The dose–response relation for vitamin D has been derived from observational studies for breast and colorectal cancer.25 For the differences in population mean serum 25(OH)D concentrations for 2001–2004,13 the dose–response relations for breast and colorectal cancer indicate a 20–25% increase in incidence rate. The values for cancer incidence are not necessarily the same for cancer survival, but they do suggest the magnitude of the effect. This vitamin D-cancer dose–response relation might underestimate the effect of lower serum 25(OH)D concentrations for AAs since 20% of the black population is older than 60 y, in contrast to only 6% of whites; also, the risk of cancer increases more rapidly for changes of serum 25(OH)D concentration at lower concentrations.
A recent paper addressed vitamin D’s role in explaining some of the cancer survival disparities. Data from the Third National Health and Nutrition Examination Survey (NHANES III) were used to investigate the role of racial disparity from colorectal cancer; adding vitamin D deficiency to the model attenuated the mortality risk associated with being black by a statistically significant 40%.31 Grant and Peiris32 investigated vitamin D’s role in explaining disease disparities between AAs and WAs in general.
This paper surveys the literature on cancer disparities for AAs and WAs as well as the literature on epidemiological studies on vitamin D and cancer to see whether differences in serum 25(OH)D concentrations might explain many of the otherwise-unaccounted-for residual disparities.
Table 1 presents the findings regarding cancer survival with respect to serum 25(OH)D concentrations at the time of diagnosis. Significant inverse correlations between 25(OH)D and cancer survival were found for all-cancer, breast, colon, colorectal, lung, prostate cancer, chronic lymphocytic leukemia/chronic lyphocytic lymphoma, Hodgkin’s lymphoma, and non-Hodgkin’s lymphoma. Studies also reported no significant correlation between serum 25(OH)D and survival for bladder, lung, and ovarian cancer.