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Pre-Diagnostic Circulating Vitamin D and Risk of Melanoma in Men

  • Jacqueline M. Major ,

    Contributed equally to this work with: Jacqueline M. Major, Christine Kiruthu

    jacqueline.major@nih.gov

    Affiliation Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America

  • Christine Kiruthu ,

    Contributed equally to this work with: Jacqueline M. Major, Christine Kiruthu

    Affiliation Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America

  • Stephanie J. Weinstein,

    Affiliation Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America

  • Ronald L. Horst,

    Affiliation Heartland Assays, Inc., Ames, Iowa, United States of America

  • Kirk Snyder,

    Affiliation Information Management Services, Inc., Silver Spring, Maryland, United States of America

  • Jarmo Virtamo,

    Affiliation Department of Chronic Disease Prevention, National Institute for Health and Welfare, Helsinki, Finland

  • Demetrius Albanes

    Affiliation Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America

Pre-Diagnostic Circulating Vitamin D and Risk of Melanoma in Men

  • Jacqueline M. Major, 
  • Christine Kiruthu, 
  • Stephanie J. Weinstein, 
  • Ronald L. Horst, 
  • Kirk Snyder, 
  • Jarmo Virtamo, 
  • Demetrius Albanes
PLOS
x

Abstract

Purpose

Various studies have examined the association between serum vitamin D levels and different cancers; however, this is the first prospective study of this association with melanoma risk. The aim of this study is to investigate the association between serum vitamin D [25(OH)D] levels and melanoma in a cohort of older, middle-aged Finnish male smokers.

Methods

We conducted a nested case-control study within the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) Study. From the ATBC cohort, 368 subjects were chosen for our study; 92 participants that developed melanoma and 276 matched control subjects. At study baseline, lifestyle questionnaires and blood samples were collected. Serum 25(OH)D was modeled as three sets of categorical variables: clinically-defined categories, season-specific quartiles and season-adjusted residual quartiles. Conditional logistic regression was used to obtain odds ratios (ORs) and 95% confidence intervals (95% CIs) to estimate the association between circulating vitamin D and melanoma risk.

Results

Overall no association of serum 25(OH)D and melanoma risk was observed. A decreased risk of developing melanoma was observed in the middle categories compared to the lowest category, albeit not significant.

Conclusion

Results indicate no association between serum 25(OH)D levels and melanoma. Additional studies, including possibly consortium efforts, are needed to investigate the association between serum 25(OH)D levels and risk of melanoma in larger, more diverse study populations.

Introduction

Skin cancer is the most common cancer in the United States, with malignant melanoma being the most lethal and clinically invasive form resulting from transformation of melanocytes in skin (ocular and intestinal primaries also occur) [1]. The incidence of melanoma has more than doubled in the past 20 years, and among men, it is the fifth most common cancer in the U.S. [2]. Risk of developing melanoma increases with age and is higher among men and fair-skinned individuals; one in 39 Caucasian men develops melanoma in their lifetime. The primary etiologic factor for melanoma is solar ultraviolet (UV) radiation exposure [3][5], but interest in the potential role of circulating high vitamin D concentrations has increased owing in part to recently observed associations with reduced melanoma tumor progression and improved survival [6][8].

Vitamin D status is contributed to by ultraviolet B (UVB) exposure from sunlight and by diet and supplements [9], [10]. Vitamin D is first metabolized in the liver to 25-hydroxyvitamin D [25(OH)D], and then in the kidney and other organs to its active form, 1,25-dihydroxycholecalciferol [1,25(OH)D]. 1,25(OH)D is essential to calcium homeostasis and functions by regulating cell proliferation and differentiation in various organs [11]. Circulating levels of 25(OH)D serves as a marker of vitamin D status based on its accessibility and precursor function to hormonal form, 1,25(OH)D [12], [13]. Although some prospective studies suggest that high levels of circulating 25(OH)D may be associated with decreased risk of colorectal cancer, and possibly breast cancer [9], the relation with incident melanoma is unclear. In human melanoma cell lines, in vitro studies indicate 1,25(OH)D inhibits cell growth [14], [15]. Case-control studies have found associations with improved prognosis, but no association between 25(OH)D and disease status based on post-diagnostic blood samples [6], [16]. There is a need, therefore, to further examine this relation in prospective studies in which serum vitamin D levels were measured prior to disease development. The purpose of this study was to examine the association between prediagnostic serum vitamin D [25(OH)D] and subsequent risk of melanoma in a prospective study of older, middle-aged Finnish men.

Materials and Methods

Study population

We conducted a nested case-control study within the Alpha-Tocopherol, Beta Carotene Cancer Prevention (ATBC) Study cohort. The present analysis included 368 men; 92 participants that developed melanoma and 276 matched (3∶1 ratio) control subjects to provide sufficient power to detect an odds ratio of 0.50 at 80% power (alpha = 0.05). Incident cases, as defined by the International Classification of Diseases 9 code (172, melanoma), were diagnosed from April 1986 through April 2005. All melanoma cases were identified through the Finnish Cancer Registry, which provides close to 100% population-based cancer ascertainment in Finland. Controls were selected from ATBC Study participants that were alive at the time of the case diagnoses, and were matched to each case based on age (+/−3 years) and date of baseline serum collection (+/−30 days).

The ATBC Study was a randomized, controlled trial that examined whether supplementation with alpha-tocopherol (vitamin E) or beta-carotene would reduce the cancer incidence in male smokers. Details have been previously reported [17], but in brief, the study was conducted in southwestern Finland and included 29,133 male smokers between the ages of 50–69 years, who smoked at least five cigarettes a day, had no recent history of cancer, severe illnesses (e.g., cirrhosis of liver, chronic renal insufficiency, or other medical problems), or use of predefined doses of vitamin E, A or beta carotene. The study was reviewed and approved by the institutional review boards of the National Public Health Institute in Finland and the U.S. National Cancer Institute. All study participants provided written informed consent.

Study measures

At study entry, investigators administered questionnaires that collected information on medical history and lifestyle behaviors, including diet and smoking history. Height and weight were measured using standard methods, and body mass index (BMI, kg/m2) was calculated. A follow-up questionnaire was administered 3 years after baseline which ascertained information on skin behavior (e.g., more prone to sunburn) and sun exposure.

Laboratory assays.

Serum was collected at study entry, stored at −70°C, and 25(OH)D levels were analyzed using the LIAISON 25-OH Vitamin D Total Assay (DiaSorin, Inc., Stillwater, MN) at Heartland Assays, Inc. (Iowa). Matched case and control samples were masked to case status and assayed in batches. Quality control samples were 5% of the total number of samples. Intrabatch and interbatch coefficients of variation (CV) ranged between 9.3%–11.0% and 12.3%–13.6%, respectively.

Statistical analysis

Descriptive statistics were calculated for baseline characteristics of participants by cancer status. The distribution of baseline characteristics between cases and controls were compared using the Wilcoxon rank-sum test for continuous variables and Chi-square test for categorical variables.

Serum 25 (OH)D was modeled as three distinct categorical variables: clinically-defined categories (<25, 25 to 37.49, 37.50 to 49.99 and 50+ nmol/L), season-specific quartiles, and quartiles of season-adjusted residuals. The season-specific quartiles of 25 (OH)D were based on the distribution among control subjects within the “darker” (November–April) and “lighter” (May–October) months. The quartiles for the residuals of the season-adjusted 25(OH)D values were obtained using a weighted polynomial regression and modeling on log-transformed 25(OH)D levels that adjusted for date of blood draw [18]. Conditional logistic regression was used to obtain odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to estimate the association between vitamin D levels and melanoma risk. Potential confounders and variables associated with 25(OH)D levels and/or melanoma were included in the initial model building process. Variables that changed the ORs by 10% or more were considered as potential confounders. Final parsimonious models adjusted for age (continuous), date of serum collection, skin behavior (burns easily: no/yes/missing), dietary cholesterol (continuous), height (continuous), and weight (continuous). Effect modification of cigarette smoking, BMI, height, leisure physical activity, or trial supplementation was examined through inclusion of a cross-product term in the model. Data were analyzed using SAS® (version 9.2, SAS Institute Inc., Cary, NC) and all P-values were two-sided.

Results

Melanoma cases were taller, heavier, and more likely to have at least an elementary school education than the controls (Table 1). By contrast, cases had lower dietary intake of cholesterol and fish and were less likely to have reported their skin type and whether or not they had taken trips to the south. Serum 25(OH)D levels were similar for cases and controls. The median age at diagnosis was 65 years; mean (standard deviation) was 66 (7.1) years. The median time from baseline blood draw to diagnosis was 8.9 years. The median follow-up time for the control subjects was 18.2 years.

We observed no association between serum 25(OH)D levels and risk of melanoma (Table 2; Ptrends>0.05). For clinically-defined categories, lower risk of melanoma was suggested for serum vitamin D levels between 37.50 to 49.99 nmol/L, but then an increased risk of melanoma for men whose vitamin D levels were ≥50 nmol/L (ORs = 0.60 and 1.32, with corresponding 95% CIs = 0.25–1.44 and 0.64–2.72, respectively) when compared to men whose prediagnostic levels were <25 nmol/L. Similarly, season-specific quartiles showed a decreased risk of melanoma in the second quartile (OR = 0.79; 95% CI = 0.34–1.81) and an increased risk in the third quartile (OR = 1.33; 95% CI = 0.62–2.85) when compared to the lowest quartile, albeit not statistically significant. Season-adjusted residuals, however, suggested an increased melanoma risk in the second and third quartiles (ORs = 1.20 and 1.56 with 95% CIs = 0.55–2.64 and 0.74–3.28, respectively). Tests for non-linear trends were not statistically significant (P-values>0.05, data not shown), and there were no significant interactions between circulating vitamin D levels and the number of cigarettes smoked per day, BMI, height, leisure physical activity, or trial supplementation (data not shown).

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Table 2. Adjusted odds ratios of melanoma by categories of serum 25(OH)D levels.

https://doi.org/10.1371/journal.pone.0035112.t002

Discussion

The present study is the first to prospectively examine prediagnostic serum vitamin D concentrations in relation to subsequent risk of melanoma. Our findings indicate no statistically significant association between serum 25(OH)D levels and melanoma, although there was a suggested protective association in the second quartiles compared to the lowest levels.

A previous population study examining vitamin D and non-melanoma skin cancer (NMSC) showed high serum 25(OH)D levels related to decreased risk of NMSC [19], while a case study of 14 melanoma patients found 25(OH)D serum levels ranged from 50 to 125 nmol/L, not supporting the hypothesis that deficient levels are associated with the development of malignant melanoma [20]. Our results are similar to those observed in a case-control study showing median levels of serum 25(OH)D in melanoma patients not significantly different from those of the controls (42 vs. 47 nmol/L; P = 0.44) [16]. That study did, however, find median levels to be significantly lower in patients with advanced melanoma (stage IV, metastasized) than those with stage Ia/b (33 vs. 41 nmol/L; P<0.01). Because we did not have disease stage available, we were unable to examine potential associations between serum vitamin D levels and risk of advanced melanoma in the present analysis. Although previous prospective studies have not examined risk of developing melanoma, associations between serum vitamin D level and cancer risk have been reported, with a potential U-shaped association suggested for prostate and pancreatic cancer [11], [21]. Reports from population-based studies examining higher dietary or supplemental intake of vitamin D have been inconsistent; some showing a reduced risk of melanoma overall [22], [23] and some showing no association [24], [25]. It should be noted, however, that dietary intakes of vitamin D are notoriously difficult to assess and may not reflect accurate vitamin D status.

A strength of our study is having examined serum 25(OH)D and melanoma in a prospective cohort ensuring that our vitamin D measure preceded the development of melanoma by up to 18 years. In addition, cases were identified through the Finnish Cancer Registry with approximately 100% case ascertainment. Controls were matched to the cases by age and month of blood collection, which likely reduced misclassification of vitamin D status due to seasonal variation. A limitation of the study is a lack of generalizability of the findings given that our study population consists of older middle-aged Finnish male smokers; median age at diagnosis was 65 years. We only had a single measure of serum 25(OH)D, however, which may not reflect long-term exposure and did not allow us to examine changes in vitamin D concentration levels over time although moderate correlations between measures collected years apart have been reported elsewhere [26], [27]. The interpretation of the results is limited by the small number of cases (n = 92), which may have made detection of a significant associations difficult. Further, we acknowledge that the Finnish population used in the present analysis are known to have low levels of serum 25(OH)D compared to U.S. study populations for several reasons, including the substantially higher latitude of Finland (60 degrees N), low dietary and minimal supplemental intakes of vitamin D among the ATBC Study participants, and the fact that blood samples were not collected during peak summer vacation times (mid- June through August) because the study clinics were effectively closed. It should be mentioned, however, that there is ongoing debate regarding the definition of “sufficient” levels, with consensus not yet reached. For example, in the recent IOM report, the committee's review of data suggests that persons are at risk of deficiency at serum 25(OH)D levels of below 30 nmol/L. Our cases and controls had median serum values of approximately 32 nmol/L.

In conclusion, prediagnostic circulating vitamin D concentrations were not associated with subsequent risk of melanoma. Additional prospective studies are needed to investigate the association between serum 25(OH) levels and risk of melanoma in study populations that include nonsmokers and women, and ideally, with a larger number of melanoma cases and data for stage at diagnosis.

Author Contributions

Conceived and designed the experiments: DA JMM SJW JV. Analyzed the data: JMM CK. Contributed reagents/materials/analysis tools: SJW KS RLH JV. Wrote the paper: JMM DA CK. Read and approved the final manuscript: JMM CK SJW RLH KS JV DA.

References

  1. 1. Gruber SB, Armstrong BK (2006) Cutaneous and Ocular Melanoma. In: Schottenfeld D, Fraumeni JFJ, editors. Cancer Epidemiology and Prevention. Third ed. New York NY: Oxford University Press. pp. 1196–1229.SB GruberBK Armstrong2006Cutaneous and Ocular Melanoma.D. SchottenfeldJFJ FraumeniCancer Epidemiology and Prevention. Third edNew York NYOxford University Press11961229
  2. 2. American Cancer Society (2009) Cancer Facts and Figures. Atlanta: American Cancer Society. American Cancer Society2009Cancer Facts and FiguresAtlantaAmerican Cancer Society
  3. 3. Elwood JM, Jopson J (1997) Melanoma and sun exposure: an overview of published studies. Int J Cancer 198–203.JM ElwoodJ. Jopson1997Melanoma and sun exposure: an overview of published studies.Int J Cancer198203United States. United States.
  4. 4. Gandini S, Sera F, Cattaruzza MS, Pasquini P, Picconi O, et al. (2005) Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer 45–60.S. GandiniF. SeraMS CattaruzzaP. PasquiniO. Picconi2005Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure.Eur J Cancer4560England. England.
  5. 5. Osterlind A, Tucker MA, Stone BJ, Jensen OM (1988) The Danish case-control study of cutaneous malignant melanoma. II. Importance of UV-light exposure. Int J Cancer 42: 319–324.A. OsterlindMA TuckerBJ StoneOM Jensen1988The Danish case-control study of cutaneous malignant melanoma. II. Importance of UV-light exposure.Int J Cancer42319324
  6. 6. Hutchinson PE, Osborne JE, Pringle JH (2010) Higher serum 25-hydroxy vitamin D3 levels at presentation are associated with improved survival from melanoma, but there is no evidence that later prevailing levels are protective. J Clin Oncol e492–493; author reply 494–495.PE HutchinsonJE OsborneJH Pringle2010Higher serum 25-hydroxy vitamin D3 levels at presentation are associated with improved survival from melanoma, but there is no evidence that later prevailing levels are protective.J Clin Oncole492493; author reply 494–495United States. United States.
  7. 7. Randerson-Moor JA, Taylor JC, Elliott F, Chang YM, Beswick S, et al. (2009) Vitamin D receptor gene polymorphisms, serum 25-hydroxyvitamin D levels, and melanoma: UK case-control comparisons and a meta-analysis of published VDR data. Eur J Cancer 3271–3281.JA Randerson-MoorJC TaylorF. ElliottYM ChangS. Beswick2009Vitamin D receptor gene polymorphisms, serum 25-hydroxyvitamin D levels, and melanoma: UK case-control comparisons and a meta-analysis of published VDR data.Eur J Cancer32713281England. England.
  8. 8. Newton-Bishop JA, Beswick S, Randerson-Moor J, Chang YM, Affleck P, et al. (2009) Serum 25-hydroxyvitamin D3 levels are associated with breslow thickness at presentation and survival from melanoma. J Clin Oncol 27: 5439–5444.JA Newton-BishopS. BeswickJ. Randerson-MoorYM ChangP. Affleck2009Serum 25-hydroxyvitamin D3 levels are associated with breslow thickness at presentation and survival from melanoma.J Clin Oncol2754395444
  9. 9. Holick MF (2007) Vitamin D deficiency. N Engl J Med 357: 266–281.MF Holick2007Vitamin D deficiency.N Engl J Med357266281
  10. 10. Gandini S, Boniol M, Haukka J, Byrnes G, Cox B, et al. (2011) Meta-analysis of observational studies of serum 25-hydroxyvitamin D levels and colorectal, breast and prostate cancer and colorectal adenoma. International journal of cancer Journal international du cancer 128: 1414–1424.S. GandiniM. BoniolJ. HaukkaG. ByrnesB. Cox2011Meta-analysis of observational studies of serum 25-hydroxyvitamin D levels and colorectal, breast and prostate cancer and colorectal adenoma.International journal of cancer Journal international du cancer12814141424
  11. 11. Tuohimaa P, Tenkanen L, Ahonen M, Lumme S, Jellum E, et al. (2004) Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal, nested case-control study in the Nordic countries. Int J Cancer 108: 104–108.P. TuohimaaL. TenkanenM. AhonenS. LummeE. Jellum2004Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal, nested case-control study in the Nordic countries.Int J Cancer108104108
  12. 12. Giovannucci E (2009) Vitamin D and cancer incidence in the Harvard cohorts. Ann Epidemiol 19: 84–88.E. Giovannucci2009Vitamin D and cancer incidence in the Harvard cohorts.Ann Epidemiol198488
  13. 13. Tworoger SS, Lee IM, Buring JE, Rosner B, Hollis BW, et al. (2007) Plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and risk of incident ovarian cancer. Cancer Epidemiol Biomarkers Prev 16: 783–788.SS TworogerIM LeeJE BuringB. RosnerBW Hollis2007Plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and risk of incident ovarian cancer.Cancer Epidemiol Biomarkers Prev16783788
  14. 14. Colston K, Colston MJ, Feldman D (1981) 1,25-dihydroxyvitamin D3 and malignant melanoma: the presence of receptors and inhibition of cell growth in culture. Endocrinology 108: 1083–1086.K. ColstonMJ ColstonD. Feldman19811,25-dihydroxyvitamin D3 and malignant melanoma: the presence of receptors and inhibition of cell growth in culture.Endocrinology10810831086
  15. 15. Evans SR, Houghton AM, Schumaker L, Brenner RV, Buras RR, et al. (1996) Vitamin D receptor and growth inhibition by 1,25-dihydroxyvitamin D3 in human malignant melanoma cell lines. J Surg Res 127–133.SR EvansAM HoughtonL. SchumakerRV BrennerRR Buras1996Vitamin D receptor and growth inhibition by 1,25-dihydroxyvitamin D3 in human malignant melanoma cell lines.J Surg Res127133United States. United States.
  16. 16. Nurnberg B, Graber S, Gartner B, Geisel J, Pfohler C, et al. (2009) Reduced serum 25-hydroxyvitamin D levels in stage IV melanoma patients. Anticancer Res 3669–3674.B. NurnbergS. GraberB. GartnerJ. GeiselC. Pfohler2009Reduced serum 25-hydroxyvitamin D levels in stage IV melanoma patients.Anticancer Res36693674Greece. Greece.
  17. 17. The ATBC Cancer Prevention Study Group (1994) The alpha-tocopherol, beta-carotene lung cancer prevention study: design, methods, participant characteristics, and compliance. The ATBC Cancer Prevention Study Group. Ann Epidemiol 4: 1–10.The ATBC Cancer Prevention Study Group1994The alpha-tocopherol, beta-carotene lung cancer prevention study: design, methods, participant characteristics, and compliance. The ATBC Cancer Prevention Study Group.Ann Epidemiol4110
  18. 18. Gallicchio L, Helzlsouer KJ, Chow WH, Freedman DM, Hankinson SE, et al. (2010) Circulating 25-hydroxyvitamin D and the risk of rarer cancers: Design and methods of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers. Am J Epidemiol 10–20.L. GallicchioKJ HelzlsouerWH ChowDM FreedmanSE Hankinson2010Circulating 25-hydroxyvitamin D and the risk of rarer cancers: Design and methods of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers.Am J Epidemiol1020United States. United States.
  19. 19. Tang JY, Parimi N, Wu A, Boscardin WJ, Shikany JM, et al. (2010) Inverse association between serum 25(OH) vitamin D levels and non-melanoma skin cancer in elderly men. Cancer Causes Control 21: 387–391.JY TangN. ParimiA. WuWJ BoscardinJM Shikany2010Inverse association between serum 25(OH) vitamin D levels and non-melanoma skin cancer in elderly men.Cancer Causes Control21387391
  20. 20. Reichrath J, Querings K (2004) No evidence for reduced 25-hydroxyvitamin D serum level in melanoma patients. Cancer Causes Control 15: 97–98.J. ReichrathK. Querings2004No evidence for reduced 25-hydroxyvitamin D serum level in melanoma patients.Cancer Causes Control159798
  21. 21. Stolzenberg-Solomon RZ, Hayes RB, Horst RL, Anderson KE, Hollis BW, et al. (2009) Serum vitamin D and risk of pancreatic cancer in the prostate, lung, colorectal, and ovarian screening trial. Cancer Res 1439–1447.RZ Stolzenberg-SolomonRB HayesRL HorstKE AndersonBW Hollis2009Serum vitamin D and risk of pancreatic cancer in the prostate, lung, colorectal, and ovarian screening trial.Cancer Res14391447United States. United States.
  22. 22. Millen AE, Tucker MA, Hartge P, Halpern A, Elder DE, et al. (2004) Diet and melanoma in a case-control study. Cancer Epidemiol Biomarkers Prev 1042–1051.AE MillenMA TuckerP. HartgeA. HalpernDE Elder2004Diet and melanoma in a case-control study.Cancer Epidemiol Biomarkers Prev10421051United States. United States.
  23. 23. Vinceti M, Malagoli C, Fiorentini C, Longo C, Crespi CM, et al. (2011) Inverse association between dietary vitamin D and risk of cutaneous melanoma in a northern Italy population. Nutr Cancer 506–513.M. VincetiC. MalagoliC. FiorentiniC. LongoCM Crespi2011Inverse association between dietary vitamin D and risk of cutaneous melanoma in a northern Italy population.Nutr Cancer506513England. England.
  24. 24. Weinstock MA, Stampfer MJ, Lew RA, Willett WC, Sober AJ (1992) Case-control study of melanoma and dietary vitamin D: implications for advocacy of sun protection and sunscreen use. J Invest Dermatol 98: 809–811.MA WeinstockMJ StampferRA LewWC WillettAJ Sober1992Case-control study of melanoma and dietary vitamin D: implications for advocacy of sun protection and sunscreen use.J Invest Dermatol98809811
  25. 25. Tang JY, Fu T, Leblanc E, Manson JE, Feldman D, et al. (2011) Calcium Plus Vitamin D Supplementation and the Risk of Nonmelanoma and Melanoma Skin Cancer: Post Hoc Analyses of the Women's Health Initiative Randomized Controlled Trial. J Clin Oncol 3078–3084.JY TangT. FuE. LeblancJE MansonD. Feldman2011Calcium Plus Vitamin D Supplementation and the Risk of Nonmelanoma and Melanoma Skin Cancer: Post Hoc Analyses of the Women's Health Initiative Randomized Controlled Trial.J Clin Oncol30783084United States. United States.
  26. 26. Hofmann JN, Yu K, Horst RL, Hayes RB, Purdue MP (2010) Long-term variation in serum 25-hydroxyvitamin D concentration among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Cancer Epidemiol Biomarkers Prev 927–931.JN HofmannK. YuRL HorstRB HayesMP Purdue2010Long-term variation in serum 25-hydroxyvitamin D concentration among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.Cancer Epidemiol Biomarkers Prev927931United States. United States.
  27. 27. Jorde R, Sneve M, Hutchinson M, Emaus N, Figenschau Y, et al. (2010) Tracking of serum 25-hydroxyvitamin D levels during 14 years in a population-based study and during 12 months in an intervention study. Am J Epidemiol 903–908.R. JordeM. SneveM. HutchinsonN. EmausY. Figenschau2010Tracking of serum 25-hydroxyvitamin D levels during 14 years in a population-based study and during 12 months in an intervention study.Am J Epidemiol903908United States. United States.