br Introduction br Prostate cancer
Prostate cancer is the leading non-skin cancer and second leading cause of cancer death among men in the U.S . There are substantive diﬀerences in prostate cancer incidence and mortality associated with race, with a 63% higher incidence and a 2.4-fold higher mortality overall among black men compared to white men [2–5], and a shorter time period of disease-free survival . Further understanding poten-tial contributing causes for these race diﬀerences in prostate cancer detection and survival is a priority area in prostate cancer research.
Magnesium deficiency is common, with analyses of data from National Health and Nutrition Examination Survey finding that 79% of U.S. adults have magnesium intake below the Recommended Dietary Allowance (males: 420 mg/d) . Our prior study of predominately
white men found that lower blood magnesium levels were associated with an increased risk of high-grade prostate cancer . We also re-ported that the subset of black men in that study had lower blood magnesium levels than white men (2.03 vs. 2.16 ng/ml, respectively,
Calcium has long held an interest in cancer progression with po-tential roles as an essential messenger regulating SPDP proliferation and apoptosis . Prior human studies have reported an increased risk of aggressive prostate cancer associated with higher calcium levels
∗ Corresponding author. 66 North Pauline Drive, Suite 600, Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, TN, 38163, USA.
E-mail addresses: [email protected] (J.H. Fowke), [email protected] (T. Koyama), [email protected] (Q. Dai), [email protected] (S.L. Zheng), [email protected] (J. Xu), [email protected] (L.E. Howard), [email protected] (S.J. Freedland).
, however studies have also reported an increased risk of non-ag-gressive prostate cancer  or a protective association with prostate cancer risk [14,15]. Such inconsistencies may reflect the range and biological complexity of these minerals in the body. Indeed, calcium and magnesium biologically interact through competition for intestinal absorption, transport, and renal reabsorption [16–18], and magnesium deficiency increases calcium retention and activity [19–21]. Further understanding the roles of magnesium in prostate cancer may require inclusion of calcium as one biological element that substantially aﬀects magnesium action and availability.
This case-control analysis investigated the link between magnesium and prostate cancer in black and white men, and also investigated the potential interaction between magnesium and calcium levels. To ad-dress the challenge of magnesium and calcium measurement, our analysis included blood levels of magnesium and calcium as well as dietary intake estimates from food frequency questionnaires. Analysis of genetic markers of African ancestry was used as a complement to self-reported race in the analysis that begins to separate the inherited and non-inherited components of self-reported race. As prior data suggest that black men will have lower magnesium intake and lower blood magnesium levels than white men, we hypothesized that the protective association between magnesium measures and prostate cancer will be stronger within black men compared to white men. Analyses may provide evidence that magnesium deficiency contributes to race diﬀerences in prostate cancer risk, and lead to future in-vestigations of mechanisms of magnesium in prostate cancer or dietary interventions to support the intake of magnesium-rich foods.
2. Materials and methods
Participants came from two separate, but similar pre-existing stu-dies located at Vanderbilt University Medical Center (Nashville, TN, USA) and the Veterans Administrations Hospital in Durham, NC, and Duke University Medical Center. Details of each protocol were pre-viously reported [15,22]. Recruitment for this project targeted men over age 40 years and who were obtaining a diagnostic prostate biopsy. Biospecimen and data collection occurred prior to prostate biopsy, such that patients, medical staﬀ, and research staﬀ had no knowledge of the patient prostate cancer status at time of recruitment and data collec-tion. All recruitment and data collection protocols were approved by the respective IRBs, with additional review from the Department of Defense Human Subjects Research Panel, and all participants provided written informed consent.
Fasting blood was collected from most men at the Durham site, while fasting collection was not feasible from community urology clinics in Nashville. Blood processing and storage were similar under both protocols. Whole blood was refrigerated immediately after col-lection, and serum was processed within 4–6 h of collection, aliquoted into labeled cryovials, and stored at −80 °C. DNA was extracted from blood at institutional genetic core laboratories, quantified, and stored at −80 °C.