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  • br Results br This analysis included

    2020-08-18


    3. Results
    This analysis included 708 black and 651 white men recruited from urology clinics in Nashville, TN or Durham, NC. White men were older
    Table 1
    Description of black and white men in study population.
    Black White Pc
    a PSA data were not collected from Duke/Durham VA site. Analysis of these variables is specific to Vanderbilt study subjects (n = 789). b % genetic African Ancestry from analysis of ancestry informative markers, and evaluated as a continuous variable or as quartiles of the % genetic African ancestry distribution within black men.
    c p-value from Wilcoxon rank sum test or chi-square test evaluating differences between black and white men.
    than black men, but black and white men had a similar BMI, weight, and height (Table 1). Self-reported FF-MAS tracked closely with genetic African ancestry markers, with the majority of white men having no evidence of genetic African ancestry. In contrast, median % genetic African ancestry was 80% within black men, with a wide distribution of % genetic African ancestry scores within black men. PSA levels were also higher among black vs. white men within the subset of 789 par-ticipants with PSA data.
    Black men reported statistically significantly lower dietary magne-sium intake than white men, and blood magnesium levels in black men were also statistically significantly lower than in whites (Table 2). Black men also reported less dietary calcium intake, however this did not correspond to lower blood calcium levels compared to white men. Blood magnesium or calcium levels were not significantly correlated with dietary intake estimates (magnesium (diet vs blood): r(black) = −0.07, p = 0.18, r(white) = -0.02, p = 0.58; calcium(diet vs. blood): r(black) = - 0.06, p = 0.31, r(white) = 0.03, p = 0.52). Indeed, the blood Ca/Mg ratio was significantly higher in black men, while the dietary Ca/Mg level was significantly higher in white men.
    Table 2
    Blood levels and reported dietary intake of magnesium and calcium.
    n Black White Pb
    Ca/Mg
    Ca/Mg
    a Food frequency questionnaires completed by 903 study participants with measured blood magnesium (Mg) and calcium (Ca) levels.
    b P: Wilcoxon rank sum test evaluating differences in Mg, Ca, or Ca/Mg between black and white men. 
    Race differences in blood magnesium or calcium levels did not translate to differences in blood magnesium or calcium levels across categories of genetic African ancestry within black men (Table 3). There was marginally significant variation in dietary calcium and magnesium intake linked with % genetic African ancestry within black men, how-ever no trend was evident and the rationale for why % genetic African ancestry would affect dietary intake in one specific category is unclear. There was insufficient variation in % genetic African ancestry in white men to support a comparable analysis within white men.
    There was no evidence that increasing magnesium or calcium in blood was associated significantly with prostate cancer in either black or white men (Table 4). Similarly, dietary magnesium and calcium in-takes were not significantly associated with prostate cancer (Table 5). In contrast, an increasing dietary Ca/Mg ratio was significantly asso-ciated with a lower risk of total prostate cancer and also high-grade prostate cancer risk, but only within black men. Analyses of prostate cancer with blood magnesium, calcium, or Ca/Mg levels or dietary intakes were similar across study centers, and tests for interaction with study center were not statistically significant (Supplemental Tables 1 and 2). We considered a potential detection bias if magnesium or cal-cium affects PSA levels used to screen men for possible prostate cancer. This analysis was limited to the subset of participants recruited at the Vanderbilt study site and with PSA data at diagnosis (Table 1). Pearson correlation coefficients between PSA and diet or blood magnesium, calcium, or Ca/Mg values ranged from 0.04 to 0.01, and all p-values were greater than 0.31.
    4. Discussion
    This study found a small but statistically significant difference in blood magnesium levels related to race, with lower levels in black men compared to white men. In contrast to our analysis of self-described race, there was no significant differences or suggestive trends between blood magnesium levels and increasing genetic African ancestry. Furthermore, we found no evidence that higher magnesium was asso-ciated with lower prostate cancer risk. Similarly, we found no asso-ciation between blood calcium or the Ca/Mg ratio in blood with pros-tate cancer in either black or white men. Dietary estimates of Ca and Mg