Demographic information
In all, 1595 (587 male and 1008 female) participants from twenty villages near Xiaogan were surveyed, and the demographic character was shown (Table 1). The average participant age was 63.89 (±8.4) years old (the female average was 65.01 years old and the male average was 63.24). The UCd concentration was in the scope of 0.030 to 20.279 μg/g cr (Table 1). The maximum geometric mean of the male UCd levels (4.726 μg/g cr) was lower than that of females (5.393 μg/g cr). The average UCd of the total population was estimated to be 4.507 μg/g cr. An increasing trend was shown between male and female UCd levels. The geometric mean value for UCd among females was higher than that for males (p < 0.05). The mean UNAG value among the males (11.790 U/g cr) was different from that for females (11.817 U/g cr). The average male Uβ2-MG level was 611.63 μg/g cr, and the female average was 643.10 μg/g cr (Table 1). The mean UNAG (11.807 U/g cr) for all subjects was lower than the national standard threshold value (17 U/g cr) (p < 0.05) as found by MOHC in 1998, and the Uβ2-MG mean (631.33 μg/g cr) was lower than 1000 μg/g cr (p < 0.05). Further analysis revealed that the maximum value found for UNAG was 3.89 times the national standard threshold value, and the Uβ2-MG value was 2.97 times the standard. There was a large undulation shown in the scope of UNAG, which varied from 0.411 to 66.157 U/g cr, and Uβ2-MG changed from 4.09 to 2965.66 μg/g cr.
The geometric mean for the female UCd level (4.522 μg/g cr) was higher than that for the males (4.483 μg/g cr) (p < 0.05) (Table 2). Per clinical standards, patients are termed at risk if their UCd levels are higher than 5.000 μg/g cr. In our study, the median UCd value for both male or female participants was higher than the national standard threshold value (5 μg/g cr) recommended by GOMOHC in 2010 [31].
Additionally, for high UCd concentration level, more than 5% of male (12.263 μg/g cr) was found lower than of female (13.520 μg/g cr). It was found that the UCd for 53.79% of all participants had high values, meaning that half of the sample was at risk of high Cd exposure. The mean UCd values for those aged 80–90 years old were 2.5 the national threshold standard. The likelihood of high UCd increased with age (p < 0.001) (Table 2). The mean UNAG (22.433 U/g cr) was far above the national threshold value of 17 U/g cr, as was the mean Uβ2-MG (2122.665 μg/g cr) in relation to the national threshold value of 1000 μg/g cr). The 75th to 95th percentiles for UNAG (20.661–33.271 U/g cr) and Uβ2-MG (1176.22–1834.13 μg/g cr) concentrations were likewise high.
Relationship between urinary cadmium burden and renal dysfunction index
Index UNAG and Uβ2-MG were outlined. The percentage of high UNAG among female participants was 32.34%, and among males, it was 26.58% (Table 3). The percentages were higher for Uβ2-MG, with 41.77% for females and 36.63% for males. Thus, a trend of elevated values in UCd levels and the indexes is mentioned above. The rate of abnormal UNAG among males was 53.49%, and that of females was 61.44% (Table 3). The Uβ2-MG values ranged from 17.44% to 67.44% among makes and from 20.41% to 71.90% among. Uβ2-MG was more sensitive than UNAG (p < 0.05), supported previous results that Uβ2-MG might be a more sensitive biomarker than UNAG for Cd exposure risk [32]. Moreover, the odds of UNAG and Uβ2-MG increased linearly with UCd levels (p < 0.01). A further χ2 test of the linear trend verified that the indexes related to UCd levels (p < 0.01). An interesting finding was that the relationship of index response to renal dysfunction in females was higher than in males for the same UCd burden (Table 3).
ales for the same UCd burden (Table 3).
A linear regression indicated a positive correlation between age and UCd (p < 0.05) (Table 4). The correlation coefficient of the Uβ2-MG level was higher than of UNAG (p < 0.05). Furthermore, the positive correlations between UCd and age, gender, UNAG, and Uβ2-MG were validated using Pearson correlation analysis (p < 0.05), but no significant correlation was found for village site (p > 0.05) (Table 4). A positive correlation between UNAG and Uβ2-MG was also confirmed (p < 0.01).
The renal indicators UNAG and Uβ2-MG were considered to be dependent variables, and the age, sex, region, and UCd levels (statistically analyzed after logarithmic transformation obeying the normal distribution) were considered to be independent variables. The variables that were entered into the regression (age, UCd, UNAG, and Uβ2-MG) were subjected to multiple linear regression analyses based on linear regression analysis. Certain factors, such as age, sex, and environmental exposure, may have resulted in a misleading assessment of the relationship between UCd burden and renal indexes. A step-by-step linear regression analysis, found β’ values for UNAG and Uβ2-MG of 0.459 and 0.493, respectively (Table 5). It was also found that UNAG and Uβ2-MG were sensitive biomarkers, and both may serve as primary indexes for BMD calculations.
BMD of UCd for UNAG and Uβ2-MG
The optimized logistic model was selected when fitting UNAG or Uβ2-MG. The BMD of UCd was presented and grouped according to gender (Table 6). The BMR was set at 10%, and UNAG was employed. BMD and BMDL for male UCd were nearly 3.876 U/g cr and 3.486 U/g cr, respectively. For the same parameter, the BMD and BMDL for female UCd were 3.236 U/g cr and 2.998 U/g cr, respectively. Given the same parameters for Uβ2-MG, the BMD and BMDL for male UCd were nearly 2.784 μg/g cr and 2.506 μg/g cr, respectively, and the BMD and BMDL of female UCd were about 2.416 μg/g cr and 2.236 μg/g cr, respectively (Table 6). This indicates that the BMDL of female UCd was lower than that of the male, implying that females were more vulnerable than males for the same UCd burden.
Based on the previous research, more study of the precise indexes was performed. In order to ensure the completeness and representativeness of the experimental results, all the dichotomous models for BMDs were applied, with BMR set as 15%, 20%, 25%, and 30%. The national standard (5 μg/g cr) was produced by setting BMR to 20%. To protect people’s health from high levels of Cd exposure, additional restrictions to the sensitivity index and BMD should be considered.