Salt use patterns and heavy metal urinary excretion

Overview

Zhang and colleagues analysed NHANES 2003-2018 survey and laboratory data to test whether salt-use patterns were associated with urinary Ba, cadmium (Cd), Co, Cs, Mo, lead (Pb), Sb, Tl, W, and total arsenic (As). This is lane a4 biomonitoring and dietary-exposure evidence, not a salt occurrence study, because the paper does not measure metals in table salt or salt substitutes. The main adjusted signals were higher urinary Mo among salt-substitute users, higher urinary Cd, Pb, and Sb with very frequent table-salt addition, and higher urinary Ba, Cs, Pb, and Tl with cooking/preparation salt use.

Key numbers

• Study population: 11,574 NHANES participants aged 20 years and older, selected from eight consecutive cycles between 2003 and 2018.
• Exclusions before the final analytic sample: participants under 20 years old N = 35,522; missing urinary metal data N = 30,871; missing salt-use pattern data N = 1,235; missing covariate data N = 1,110.
• Table-salt categories in Table 1: ordinary salt N = 7,525 (68%); lite salt N = 351 (2.6%); salt substitute N = 178 (1.4%); does not add salt or substitutes N = 3,520 (28%).
• Overall urinary medians (Q1, Q3), in μg/L: Ba 1.28 (0.61, 2.45); Cd 0.21 (0.10, 0.40); Co 0.35 (0.21, 0.56); Cs 4.5 (2.6, 6.9); Mo 38 (20, 67); Pb 0.42 (0.23, 0.75); Sb 0.05 (0.03, 0.09); Tl 0.16 (0.09, 0.25); W 0.06 (0.03, 0.13); As 7 (3, 15).
• Table 1 urinary Cd medians by table-salt category, in μg/L: ordinary salt 0.20 (0.09, 0.39); lite salt 0.20 (0.11, 0.45); salt substitute 0.20 (0.12, 0.42); does not add salt or substitutes 0.22 (0.11, 0.42); p-value 0.021.
• Table 1 urinary Mo medians by table-salt category, in μg/L: ordinary salt 37 (19, 66); lite salt 33 (19, 62); salt substitute 40 (18, 76); does not add salt or substitutes 40 (21, 70); p-value 0.033.
• Table 1 urinary total As medians by table-salt category, in μg/L: ordinary salt 7 (3, 14); lite salt 6 (3, 12); salt substitute 6 (3, 17); does not add salt or substitutes 8 (4, 17); p-value <0.001.
• Adjusted Table 2 salt-type associations, in μg/mg creatinine regression units: salt substitute vs ordinary salt for Mo 0.155 (0.062, 0.247), p = 0.001; does not add salt or substitutes vs ordinary salt for Mo 0.046 (0.014, 0.078), p = 0.006; does not add salt or substitutes vs ordinary salt for As 0.087 (0.031, 0.143), p = 0.003.
• Adjusted Table 3 table-salt-frequency associations, in μg/mg creatinine regression units: very often vs rarely adding salt at the table for Cd 0.086 (0.037, 0.134), p <0.001, trend p 0.002; Mo -0.055 (-0.102, -0.009), p 0.022, trend p 0.014; Pb 0.156 (0.113, 0.199), p <0.001, trend p <0.001; Sb 0.082 (0.036, 0.128), p <0.001, trend p <0.001.
• Adjusted Table 3 occasional vs rare table-salt addition was significant for Sb only among the listed positive findings: Sb 0.046 (0.002, 0.091), p 0.045.
• Adjusted Table 4 cooking/preparation salt associations, in μg/mg creatinine regression units: occasionally vs never for Ba 0.092 (0.009, 0.175), p 0.032; Cs 0.069 (0.024, 0.115), p 0.003; Tl 0.057 (0.003, 0.111), p 0.042.
• Adjusted Table 4 very often vs never cooking/preparation salt associations: Cs 0.108 (0.07, 0.146), p <0.001; Pb 0.075 (0.017, 0.133), p 0.013; Tl 0.083 (0.032, 0.133), p 0.002.
• Adjusted Table 4 trend p-values were significant for Cs <0.001, Mo 0.016, Pb <0.001, Tl 0.002, and As 0.031.
• The paper states that all ten urinary heavy metals had detection rates exceeding 76.19%, with Sb having the lowest detection rate.

Methods (brief)

NHANES spot urine samples were collected at the Mobile Examination Center, processed, and analysed by the Division of Laboratory Sciences, National Center for Environmental Health, CDC, in Atlanta, Georgia. Ba, Cd, Co, Cs, Mo, Pb, Sb, Tl, W, and As were measured by inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS); values below the LOD were replaced by LOD divided by the square root of 2, and urinary creatinine was measured to account for dilution. The weighted regression models adjusted for age, gender, race/ethnicity, educational attainment, smoking status, poverty income ratio, and BMI; sensitivity analyses added antihypertensive medication use, fish and shellfish consumption in the past 30 days, and current-smoker exclusions. The authors identify cross-sectional design, self-reported salt-use patterns, unadjusted geographic coding, some low detection rates, and biomarker limitations as important constraints; urinary As is total As and is not inorganic arsenic.

Implications

Microbiome: The discussion mentions gut microbiota as a hypothetical high-salt-diet mechanism, but the paper does not measure microbiome endpoints.

Related evidence

• Barium
• Cadmium
• Cobalt
• Cesium
• Molybdenum
• Lead
• Antimony
• Thallium
• Arsenic, Total

Update history

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