Abstract
Bone is a major storage site as well as an endogenous source of lead in the human body. Dietary sodium and potassium intake may play a role in the mobilization of lead from bone to the circulation. We examined whether association between bone lead and urinary lead, a marker of mobilized lead in plasma, was modified by dietary intake of sodium and potassium among 318 men, aged 48–93 years, in the Veterans Affairs (VA) Normative Aging Study. Dietary sodium and potassium were assessed by flame photometry using 24-h urine samples, and a sodium-to-potassium ratio was calculated from the resulting measures. Patella and tibia bone lead concentrations were measured by K-shell-x-ray fluorescence. Urinary lead was measured by inductively coupled plasma mass spectroscopy in 24-h urine samples. Linear regression models were used to regress creatinine clearance-corrected urinary lead on bone lead, testing multiplicative interactions with tertiles of sodium, potassium, and sodium-to-potassium ratio, separately. After adjustment for age, body mass index, smoking, vitamin C intake, calcium, and total energy intake, participants in the highest tertile of sodium-to-potassium ratio showed 28.1% (95% CI: 12.5%, 45.9%) greater urinary lead per doubling increase in patella lead, whereas those in the second and lowest tertiles had 13.8% (95% CI: −1.7%, 31.7%) and 5.5% (95% CI: −8.0%, 21.0%) greater urinary lead, respectively (p-for-interaction = 0.04). No statistically significant effect modification by either sodium or potassium intake alone was observed. These findings suggest that relatively high intake of sodium relative to potassium may play an important role in the mobilization of lead from bone into the circulation.
Highlights
Lead toxicity is a prevalent and persistent public health problem
In light of previous evidence from the Normative Aging Study (NAS) cohort suggesting that bone resorption significantly modifies release of lead from bone [15], we further examined whether the influence of dietary sodium and potassium intake on bone lead resorption could be through its impact on the bone resorption rate by additional adjustment for multiplicative interaction terms between urinary NTx concentration and bone lead in all regression models
Our findings suggest that a high intake of sodium relative to potassium may increase bone lead resorption among the middle-aged to older men
Summary
Lead toxicity is a prevalent and persistent public health problem. People have been commonly exposed to lead through various routes including air, dust, paint, water, and food [1]. The public health importance of lead toxicity has attracted intense interest, due to large-scale lead exposure events such as in Flint, Michigan, with poisoning due to lead in the water. This has taken place in more than 3000 U.S neighborhoods, with lead poisoning rates in some even greater than those seen in Flint [2]. For the other exposure routes, primary prevention strategies such as removal of lead from gasoline and elimination of lead solder from food and beverage cans have reduced environmental sources of lead remarkably [3]. Low-to-moderate chronic exposure to lead has been associated with age related conditions such as cognitive decline, hearing loss, kidney failure, and cardiovascular disease [5,6,7,8]
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