Cumulative lead exposure and cognitive performance among the elderly in Johannesburg, South Africa

• First study in LMICs, filling a gap in global Pb exposure research • 55% of elderly participants showed mild cognitive impairment (EDQ ≥ 8) • Higher bone Pb linked to impaired working memory and increased impulsivity Lead (Pb) is a known neurotoxin, but evidence linking low chronic exposure to cognitive performance, particularly in low- and middle-income countries, remains limited. This study examined cumulative bone lead exposure and cognitive performance in older adults living in care facilities located near mines and mine tailings in Gauteng Province, South Africa. We included 139 participants aged 60 to 80 years from state-owned elderly assisted living facilities in City of Johannesburg Municipality, Gauteng. Cumulative lead exposure was measured in the tibia using K-X-ray fluorescence (KXRF). Cognitive performance was assessed using the Early Dementia Questionnaire (EDQ) and the Cambridge Neuropsychological Test Automated Battery (CANTAB), focusing on memory, executive function, attention and psychomotor speed. We examined associations between cumulative bone lead levels and cognitive outcomes using multiple regression models, including quadratic terms to test for nonlinearity. Models were adjusted for age, sex, education, and smoking status. Participants had a mean age of 69.9 years (54% male); 30% reported occupational lead exposure or had been engaged in lead-related activities. Mean bone lead levels were 8.1 µg/g (SD 6.4), and 55% of participants met criteria for mild cognitive impairment (EDQ ≥ 8). Higher cumulative bone lead levels were associated with poorer cognitive performance: each unit increase in bone lead was associated with a 10% higher rate in reaction time (RTI) (adjusted IRR = 1.10; 95% CI: 1.03–1.16). A significant bone lead-sex interaction was observed (p = 0.03), with a stronger association in women (IRR = 1.11, 95% CI: 1.03–1.19) than in men (IRR = 1.05, 95% CI: 1.00–1.10), suggesting potential sex-specific effects. A nonlinear association was observed between bone lead and spatial working memory (SWM) errors (β = 0.022, 95% CI 0.013-0.032), with task errors increasing disproportionately at higher lead levels, indicating worse cognitive performance of memory-related tasks with increasing exposure. This exploratory study suggests low-level cumulative Pb exposure may be associated with poorer cognitive function in the elderly, particularly affecting executive function and impulse control. Larger studies are needed to confirm these associations.