Dementia is the leading cause of dependence and disability in the elderly population worldwide.^1,2 As the mean life expectancy increases, the prevalence of dementia³ and associated monetary costs are expected to increase exponentially.⁴ The pathogenesis of Alzheimer disease is highly complex and likely to be multifactorial, including deregulated amyloid-β, phosphorylated τ, and glycogen synthase kinase 3, as well as inflammation, mitochondrial dysfunction, and calcium dyshomeostasis, suggesting that combination therapy or multitarget drugs might be effective.⁵ Lithium is a multitarget drug that seems to possess neuroprotective abilities by modulating a large array of intracellular cascades and pathways involved in oxidative stress, inflammation, mitochondrial dysfunction, membrane homeostasis, and inhibitory effects on glycogen synthase kinase 3.^5-8 Animal studies^9,10 have found that long-term lithium treatment improves learning and memory, and human observational studies^11,12 suggest that continued treatment with lithium may reduce the risk of dementia among patients with bipolar disorder. In bipolar disorder, treatment with lithium in usual therapeutic daily doses (600-2400 mg) for mood stabilization increases the risk of chronic kidney disease in the elderly population.¹³ In accordance with this finding, lower doses have been used in trials investigating the effects of lithium on cognition among older individuals.^14,15 A placebo-controlled, randomized 2-year trial suggested that long-term treatment with daily low-milligram doses of lithium (150-600 mg) may decrease the rate of developing Alzheimer disease and cerebrospinal fluid concentrations of phosphorylated τ among individuals with mild cognitive impairment.¹⁴ Furthermore, in a 15-month, placebo-controlled randomized clinical trial, a microdose of 300 µg/d of lithium stabilized cognitive impairment in patients with Alzheimer disease.¹⁵ We investigated whether the incidence of dementia in the general population covaries with long-term exposure to microlevels of lithium in drinking water, hypothesizing that higher long-term lithium exposure may be associated with a lower incidence of dementia.

We describe for the first time a current indigenous soil management system in West Africa, in which targeted waste deposition transforms highly weathered, nutrient‐ and carbon‐poor tropical soils into enduringly fertile, carbon‐rich black soils, hereafter “African Dark Earths” (AfDE). In comparisons between AfDE and adjacent soils (AS), AfDE store 200–300% more organic carbon and contain 2–26 times greater pyrogenic carbon (PyC). PyC persists much longer in soil as compared with other types of organic carbon, making it important for long‐term carbon storage and soil fertility. In contrast with the nutrient‐poor and strongly acidic (pH 4.3–5.3) AS, AfDE exhibit slightly acidic (pH 5.6–6.4) conditions ideal for plant growth, 1.4–3.6 times greater cation exchange capacity, and 1.3–2.2 and 5–270 times more plant‐available nitrogen and phosphorus, respectively. Anthropological investigations reveal that AfDE make a disproportionately large contribution (24%) to total farm household income despite its limited spatial extent. Radiocarbon (¹⁴C) aging of PyC indicates the recent development of these soils (115–692 years before present). AfDE provide a model for improving the fertility of highly degraded soils in an environmentally and socially appropriate way, in resource‐poor and food‐insecure regions of the world. The method is also “climate‐smart”, as these soils sequester carbon and enhance the climate‐change mitigation potential of carbon‐poor tropical soils.