Abstract:
There are no studies of oral health in relation to esophageal cancer in Africa, or of Eastern Africa’s endemic dental fluorosis, an
irreversible enamel hypo-mineralization due to early-life excessive fluoride intake. During 2014–18, we conducted a case–control
study of squamous cell esophageal cancer in Eldoret, western Kenya. Odds ratios (AORs (95% confidence intervals)) were adjusted
for design factors, tobacco, alcohol, ethnicity, education, oral hygiene and missing/decayed teeth. Esophageal cancer cases
(N = 430) had poorer oral health and hygiene than controls (N = 440). Compared to no dental fluorosis, moderate/severe fluorosis,
which affected 44% of cases, had a crude OR of 20.8 (11.6, 37.4) and on full adjustment was associated with 9.4-fold (4.6, 19.1)
increased risk, whilst mild fluorosis (43% of cases) had an AOR of 2.3 (1.3, 4.0). The prevalence of oral leukoplakia and tooth
loss/decay increased with fluorosis severity, and increased cancer risks associated with moderate/severe fluorosis were
particularly strong in individuals with more tooth loss/decay. Using a mswaki stick (AOR = 1.7 (1.0, 2.9)) rather than a commercial
tooth brush and infrequent tooth brushing also independently increased risk. Geographic variations showed that areas of high
esophageal cancer incidence and those of high groundwater fluoride levels have remarkably similar locations across Eastern
Africa. In conclusion, poor oral health in combination with, or as a result of, high-altitude susceptibility to hydro-geologically
influenced dental fluorosis may underlie the striking co-location of Africa’s esophageal cancer corridor with the Rift Valley. The
findings call for heightened research into primary prevention opportunities of this highly fatal but common cancer.
