Relationship Between Teeth and Functional Capacity: Effect or Association?

Objectives: Tooth loss is associated with poor functional capacity. However, there is no conclusive relevant causal evidence. We investigated the causal effect of tooth loss on the instrumental activity of daily living (IADL) among older adults aged ≥50 years old in England, using exogenous geographical and historical variation in the coverage of fluoridated water.
Methods: Data from the English Longitudinal Study of Aging (ELSA) wave 7 (2014–2015) was analyzed. Participants were asked to report any limitations in IADL (preparing a hot meal, shopping for groceries, making telephone calls, taking medications, doing work around the house or garden, or managing money) and their number of teeth (0, 1–9, 10–19, and ≥20 teeth). The annual coverage of naturally/artificially fluoridated water in their region of residence when they were between 5 to 20 years of age was totalized and used as the instrumental variable (IV) for the number of teeth to consider potential confounders including unmeasured ones. Linear probability model adjusted for age, sex, and the regional fixed effect was fitted by Two-Stage Least Squares estimation.
Results: We analyzed data on 9,437 respondents (average age = 67.7 years old, 44.7% were men). The first-stage regression showed that being exposed to fluoridated water was associated with having more teeth (coefficient = 1.05; 95% confidence interval, CI: 0.68, 1.43; F = 30.09). The second-stage regression showed the causal effect of tooth loss on IADL that retaining one more tooth reduced the probability of having a limitation in IADL by 1.9 percentage points (coefficient = -0.019; 95% CI: -0.035, -0.004).
Conclusions: There is a causal effect of tooth loss on the ability to carry out main daily activities among older adults in England. The finding also suggested that being exposed to fluoridated water before adulthood prevent tooth loss at an older age. Promoting dental health should be one of the key targets for maintaining functional capacity and healthy aging.