Well the dose was initially thought to only provide the material benefit if you are exposed as a child. But it has been found adults also benefit to a lesser extent excluding exposure when they were children. The benefit comes from depositing on the teeth thus effective dosage does not vary greatly with size only the timing of teeth development. Reductions in plague, cavities, bacteria etc reduces rates of cardiovascular disease as well as other ailments which are less closely related.
The harmful effects of fluoride have been studied for decades. Until the same class of scientist that attacked cigarettes before it was public health consensus attack fluoride the comparison isn't relevant.
