  We show that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to
Brans-Dicke theory in 4D with a self interacting potential and an effective
matter field. The cosmological implication, in the context of FRW models, is
that the observed accelerated expansion of the universe comes naturally from
the condition that the scalar field is not a ghost, i.e., $\omega > - 3/2$. We
find an effective matter-dominated 4D universe which shows accelerated
expansion if $- 3/2 < \omega < - 1$. We study the question of whether
accelerated expansion can be made compatible with large values of $\omega$,
within the framework of a 5D scalar-vacuum Brans-Dicke theory with variable,
instead of constant, parameter $\omega$. In this framework, and based on a
general class of solutions of the field equations, we demonstrate that
accelerated expansion is incompatible with large values of $\omega$.
