  We show that Brans-Dicke (BD) theory in 5D may explain the present cosmic
accelerated expansion without recurring to matter fields in 5D or dark energy
in 4D. Without making any assumption on the nature of the extra coordinate or
the matter content in 5D, here we demonstrate that the vacuum BD field
equations in 5D are equivalent, on every hypersurface orthogonal to the extra
dimension, to a BD theory in 4D with a self interacting potential and an
effective matter field. The potential is not introduced by hand, instead the
reduction procedure provides an expression that determines its shape up to a
constant of integration. It also establishes the explicit formulae for the
effective matter in 4D. In the context of FRW cosmologies, we show that the
reduced BD theory gives rise to models for accelerated expansion of a
matter-dominated universe which are consistent with current observations and
with a decelerating radiation-dominated epoch.
