  Kaluza-Klein fields characterizing, from a four-dimensional viewpoint, the
presence of compact universal extra dimensions would alter low-energy
observables through effects determined by some compactification scale,
$R^{-1}$, since the one-loop level, thus being particularly relevant for
physical phenomena forbidden at tree level by the Standard Model. The present
paper explores, for the case of one universal extra dimension, such new-physics
contributions to Higgs decays $h^{(0)}\to q^{(0)}_\alpha q^{(0)}_\beta$, into
pairs of quarks with different flavors, a sort of decay process which, in the
Standard Model, strictly occurs at the loop level. Finite results, decoupling
as $R^{-1}\to \infty$, are calculated. Approximate short expressions, valid for
large compactification scales, are provided. We estimate that Kaluza-Klein
contributions lie below predictions from the Standard Model, being about 2 to 3
orders of magnitude smaller for compactification scales within $1.4\,{\rm
TeV}<R^{-1}<10\,{\rm TeV}$.
