In the framework of quantum gravity propagating in large extra dimensions, the effects of virtual Kaluza-Klein graviton and graviscalar interference with Higgs boson production amplitudes are computed at linear colliders and Higgs factories. The interference of the almost-continuous spectrum of the KK gravitons with the standard model resonant amplitude is finite and predictable in terms of the fundamental D-dimensional Plank scale MD and the number of extra dimensions delta. We find that, for MD simeq 1 TeV and delta = 2, effects of the order of a few percent could be detected for heavy Higgs bosons (mH>500 GeV) in Higgs production both via WW fusion in e+e- colliders and at mu+mu- Higgs-boson factories.
