During the three year long assessment phase of the LOFT mission, candidate to the M3 launch opportunity of the ESA Cosmic Vision programme, we estimated and measured the radiation damage of the silicon drift detectors (SDDs) for the satellite instrumentation. In particular, we irradiated the detectors with protons (of 0.8, 11 and 50 MeV energy) to study the increment of leakage current and the variation of the charge collection efficiency produced by the displacement damage, and we "bombarded" the detectors with hypervelocity dust grains to measure the effect of the debris impacts. In this paper we describe the measurements and discuss the results in the context of the LOFT mission.