Complex sentence: All reviews to date have suffered from the variability of the studies which have been assessed; future large-scale randomized trials are necessary to determine whether the benefits from zinc treatment for colds outweigh the disadvantages.
Split into simpler sentences: All reviews to date have suffered from the variability of the studies which have been assessed. Future, large-scale, randomized trials are necessary to determine whether the benefits from zinc treatment for colds outweigh the disadvantages.