Keifr - apparently. Again, the Daily telegraph medical pages on Monday, 24th
A read found out that 4 weeks after substituting kefir yoghurt for the milk on her morning muesli, her sleep improved. It apparently 'contains a high concentration of tryptophan, a precursor of the sleep hormone melatonin. Tryptophan-enriched cereals can help!
Unfortunately they don't state which kefir
