I've just watched a fascinating Royal Institute lecture by a Canadian scientist on the role that the microbes that co-exist with us have on our health. From obesity to Alzhemers and Parkinsons, asthma and lactose tolerance, the effects of keeping a dog or overdoing it regarding hygiene, it's all covered, and some of it is seriously surprising. I'd particularly urge anyone thinking of having children or with very young children to watch this right through.
https://www.youtube.com/watch?v=xlEFI5A3QFM
All I can say is thank goodness I tend to like Italian food - but I am going to increase how many times I brush my teeth up to three times a day now, having seen this!