John Snow’s theory of rickets
John Snow was born in 1813, the son of a labourer in Yorkshire. He was responsible for one of the most celebrated acts in medical history when, on 2 September 1854 he cut short an outbreak of cholera in London by getting the handle of the Bond Street pump disconnected. He was also a pioneer in the development of anaesthesia. It is less well known that in 1857, less than a year before he died, he wrote an article on rickets which was published in the Lancet. That article is reprinted along with three commentaries in the
Snow lists poor air quality, poor diet, lack of exercise and “a scrofulous taint” as factors thought in the mid-19th century to contribute to rickets. He had trained and practised in Newcastle-upon-Tyne and Yorkshire before moving to London and observed that children in the northern cities and towns were less prone to rickets though they were equally exposed to the dismal living conditions of the industrial revolution. People in the north of England usually baked their own bread whereas in London they would buy it from bakers who added large amounts of alum (potassium aluminium phosphate) to make the bread whiter and add weight to it. Snow argued that the alum would convert calcium carbonate in flour to insoluble calcium salts and therefore deprive the bone of “phosphate of lime”. He cited the work of the German chemist, Liebig, to support his views and himself analysed London bread, finding 10.13 grains of alum in 500 grains of bread. He suggested epidemiological study of the relationship between baker’s bread and rickets but claimed to be too busy to collect data himself. He called for the committees of the public hospitals and the guardians of the poor to insist on being supplied with unadulterated bread. (The adulteration of flour was illegal but bakers were never prosecuted.)
Was Snow right? Two of the commentators refer to evidence that phosphate binding by aluminium salts may produce rickets in children or osteomalacia in adults. One suggests that mid-19th century London bones might be analysed for aluminium. Whether he was right or wrong, Snow’s 1857 paper shows an active scientific mind at work.