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Geographical distribution The distribution of lactose intolerance around the globe shows that not everybody is born identical as far as this disaccharide is concerned. Indeed only 4% of the Scandinavian population is affected by this disease while the incidence increases as one moves more to the south. The countries around the Mediterranean Sea have incidences of the order of 50-75% while in Africa it reaches an amazing 80%. Asia and South-East Asia are affected even more with about 90% of the population suffering from lactose intolerance. On a world scale, three quarters of the total world population is touched by this phenomenon. It must be said that these figures vary a little from study to study. A research group has identified a mutation, not of the gene of the enzyme (lactase) but in a nearby region, in more than 1000 people from five different ethnic backgrounds (Finnish, Chinese, Italian, German and South Korean) which were not affected by lactose intolerance. This is a surprising discovery in the sense that one would rather have expected this type of variant to be detected in the gene that encodes the enzyme and furthermore in individuals that are intolerant to lactose. In fact it probably represents a very old adaptation of the human genome to the environment since it is found in numerous populations of very different origins. According to the authors of this study, this mutation probably appeared at the time when cows became domesticated, leading to the consumption of milk products. They speculate that originally the adult human was not made to digest milk and that thanks to a little help by nature, a gene of lactose tolerance was able to be transmitted from generation to generation. Why are therefore certain individuals still affected by an intolerance of lactose? According to the view of the authors of the study, those people who are intolerant to lactose are in fact carriers of the original gene, i.e. lacking the proximal mutation. |
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