Lactase persistence

Lactase persistence is the continued activity of the lactase enzyme in adulthood, allowing the digestion of lactose in milk. In most mammals, the activity of the enzyme is dramatically reduced after weaning. In some human populations, though, lactase persistence has recently evolved as an adaptation to the consumption of nonhuman milk and dairy products beyond infancy. Lactase persistence is very high among northern Europeans, especially Irish people. Worldwide, most people are lactase non-persistent, and are affected by varying degrees of lactose intolerance as adults. However, lactase persistence and lactose intolerance do not always overlap. The distribution of the lactase persistence (LP) phenotype, or the ability to digest lactose into adulthood, is not homogeneous in the world. Lactase persistence frequencies are highly variable. In Europe, the distribution of the lactase persistence phenotype is clinal, with frequencies ranging from 15–54% in the south-east to 89–96% in the north-west. For example, only 17% of Greeks and 14% of Sardinians are predicted to possess this phenotype, while around 80% of Finns and Hungarians and 100% of Irish people are predicted to be lactase persistent. Similarly, the frequency of lactase-persistence is clinal in India, a 2011 study of 2,284 individuals identifying a prevalence of LP in the Ror community, of Haryana, in the North West, of 48.95%, declining to 1.5% in the Andamanese, of the South East, and 0.8% in the Tibeto-Burman communities, of the North East. High frequencies of lactase persistence are also found in some places in Sub-Saharan Africa and in the Middle East. But the most common situation is intermediate to low lactase persistence: intermediate (11 to 32%) in Central Asia, low (