Lactose intolerance is a condition that described the inability of the individual to fully digest the lactose sugar from milk. It is described medically as the inability to experience a substantial blood sugar rise following lactose consumption. This digestion normally takes place in the small intestine through secretion of the enzyme lactase. Undigested lactose is problematic because it passes to the colon, where it is fermented by the microflora of the gut. This fermentation results in the production of gasses, which can cause bloating, cramps and discomfort. Lactose digestion is adequate in childhood, but as the individual ages, most lose the inability to digest lactose and therefore develop some degree of lactose intolerance. The ability to digest lactose in adulthood is not the norm, and only the Western mainly white populations of Western Europe, North America and Australasia maintain this ability. The vast majority of the rest of the World are lactose intolerant in adulthood, and this has been suggested to be due to genetic factors.
However, the development of lactose intolerance is complex. There are for example lactose intolerant individuals that can consume yoghurt but not milk. There are also lactose intolerant individuals that can consume milk in small quantities. Some lactose intolerant individuals do not experience discomforting symptoms following consumption of milk, and yet some lactose tolerant individuals do. Based on these findings it is clear that lactose intolerance is actually a sliding grey scale of severity and that prediction of symptoms is not straightforward. There is also evidence that retention of lactose tolerance from childhood is under epigenetic control, rather than being controlled by genetic factors in isolation. In this regard, consumption of large quantities of milk through childhood may increase the chances of lactose tolerance being maintained into adulthood. In other words, exposure to lactose may increase the probability that production and secretion of lactase with be maintained during adulthood.
For example, researchers performed lactose intolerance tests on groups of individuals belonging to the same families1. These families were of African, South American or Asian origin, and so were considered in the at risk of lactose intolerance group. The results of the tests showed that 72 % of the adults were lactose intolerant as measured by blood glucose responses of less than 25 mg per 100 mL following consumption of 50 grams of lactose in 250 mL of water. Only 25 % of the children aged 5 to 7 were lactose intolerant following consumption of 30 grams of lactose in 100 mL water. All of the children under 5 years of age were lactose tolerant, as might be expected, because children have the requirement to digest the lactose in their mother’s milk. The children consumed on average 1.5 grams of milk per day, and the researcher suggested that this might be a contributory factor in the lower rates of lactose intolerance in the 5 to 7 year old children compared to the adults, who drank considerably less milk.
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