What Causes Lactose Intolerance?
Lactase production by the bowel cells starts in fetal life by the 8th week and reaches its peak by birth, Nature’s plan to prepare baby for its first diet. But almost all mammals lose the ability to produce lactase after few months of birth, by and large humans are no exception. The incidence of lactose intolerance varies with age, geographically with ethnicity and race, and may be congenital or acquired. [2]
Based on the underlying causes the heading is discussed in three subtypes:
Primary lactose intolerance:
This accounts for the commonly seen progressive decrease in production of lactase from infancy to adulthood as seen in most Asian and African communities. The onset of symptoms is rare before the age of six. The gradient with age varies in different ethnic communities and also in different mammal species. 2% of northern European community is seen to have lactase insufficiency. The graph significantly rises to an estimated 50-80% in people with Hispanic ethnicity. Topping the chart, nearly 80-100% of adult African and Asian develop primary lactose intolerance. The study of ancient DNA suggest that our ancestors too had the same pattern of lactase hypo production after weaning. This means that it’s natural and intrinsic through generations. However, the northern European community is seen to sway from this pattern by continuing to produce lactase even into adulthood. There is a surprising paradox at work here which revolves around the concepts of evolution and natural selection. The variation geographically is attributed to the start of dairy farming 10,000 years ago in that region. Those whose diet consisted primarily of milk developed an evolutionary trait to persistently produce lactase throughout their life. On the other hand, people having generational history of a diet that lacks significant milk proportions did not require the evolutionary change to produce lactase significantly and hence can do with primary levels of lactase production. They develop lactose intolerance if they consume ample lactose as their bodies are not prepared to cope with excess of it. There is a certain genetic polymorphism seen in their DNA makeup which is responsible for it. We don’t know more at molecular levels but it seems both environmental and genetic factors are at play here. It may be hypothesized by stated facts then that maybe adult mammals’ diet is not planned to include milk. By this research lactase persistence is seen as mutation and not hypolactasia, as believed in the theory discussed next.
The second theory goes otherwise to state that mammals fundamentally produce lactase and it’s the commercializing of milk and dairy products over decades that have resulted in engineered forms that lack, or contain components other than natural. Our bodies adapted to these unnatural forms by mutating its lactase gene to stop expression once we reach adulthood. This theory is poorly supported on the grounds of research of ancient DNA and comparative analysis on other mammals. It’s quite a paradoxical way to look at this old problem.