How common is lactose intolerance?

In Ireland, only about 4-5 % of the population are affected by lactose intolerance. Worldwide, the prevalence is estimated at about 65 % but it varies largely across populations, ranging from 4 % to over 80 % across different parts of the world. The lower prevalence in Ireland is due to a genetic trait that makes us efficient at digesting lactose, the naturally occurring milk sugar.

This genetic trait, known as lactase persistence, is recognised as an ‘evolutionary advantage’, that arose in populations that farmed dairy animals. The consumption of milk provided an advantage in nutritional acquisition as dairy foods provide a wide range of vitamins and minerals.