Ask A Scientist: How Come Icelanders Are Lactase Persistent?

Are you lactose intolerant? You may take solace in knowing that you share your condition with most of the world’s population. Icelanders, however, are amongst those lucky chosen few who can digest milk without any discomfort. Why? We asked Dr. Björn Viðar Aðalbjörnsson of the Food Science and Nutrition Department at the University of Iceland to explain:

“As infants, we can digest lactose, when milk is the primary nutrition. Normally for mammals, this is only advantageous in early age and this ability is no longer needed in adult life. Lactase persistence is the ability to digest milk sugar (lactose) as an adult.

“This is a genetic trait that recently evolved in human evolution. There are four genetic variations that cause lactase persistence but around two thirds of the human population do not carry these changes and are lactase non-persistent (and show symptoms of lactose intolerance).

“These changes are more frequent in dairying areas because of a gene/culture coevolutionary process. In Europe, there is one gene that is most common. Some research suggests that this can be traced 7,500 years back, in central Europe, when cattle usage became more prevalent.

“Genetic traits can become more frequent in areas due to natural selection. For example, a long time ago in the Nordic countries (when people could not go to the supermarket to grab a bite), the ability to digest milk as an adult would have been an advantage, especially in times of starvation and famine. Also, milk would have served as a ‘renewable’ nutrition source compared to meat, which requires slaughtering the animal. These factors helped make this ability more common in the Nordic gene pool. This is not, however, exclusive to the Nordic countries, and can be found in other populations where milk was consumed.”