About Lactose intolerance

Lactose intolerance is a common digestive problem, which gives rise to symptoms such as gas, diarrhea, bloating or pains. Lactose is found primarily in dairy products, but also as an additive in other products, e.g. certain chips and powdered products.

Lactose intolerance is a common digestive problem. A person that is lactose intolerant lacks the enzyme lactase in the small intestine, which is needed to digest milk sugar molecules. This means that lactose can not be absorbed by the intestine and is instead broken down in a process involving intestinal bacterias. This process gives rise to symptoms such as gas, diarrhea, bloating or pains. Lactose is found primarily in dairy products, but also as an additive in other products, e.g. certain chips and powdered products.

There are three different forms of lactase deficiency:

Primary lactose intolerance, which is the most common form. The age at which the associated digestive problems arise varies between individuals: However most commonly lactase deficiency occurs during adulthood. The capacity to form lactase cannot be regained, but a certain capacity may remain, which means that small quantities of lactose can still be broken down.

Secondary lactase deficiency appears in connection with some other injury to the intestine. With untreated gluten hypersensitivity, inflammation in the intestine, severe stomach flu or after an abdominal operation, the intestinal membrane may be damaged in such a way that it can not produce lactase. When the injury is healed, most often the capacity to produce lactase returns.

Congenital lactase deficiency is extremely uncommon and is often discovered when the child is nursing or receives a substitute for mother's milk.

In case of primary lactose intolerance, the deficiency of enzyme lactase depends on inherited genetic variation. Evolutionary speaking, it was discovered that ability to digest lactose was beneficial for populations where milk products were included in diet, therefore mutations have arisen that led to tolerance of lactose. However, there is still a small proportion of individuals in those populations that have the genetic variant associated with lactose intolerance. Two parents who are lactose tolerant can have children who are lactose intolerant.

The map below shows percentage proportion of individuals in the world that do not have any deficiency of lactase enzyme and therefore are able to digest lactose.

Figure: Interpolated map showing frequency of individuals with ability to digest lactose  (lactose persistent, LP). The dots on the map represent locations where the data was collected. The coloured scale on the side shows the calculated frequency of LP- individuals. (Itan et al. BMC Evol Biol. 2010 Feb 9;10:36).

There are several mutations (single nucleotide polumorphism, SNP) described, that contribute to down-regulation of lactase gene. Different studies, e.g in Finland, have indentified a SNP at position 13910 (C>T) upstream of lactase gene, that shows to have a full association with lactose intolerance. It is this position 13910 (C>T)  that is analyzed in Dynamic Code’s lactose intolerance test. This SNP is common for European population, but for the other populations e.g. some groups in Africa and Middle East, with a considerable proportion of lactose intolerant individuals, the correlation between the genotype in position 13910 and lactose intolerance /tolerance could not be shown. However there are other mutations reported that are associated with lactose intolerance for these populations.

How can I tell if I am lactose intolerant?

If lactose cannot be broken down in the small intestine, the lactose will be fermented by bacteria in the large intestine and give rise to gas. The gas formation and the water-absorbent effect of the lactose produce symptoms such as diarrhea, bloating, stomach gurgling and colic pains. The symptoms may vary from person to person. Some people tolerate dairy products in small quantities and others not at all.

What should I do if I am lactose intolerant?

If you are lactose intolerant you should avoid or limit the intake of products that contain lactose. This is a simple way for you to get rid of your discomforts. The enzyme lactase may also be added to the diet. If you want more help or advice you can contact a physician or a dietician. 


Reviewed: 2019-02-22

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