Lactose intolerance is a result of lactase deficiency where the body is not producing enough of the enzyme lactase, which is usually produced in the small intestine to digest lactose.
If there is not enough lactase, the unabsorbed lactose moves to the colon where bacteria in the colon breaks it down into fatty acids and gases such as carbon dioxide, hydrogen and methane. These fatty acids and gases cause the symptoms of lactose intolerance such as flatulence and bloating.
There are 2 types of lactase deficiency:
- primary lactase deficiency
- secondary lactase deficiency
Primary lactase deficiency is the most common cause of lactose intolerance worldwide. It is due to an inherited genetic fault. Primary lactase deficiency develops when the lactase production decreases as your diet becomes less reliant on milk and dairy products.
This usually occurs after the age of 2 when breastfeeding or bottlefeeding stops, though symptoms may only be noticeable in adulthood.
Secondary lactase deficiency is due to a shortage of lactase caused by a problem in the small intestine. It can occur at any age and may be due to another condition, small intestine surgery or taking certain medications.
Possible reasons include:
- Gastroenteritis
- Celiac disease
- Inflammatory bowel disease
- Chemotherapy
- Long courses of antibiotics.
This decrease in lactase production is usually temporary (which resolves when the causative problem is resolved) but it may also become permanent if it is caused by a long-term problem.
It is also possible to develop secondary lactase deficiency later in life even without another condition to trigger it as our body's production of lactase naturally reduces as we get older.
