Lactose intolerance

Lactose is a sugar found naturally in milk. It’s important to distinguish between lactose intolerance and milk allergy, because milk allergy can cause severe reactions.
Lactose intolerance is caused by a shortage of the enzyme lactase, which is needed to break down lactose so it can be absorbed into the bloodstream. When someone doesn’t have enough of this enzyme, lactose isn’t absorbed properly from the gut, which can cause symptoms such as bloating and diarrhoea.

Lactose intolerance can be caused by a number of things. In humans, the body produces less lactase after the age of two. However, in white Western Europeans, lactase can be produced into adult life, which allows lactose to be broken down properly.

Because of this, lactose intolerance is more common in certain ethnic and racial populations than in others. In the UK, we think about 5% of the general population have lactose intolerance. In communities where milk is not traditionally part of the typical adult diet, a much bigger proportion of people are affected. For example, up to 75% of the black African community and more than 90% of the Asian community are intolerant to lactose.

Digestive diseases, or injuries to the small intestine can sometimes cause lactose intolerance, because they reduce the amount of lactase produced. In rare cases, the condition can be inherited.

Milk from mammals including cows, goats, sheep and humans contain lactose. This means that goats’ milk and sheep milk aren’t suitable alternatives to cows’ milk for people who are intolerant to lactose. There is no medical treatment for lactose intolerance, but symptoms can be avoided by controlling the amount of lactose in the diet. Adults with lactose intolerance can often have a small amount of milk without getting any symptoms.
(See last table for info on egg products). Intolerance should not be confused with allergy. See Symptoms of below.

Milk Allergy
Allergy to cows’ milk is the most common food allergy in childhood, and affects 2-7% of babies under one year old. It’s more common in babies with atopic dermatitis. A reaction can be triggered by small amounts of milk, either passed to the baby through the mother’s breast milk from dairy products she has eaten, or from feeding cows’ milk to the baby.
Children usually grow out of milk allergy by the age of three, but about a fifth of children who have an allergy to cows’ milk will still be allergic to it as adults. The symptoms of milk allergy are often mild and can affect any part of the body. They can include rashes, diarrhoea, vomiting, stomach cramps and difficulty in breathing. In a very few cases, milk allergy can cause anaphylaxis.

Cows’ milk allergy is caused by a reaction to a number of allergens in cows’ milk, such as casein and whey. Casein is the curd that forms when milk sours, and whey is the watery part that is left when the curd is removed.

People can be allergic to either whey or casein, or both, and an allergic reaction can be triggered by very small amounts of these allergens in people who are sensitive. Heat treatment, such as pasteurisation, changes whey, so people who are sensitive to whey might not react to pasteurised milk. But heat treatment doesn’t affect casein, so someone who is allergic to casein will probably react to all types of milk and milk products.

Milk from other mammals (such as goats and sheep), and hydrolysed milk and soya formulas, are sometimes used as a substitute for babies who are at risk of developing cows’ milk allergy. However, the allergens in milk from goats and sheep are very similar to those in cows’ milk. This means that someone with a cows’ milk allergy might react to these other types of milk as well, so goat’s and sheep milk aren’t suitable alternatives for people who are sensitive to cows’ milk.

Some highly hydrolysed milk formulas are suitable for babies with cows’ milk allergy, but other types of formula, such as partially hydrolysed milk and soya formulas, aren’t suitable, because many babies with cows’ milk allergy might react to them as well.