Often, affected individuals have difficulty digesting fresh milk but can eat certain dairy products such as cheese or yogurt without discomfort. These foods are made using fermentation processes that break down much of the lactose in milk.
Lactose intolerance in infancy resulting from congenital lactase deficiency is a rare disorder. Its incidence is unknown. This condition is most common in Finland, where it affects an estimated 1 in 60, newborns.
Approximately 65 percent of the human population has a reduced ability to digest lactose after infancy. Lactose intolerance in adulthood is most prevalent in people of East Asian descent, with 70 to percent of people affected in these communities. The prevalence of lactose intolerance is lowest in populations with a long history of dependence on unfermented milk products as an important food source.
For example, only about 5 percent of people of Northern European descent are lactose intolerant. Lactose intolerance in infants congenital lactase deficiency is caused by mutations in the LCT gene. The LCT gene provides instructions for making the lactase enzyme. Mutations that cause congenital lactase deficiency are believed to interfere with the function of lactase, causing affected infants to have a severely impaired ability to digest lactose in breast milk or formula.
Lactose intolerance in adulthood is caused by gradually decreasing activity expression of the LCT gene after infancy, which occurs in most humans. Some individuals have inherited changes in this element that lead to sustained lactase production in the small intestine and the ability to digest lactose throughout life. People without these changes have a reduced ability to digest lactose as they get older, resulting in the signs and symptoms of lactose intolerance. The type of lactose intolerance that occurs in infants congenital lactase deficiency is inherited in an autosomal recessive pattern , which means both copies of the LCT gene in each cell have mutations.
The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. The ability to digest lactose into adulthood depends on which variations in the regulatory element within the MCM6 gene individuals have inherited from their parents.
The variations that promote continued lactase production are considered autosomal dominant , which means one copy of the altered regulatory element in each cell is sufficient to sustain lactase production. People who have not inherited these variations from either parent will have some degree of lactose intolerance. Many Australian babies are unnecessarily weaned because their irritability is wrongly assumed to be lactose intolerance. In reality, the severe form of this condition — known as primary or congenital lactose intolerance where the infant does not produce lactase from birth — is very rare.
Secondary lactose intolerance is more common. This can occur temporarily after a bout of gastroenteritis , for example, but often improves after several weeks as the lining of the gut heals. It is important not to eliminate dairy foods completely from your diet if lactose intolerance is suspected, as dairy foods are rich sources of nutrients.
Some dairy products such as hard and mature cheeses contain no lactose, and others such as cream, butter, cottage cheese and ricotta contain very little. Many people with lactose intolerance can tolerate small amounts of lactose with minimal symptoms.
The enzyme lactase breaks down milk sugar lactose. Lactase enzymes are found in the lining of the small intestine. They change the milk sugar into absorbable compounds — glucose and galactose. If your body does not produce enough lactase, lactose is not digested and absorbed in the small intestine in the usual way. Instead, it continues to travel along the digestive tract to the large intestine, where bacteria partially break it down into acids and gases.
This fermentation process causes excessive wind, bloating and associated pain. Any undigested lactose continues along the intestinal tract. This lactose attracts water molecules.
So rather than being absorbed into the bloodstream, water remains in the faecal matter poo and watery poo diarrhoea is the result. Lactose intolerance is largely genetically determined — where your genetic make-up causes you to have less lactase than usual. Some other causes include:. There are two types of lactose intolerance in babies: primary and secondary lactose intolerance. Primary lactose intolerance or congenital lactose intolerance is a very rare genetic condition.
Babies with this condition are born without any lactase enzymes at all. They cannot process or absorb lactose. They fail to thrive from birth, and have severe diarrhoea from the day they are born. They are diagnosed straight after birth. Babies with this condition must be fed feeds free of lactose. Secondary lactose intolerance occurs when the gut lining where lactase is produced is damaged. This can occur due to a bout of gastroenteritis or due to chronic irritation such as that due to food allergy or food intolerance , among other reasons.
Breastfed babies experiencing symptoms of lactose intolerance but who do not have primary lactose intolerance should continue to breastfeed. Once the source of the damage is removed, their gut will heal and produce lactase again. There is no need for women who are breastfeeding to reduce or cut out dairy foods if their baby is showing signs of lactose intolerance.
Regardless of what they eat or drink, the level of lactose in breastmilk stays at around seven per cent. For formula-fed babies, there is no benefit in using lactose-free formula unless the baby is losing weight.
Lactase drops are available from pharmacies, but are not always helpful. If your baby is showing signs of lactose intolerance, such as excessive bowel motions, wind in the bowel, and pain, have your baby checked by your GP for any medical problems such as infection.
Check that your baby is gaining weight and growing normally. Common signs and symptoms include:. Make an appointment with your doctor if you frequently have symptoms of lactose intolerance after eating dairy foods, particularly if you're worried about getting enough calcium. There is a problem with information submitted for this request.
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You will also receive emails from Mayo Clinic on the latest health news, research, and care. Lactose intolerance occurs when your small intestine doesn't produce enough of an enzyme lactase to digest milk sugar lactose.
Normally, lactase turns milk sugar into two simple sugars — glucose and galactose — which are absorbed into the bloodstream through the intestinal lining. If you're lactase deficient, lactose in your food moves into the colon instead of being processed and absorbed.
In the colon, normal bacteria interact with undigested lactose, causing the signs and symptoms of lactose intolerance. There are three types of lactose intolerance. Different factors cause the lactase deficiency underlying each type.
People who develop primary lactose intolerance — the most common type — start life producing enough lactase.
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