Editors

IrmaJärvelä

Kaija-LeenaKolho

Lactose Intolerance

Lactose intolerance should be identified as the cause of flatulence, abdominal pains and intermittent diarrhoea before performing more extensive investigations.
Genetic testing for adult-type hypolactasia (primary hypolactasia, genotype C/C₁₃₉₁₀) reliably confirms or excludes the predisposition to ordinary lactose intolerance.
Lactose intolerance is rare in children below 5 years of age http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5726035/. Find out about local epidemiology.
A lactose ingestion test frequently yields false results and has become obsolete.
Lactose as an ingredient of pharmaceutical tablets very rarely causes symptoms.
Coeliac disease Coeliac Disease is the most important aetiology of secondary hypolactasia and should be excluded as the cause of lactose intolerance.

Adult-type hypolactasia is defined as decreased lactase activity inherited as an autosomal recessive trait.
Lactose intolerance is defined as symptomatic hypolactasia.
Secondary hypolactasia may be a result of coeliac disease Coeliac Disease or chronic infection of the bowel (e.g. giardiasis Giardiasis).
Incidental hypolactasia is not always the only cause of the patient's abdominal symptoms, and hypolactasia does not cause anaemia or malabsorption of nutrients.
The symptoms are the result of lactose absorbing water in the intestine by osmosis, which speeds intestinal transport. Lactose is then metabolized by colonic bacteria producing gas.

The prevalence of adult-type hypolactasia varies in different populations. In Northern European inhabitants it occurs in 18%.
In children hypolactasia rarely develops before the age of 5 years. School-aged children often have milk-induced complaints associated with hypolactasia.

Flatulence and meteorism
Ill-defined abdominal pain
Diarrhoea
The symptoms start 1-2 hours after a lactose-containing meal, sometimes even later because the rate of stomach emptying affects the symptoms.
Symptoms depend on the amount of ingested lactose.
Some people with the genotype for hypolactasia spontaneously reduce drinking of milk already in childhood.
It is very uncommon for lactose as an ingredient of tablets to cause symptoms.

If the patient's symptoms are clearly alleviated by reducing lactose intake, or removing it completely from the diet, diagnostic testing is not a must.
- The amount of lactose tolerated vary between individuals. Most tolerate it to some extent especially in association with meals.
The diagnosis was earlier based on the lactose tolerance test showing marginal increase in blood glucose concentration together with typical symptoms. The test is, however, laborious and its accuracy is low in comparison with the gene test. Consequently, it is no longer in use.

A gene test, which can be performed from a blood sample, gives indirectly information on the lactase activity in an adult person. The test can be used to confirm clinical suspicion.
- C/C genotype₁₃₉₁₀ = genotype associated with hypolactasia, i.e. low lactase activity
- Lactase activity gradually decreases at the age of 5 to 12 years. Therefore, the gene test in children less than 12 years of age is indicative only. There may be differences between populations. Find out about local situation.
- Genotypes C/T₁₃₉₁₀ and T/T₁₃₉₁₀ as a rule exclude primary hypolactasia in all age groups. In addition to these, however, there are other, rare gene variants that may contribute to the development of lactose intolerance.

Decrease the amount of lactose in the food (in the majority of patients one glass of milk, consumed with meal, does not result in symptoms) http://www.dynamed.com/condition/lactose-intolerance-in-adults#DIET; cf. coeliac disease where an absolutely gluten-free diet is mandatory.
Sour milk products can be tried because they contain relatively small amounts of lactose. Ripened cheese does not contain lactose.
Low-lactose products contain less than 1% lactose (ordinary dairy products contain about 4.8%). Some persons with hypolactasia feel better if they abstain from low-lactose products as well, i.e. exclude such milk or cream from their diet.
Patients with severe symptoms should remember that also the following products, when made with milk, contain lactose: bread and other bakery products, butter, mashed potatoes and milk chocolate.
Adequate calcium intake should be ensured by using cheese or calcium preparations, if milk products otherwise are completely excluded from the diet.
Ask the patient to consult again if the symptoms do not disappear with a lactose-free diet. Usually the cause is non-compliance with the diet, but the patient may also have coeliac disease or some other form of malabsorption causing lactose malabsorption.
Products containing lactase enzyme http://www.dynamed.com/condition/lactose-intolerance-in-adults#MEDICATIONS are suitable for adults for temporary management of symptoms, but they are not recommended for children to compensate for the lack of lactase.

Cano-Contreras AD, Minero Alfaro IJ, Medina López VM ym. Efficacy of i3.1 Probiotic on Improvement of Lactose Intolerance Symptoms: A Randomized, Placebo-controlled Clinical Trial. J Clin Gastroenterol 2020;():. [PubMed]
Shaukat A, Levitt MD, Taylor BC ym. Systematic review: effective management strategies for lactose intolerance. Ann Intern Med 2010;152(12):797-803. [PubMed]
Wilt TJ, Shaukat A, Shamliyan T ym. Lactose intolerance and health. Evid Rep Technol Assess (Full Rep) 2010;(192):1-410. [PubMed]