Lactose intolerance should be recognized (or ruled out) as the cause of flatulence, abdominal pain and intermittent diarrhoea before performing more extensive investigations.
Primary, or adult-type, hypolactasia signifies a genetically defined decrease in intestinal lactase levels with age. It is not a disease but a genetic trait.
Primary hypolactasia as the cause of lactose intolerance can be excluded by genetic testing. This does not exclude lactose intolerance due to other causes.
Any disease damaging small intestinal villi can cause lactase deficiency; in this case, the condition is called secondary hypolactasia.
Coeliac disease Coeliac Disease is the most important aetiology of secondary hypolactasia and should be excluded as the cause of lactose intolerance.
In lactose intolerance, the symptoms occur when lactose remaining in the intestine absorbs water by osmosis and speeds intestinal transport. The lactose is then metabolized by colonic bacteria producing gas.
Secondary hypolactasia may be a result of coeliac disease Coeliac Disease or persistent bowel infection (e.g. giardiasis Giardiasis) or damaged intestinal villi following severe diarrhoea, for instance.
Epidemiology
The prevalence of primary hypolactasia varies in different populations. Globally, approximately 2 in 3 persons have lactose malabsorption. There is great variation in regional prevalence, ranging from about 28% in northern, southern and western Europe (in some countries below 10%) to most of the population in sub-Saharan Africa, Middle East and Asia (in South Korea 100%) http://www.thelancet.com/journals/langas/article/PIIS2468-1253(17)30154-1/fulltext (the study excluded children below 10 years of age).
Milk-induced complaints in school aged children are often associated with primary hypolactasia.
Symptoms
Abdominal bloating and meteorism
Ill-defined abdominal pain
Diarrhoea
The symptoms start 1-2 hours after a lactose-containing meal, sometimes even later because the symptoms are influenced by the rate of stomach emptying and the amount of ingested lactose.
Many people spontaneously reduce consumption of milk in childhood already.
Some may be subjectively asymptomatic.
It is very uncommon for lactose as an ingredient of tablet medication to cause symptoms.
Diagnostics
If the patient's symptoms are clearly alleviated by reducing lactose intake, or eliminating it completely from the diet, diagnostic testing for hypolactasia is not a must.
In primary hypolactasia, the amount of lactose tolerated varies between individuals. Most people tolerate it to some extent especially in association with meals.
Laboratory examinations
If the diagnosis remains uncertain (leaving out or reducing lactose intake does not influence the symptoms), adult-type primary hypolactasia can be confirmed by doing a gene test on a venous blood sample.
Gene test for primary hypolactasia
Gives indirect information on the lactase activity in an adult person. The test can be used to confirm a clinical suspicion.
C/C13910 genotype = genotype associated with hypolactasia, i.e. low lactase activity
Check local guidance concerning interpretation of the test result. For example in Finnish children with primary hypolactasia, 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.
Genotypes C/T13910 and T/T13910 as a rule exclude primary hypolactasia in all age groups, and these people show high lactase activity throughout life.
In addition to the C/C13910 genotype, there are other, rare gene variants that may affect the expression of the lactase enzyme and contribute to decreased lactase levels. There is currently no gene test available for them.
It should be kept in mind that cutting down on lactose will also alleviate the symptoms in patients with secondary hypolactasia.
Coeliac disease, for example, may cause secondary hypolactasia due to damaged intestinal villi, and excluding coeliac disease is therefore recommended.
Primary hypolactasia will not affect the blood count (causing anaemia, for instance) or cause increased inflammatory markers.
Treatment
Decrease the amount of lactose in the food in people with the hypolactasia genotype (C/C13910; in the majority of patients about one glass of milk, consumed with a meal, does not result in symptoms); cf. coeliac disease, where a 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 people with lactose intolerance feel better if they also abstain from low-lactose milk or cream.
Patients with severe symptoms should remember that the following products, when made with milk, also 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 dairy products are otherwise completely excluded from the diet.
In differential diagnosis, GI diseases and protozoal infections should be kept in mind, particularly if the response to dietary changes is poor.
Products containing lactase enzyme are suitable for controlling transient symptoms in adults, but they are not recommended to compensate for low lactase levels in children.
References
Järvelä I, Torniainen S, Kolho KL. Molecular genetics of human lactase deficiencies. Ann Med 2009;41(8):568-75 [PubMed]
Rasinperä H, Savilahti E, Enattah NS, et al. A genetic test which can be used to diagnose adult-type hypolactasia in children. Gut 2004;53(11):1571-6 [PubMed]
Enattah NS, Sahi T, Savilahti E, et al. Identification of a variant associated with adult-type hypolactasia. Nat Genet 2002;30(2):233-7 [PubMed]