Medicine Newbie: Lactase deficiency

Friday, 4 April 2014

Lactase deficiency

Synonyms
Lactose intolerance
Lactase deficiency
Hypolactasia

Terminologies
Lactose: a disaccharide made up of galactose and glucose
Lactase: an enzyme that splits lactose

Cause
Patients lack the enzyme lactase (lactase deficiency) and therefore cannot digest lactose, a milk sugar, which is also found in processed dairy foods. They cannot tolerate milk and dairy products (lactose intolerance) and suffer from diarrhoea if they take such foods.

What is lactose?
Lactose is a water-soluble compound. Lactose is a sugar found in milk. Chemically and structurally, lactose is a disaccharide, meaning it is a compound made up of 2 simple sugars - glucose and galactose. Lactose can be split by the enzyme lactase to give the 2 simple sugars (called monosaccharides).

Enzyme action
The enzyme lactase is found in the duodenum (first part of the small intestines). Lactase breaks down lactose to glucose and galactose.

Symptoms
Consumption of foods containing significant amounts of lactose (minus added lactase) causes symptoms which may include:

abdominal bloating and
cramps,
flatulence,
diarrhea,
nausea,
borborygmi (rumbling stomach), or
vomiting.

Precautions

As a genetic disorder, lactose intolerance prevents babies from drinking human breast milk, which nearly quarters its risk of Sudden Infant Death Syndrome.
Some studies have produced evidence that milk consumption by lactose intolerant individuals may be a significant cause of inflammatory bowel disease.

Types of lactase deficiency

There are 3 types of lactase deficiency:

Primary (genetic; only affects adults) - most common
Secondary (acquired or develops due to damage of duodenum) - transient
Congenital (present at birth; rare; autosomal recessive; affects babies) - babies cannot consume breast milk

Lactase levels
Lactase levels vary widely depending on age, population and food consumption.

Lactase levels decrease after weaning from milk, and children become lactose intolerant after weaning.
Lactase levels persist into adulthood if children are not weaned from dairy products.
75% adults have decreased lactase levels.
5% adults in northern Europe have decreased lactase levels (they could reflect resident migrants).
71% adults of Sicily have reduced lactase levels (Sicily is a Mediterranean country).
90% adult Africans and Asians have lactase deficiency (a small 10% can tolerate milk - they could be resident Caucasians).
Lactase persistence could be due to genetic mutation.

Dairy foods that contain lactose:

milk (full-cream and skimmed)
yoghurt (fresh and frozen)
cheese (soft and hard)
butter

Non dairy foods containing lactose

Label reading is essential, as commercial terminology varies according to language and region. Lactose is present in two large food categories—conventional dairy products, and as a food additive (casein, caseinate, whey), which may contain traces of lactose. Food additives are used for adjusting the texture, flavour and adhesive qualities of processed food. Milk and milk products are often added to processed foods—foods that have been altered to prolong their shelf life. People with lactose intolerance should be aware of the many food products that may contain even small amounts of lactose.

lactoserum,
casein,
caseinate,
whey,
milk solids,
modified milk ingredients
meats (sausages/hot dogs, sliced meats, pâtés),
gravy stock powder,
margarines,
sliced breads,
breakfast cereals,
potato chips,
medications,
pre-prepared meals,
meal replacement (powders and bars),
protein supplements (powders and bars)
barbecue sauces and
liquid cheeses used in fast-food restaurants
bread and other baked goods
waffles,
pancakes,
biscuits, cookies, and mixes
processed breakfast foods (doughnuts, frozen waffles and pancakes, toaster pastries, and sweet rolls)
processed breakfast cereals
instant potatoes,
soups, and
breakfast drinks
potato chips,
corn chips, and other processed snacks
processed meats (beef, sausage, hot dogs, and lunch meats),
salad dressings
liquid and powdered milk-based meal replacements
candies
non-dairy liquid and powdered coffee creamers (made from palm oil)
non-dairy whipped toppings

Diagnosis

The patient is challenged with food containing high lactose, and is monitored for 30 minutes to 2 hours for clinical symptoms of lactose intolerance.

Confirmatory tests

After lactose intolerance is diagnosed, confirmatory tests are done. There 6 ways to confirm lactose intolerance. The choice of tests selected are based on the patient's age (infant, adult) and condition (pregnancy) and clinical laboratory facilities available.

Hydrogen breath test - Elevated hydrogen levels indicate lactose intolerance.
Blood glucose test - needs overnight fasting. Take 1st blood sample and administer 50g lactose (solution). Blood is then drawn again at 30 minute, 1-hour, 2-hours, and 3-hours. If the lactose cannot be digested, blood glucose levels will rise by less than 20 mg/dL.
Stool acidity test - This test can be used to diagnose lactose intolerance in infants. The infant is given lactose to drink. If the infant is tolerant, the lactose is digested and absorbed in the small intestine; otherwise it is not digested and not absorbed and it reaches the colon. The bacteria in the colon, mixed with the lactose, cause acidity in stools. Stools passed after the ingestion of the lactose are tested for level of acidity. If the stools are acidic, the infant is intolerant to lactose. Stool pH in lactose intolerance is less than 5.5 (acidic stools).
Intestinal biopsy - This is done after a positive hydrogen breath test. A gastrointestinal endoscopy is done to confirm lactase deficiency. a) Modern techniques have enabled a bedside test to identify the presence of lactase enzyme on upper gastrointestinal endoscopy instruments. b) However, for research applications such as mRNA measurements, a specialist laboratory is required. The amount of mRNA present is determined by rPCR.
Stool sugar chromatography - details?
Genetic diagnosis - It is used in primary lactose intolerance. Lactase activity persistence in adults is associated with two polymorphisms: C/T 13910 and G/A 22018 located in MCM6 gene. These polymorphisms may be detected by molecular biology techniques, eg polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), using the DNA extracted from blood or saliva samples. Genetic kits specific for this diagnosis are available. The procedure consists of extracting and amplifying DNA from the samples, followed with a hybridisation protocol in a strip. Colored bands are obtained as final result. Depending on the different combination, it would be possible to determine whether the patient is lactose intolerant. This test allows a non-invasive definitive diagnosis.

Management

Pregnancy - About 44% of lactose-intolerant women regain the ability to digest lactose during pregnancy. This might be caused by slow intestinal transit and intestinal flora changes during pregnancy[citation needed].
Live yoghurt cultures - Lactose intolerance can also be managed by ingesting live yoghurt cultures containing Lactobacilli that are able to digest the lactose in other dairy products. This may explain why many South Asians though genetically lactose intolerant are able to consume large quantities of milk without much symptoms of lactose intolerance. Consuming live yoghurt cultures in lassi (a fermented milk drink) is common in the South Asian population.
Avoiding lactose-containing products - Lactose intolerance is not an absolute condition. The reduction in lactase production, and the amount of lactose that can be tolerated varies from person to person. According to the U.S. National Institutes of Health (NIH), "Dietary control of lactose intolerance depends on people learning through trial and error how much lactose they can handle." Affected persons must learn to read and understand food labels.
Minimise occurence and symptoms - Since lactose intolerance poses no further threat to a person's health, the condition is managed by minimizing the occurrence and severity of symptoms. Berdanier and Hargrove recognise four general principles in dealing with lactose intolerance: (i) avoidance of dietary lactose, (ii) substitution to maintain nutrient intake, (iii) regulation of calcium intake and (iv) use of enzyme substitute.