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Lactose Intolerance and Health: Consensus from the National Institutes of Health

Definition and prevalence of lactose intolerance

Diarrhea, abdominal pain, flatulence, and/or bloating occurring after lactose ingestion are all symptoms of lactose intolerance syndrome.

Lactose malabsorption occurs due to a decreased ability to digest lactose, caused by a deficiency in the levels of the enzyme lactase. The demonstration of lactose malabsorption does not necessarily indicate that a person will be symptomatic.

Many factors determine whether a person who malabsorbs lactose develops symptoms associated with lactose intolerance. Furthermore, many individuals mistakenly ascribe symptoms of a variety of intestinal disorders to lactose intolerance without undergoing testing.

Lactose intolerance is defined as the onset of gastrointestinal symptoms following a blinded, single-dose challenge of ingested lactose by an individual with lactose malabsorption, which are not observed when the person ingests an indistinguishable placebo.

Based on this definition, the prevalence of lactose intolerance in the United States cannot be estimated, as none of the studies examined used this definition or evaluated a representative sample of the U.S. population.

The studies examined indicate that many individuals predisposed to lactose malabsorption, because of low lactase levels or a genetic profile associated with low lactase, or those demonstrating lactose malabsorption do not experience the onset of or an increase in the severity of gastrointestinal symptoms following a blinded lactose challenge.

Self-reported lactose intolerance is less frequent in all ethnic groups than lactose malabsorption determined by a hydrogen breath test.

Lactose intolerance, lactose malabsorption and lactase non-persistence vary across ethnic groups with the lowest prevalence in European Americans and highest prevalence in African Americans.

Furthermore, current research demonstrates that many who self-report lactose intolerance show no evidence of lactose malabsorption. Thus, the cause of their gastrointestinal symptoms is unlikely to be related to lactose.

Health outcomes of dairy exclusion diets

Many individuals who perceive themselves as having lactose intolerance exclude all dairy from their diets, depriving themselves from a readily accessible source of calcium, vitamin D and other nutrients.

Dairy exclusion diets may exacerbate the risk for osteoporosis for those already at greatest risk. These include women of all ages and certain racial and ethnic groups.

Dairy exclusion diets may affect other health outcomes such as blood pressure control and colon cancer risk, as studies have demonstrated a link between dairy or components such as calcium and a beneficial impact on blood pressure control and reduction in colon cancer risk.

One area of recent interest is the effect of lactose ingestion on colonic bacterial populations, as this may increase production of fatty acids such as butyrate, which may promote mucosal growth and reduce inflammation.

Strategies in managing individuals with diagnosed lactose intolerance

Even in persons with lactose intolerance, ingesting small amounts of milk, yogurt, hard cheeses, and reduced-lactose foods may be tolerated. The limited data available suggest that individuals with lactose malabsorption can ingest up to 12 grams of lactose (the equivalent of 1 cup of milk) without significant symptoms, particularly if they are taken with other foods.

Lactase-treated products may be tolerated better than non-treated products, but more research is needed.

Some strategies such as gradually increasing lactose intake over time, which can result in colonic adaptation, appear promising.

The goals of treatment should be to ensure adequate intake of nutrients important for skeletal health and other clinical outcomes. This is especially important during certain stages of the life cycle when meeting these goals is particularly critical for bone accrual and maintenance, such as during adolescence, pregnancy and lactation, and as people get older.

Keywords: national institutes of health, prevalence, lactose malabsorption

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