Lactose intolerance and health.

OBJECTIVES: We systematically reviewed evidence to determine lactose intolerance (LI) prevalence, bone health after dairy-exclusion diets, tolerable dose of lactose in subjects with diagnosed LI, and management. DATA SOURCES: We searched multiple electronic databases for original studies published in English from 1967-November 2009. REVIEW METHODS: We extracted patient and study characteristics using author's definitions of LI and lactose malabsorption. We compared outcomes in relation to diagnostic tests, including lactose challenge, intestinal biopsies of lactase enzyme levels, genetic tests, and symptoms. Fractures, bone mineral content (BMC) and bone mineral density (BMD) were compared in categories of lactose intake. Reported symptoms, lactose dose and formulation, timing of lactose ingestion, and co-ingested food were analyzed in association with tolerability of lactose. Symptoms were compared after administration of probiotics, enzyme replacements, lactose-reduced milk and increasing lactose load. RESULTS: Prevalence was reported in 54 primarily nonpopulation based studies (15 from the United States). Studies did not directly assess LI and subjects were highly selected. LI magnitude was very low in children and remained low into adulthood among individuals of Northern European descent. For African American, Hispanic, Asian, and American Indian populations LI rates may be 50 percent higher in late childhood and adulthood. Small doses of lactose were well tolerated in most populations. Low level evidence from 55 observational studies of 223,336 subjects indicated that low milk consumers may have increased fracture risk. Strength and significance varied depended on exposure definitions. Low level evidence from randomized controlled trials (RCTs) of children (seven RCTs) and adult women (two RCTs) with low lactose intake indicated that dairy interventions may improve BMC in select populations. Most individuals with LI can tolerate up to 12 grams of lactose, though symptoms became more prominent at doses above 12 grams and appreciable after 24 grams of lactose; 50 grams induced symptoms in the vast majority. A daily divided dose of 24 grams was generally tolerated. We found insufficient evidence that use of lactose reduced solution/milk, with lactose content of 0-2 grams, compared to a lactose dose of greater than 12 grams, reduced symptoms of lactose intolerance. Evidence was insufficient for probiotics (eight RCTs), colonic adaptation (two RCTs) or varying lactose doses (three RCTs) or other agents (one RCT). Inclusion criteria, interventions, and outcomes were variable. Yogurt and probiotic types studied were variable and results either showed no difference in symptom scores or small differences in symptoms that may be of low clinical relevance. CONCLUSIONS: There are race and age differences in LI prevalence. Evidence is insufficient to accurately assess U.S. population prevalence of LI. Children with low lactose intake may have beneficial bone outcomes from dairy interventions. There was evidence that most individuals with presumed LI or LM can tolerate 12-15 grams of lactose (approximately 1 cup of milk). There was insufficient evidence regarding effectiveness for all evaluated agents. Additional research is needed to determine LI treatment effectiveness.