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 (LM). We assessed the prevalence of LI according to the diagnostic test used, such as 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 self reported dairy intake and diagnosis of lactose intolerance, malabsorption, or lactase deficiency. Reported symptoms, lactose dose and formulation, 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 indicated that low milk consumers may have increased fracture risk, although there was inconsistency in strength and significance depending on exposure definitions. Dietary dairy supplementation in those with low baseline lactose intake did not consistently improve long-term bone health outcomes in children (seven RCTs) or adult women (two RCTs) compared to those not receiving dairy supplementation. Small feeding studies (28 studies) generally demonstrated that a 12 gram dose of lactose (1 cup of milk) produces no or minor symptoms. 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 moderate level evidence that lactase or lactose hydrolyzed milk (28 RCTs) was effective in reducing LI symptoms.
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 have worse bone outcomes compared to children assigned to receive supplemental diary interventions. Many individuals with LI can tolerate up to 24 grams of lactose daily if ingested throughout the day. Lactose reduced milk may be an effective strategy to reduce some LI symptoms. Research is needed to evaluate LI prevalence, bone outcomes in adults in association with lactose intake, genetic predisposition, lactose malabsorption, and intolerance. Studies are needed to determine LI treatment effectiveness.
Lactose Intolerance and Health
Evidence-based Practice Center: Minnesota EPC