Lactose intolerance in patients with irritable bowel syndrome from northern India: A case-control study

Background and Aim: Symptoms of irritable bowel syndrome (IBS) and lactose intolerance (LI) overlap. Data on the frequency of LI in patients with IBS from India are scanty. The aim of this study was to evaluate: (i) the frequency of LI in patients with IBS and its various subtypes as compared with healthy subjects (HS) from northern India; (ii) the relationship between self-reported milk intolerance and laboratory evidence of LI; and (iii) the role of small intestinal bacterial overgrowth in LI in patients with IBS. Methods: 124 patients with IBS (Rome II criteria) and 53 age- and gender-matched HS were studied for LI using the lactose hydrogen breath test (LHBT) and the lactose tolerance test (LTT). Symptoms following lactose ingestion (diarrhea, bloating or distension) during the test and history of milk intolerance were recorded. Sixty-nine of the patients with IBS also underwent a glucose hydrogen breath test (GHBT). Patients with IBS were classified into those with diarrhea (IBS-D; > 3 loose stools/d), constipation predominant (IBS-C; < 3 stools/week) and indeterminate (IBS-I; between >= 3/week and <= 3/d). Results: 89/124 (72%) and 32/53 (60%, P = ns) IBS patients and HS were positive by LHBT and 82/124 (66%) and 38/53 (71%, P = ns) by LTT. Lactose intolerance as diagnosed either by LHBT or LTT was comparable among IBS patients and HS (102/124, 82% vs 41/53, 77%; P = ns). Peak breath hydrogen values during LHBT were also comparable among patients with IBS and HS (64 +/- 40 p.p.m. vs 61 +/- 44 p.p.m.). Patients with IBS developed symptoms following lactose ingestion more frequently than HS (68/124 vs 18/53, P = 0.01). Glucose hydrogen breath test was positive in 9/69 (13%) patients with IBS and was comparable among patients with (8/57, 14%) and without LI (1/12, 8%). Thirty had IBS-D whereas 94 had other subtypes of IBS (IBS-C, n = 9 and IBS-I, n = 85). The frequency of LI in IBS-D was similar to that of other subtypes (26/30, 86% vs 76/94, 80%; P = ns). The positive and negative predictive value of self-reported milk intolerance in detecting LI was 81% and 23%, respectively. Conclusion: The frequency of LI is high and comparable among IBS patients and HS from northern India. Patients with IBS more often reported symptoms following lactose ingestion despite levels of breath hydrogen being similar to HS. The frequency of LI in patients with IBS-D was comparable to that in patients with other types of IBS. Self-reported milk intolerance has poor sensitivity in detecting LI.