Diagnosis of lactose intolerance and the “nocebo” effect: The role of negative expectations

Abstract Background Diagnosis of lactose intolerance is based on a “positive” H2 breath test associated with abdominal symptoms. The present study established to what extent the occurrence of symptoms during a “negative” H2 breath test may result from a “nocebo effect” instead of lack of sensitivity of the procedure. Methods Between 2005 and 2007, 636 outpatients performed a standard 4-h 25 g lactose tolerance test. The test was positive in 254, negative in 325, and 57 patients were H2 “non-producers”. Twenty-seven patients reporting symptoms despite a negative H2 breath test underwent a “sham” breath test following ingestion of 1 g of glucose. Fifty-four patients presenting with documented lactose intolerance were used as controls. Results Twelve out of 27 patients (44.4%), and unexpectedly also 14 (25.9%) controls presented abdominal symptoms during the sham test. The difference between the two groups was not significant ( P < 0.15) OR 2.28; C.I. 0.77–6.78. Conclusion In most instances, symptoms reported by patients during a negative lactose H2 BT cannot be attributed to a false-negative test. Instead, a non-organic component, resulting from negative expectations (“nocebo effect”) is likely implicated. Moreover, also in patients diagnosed as lactose intolerant, the need for restricting the primary source of dietary calcium should be critically reconsidered.