Lactose and milk intolerance: clinical implications.

We studied 166 hospitalized male patients to determine the clinical importance of tolerance-test-determined "lactose intolerance," assumed to affect most of the world's adults. Abnormal lactose tolerance tests were found in 81% of 98 blacks, 12% of 59 whites of Scandinavian or Northwestern European extraction, and three of nine non-European whites. Seventy-two per cent of the "lactose-intolerant" subjects had previously realized that milk drinking could induce abdominal and bowel symptoms. Two hundred and forty milliliters of low-fat milk produced gaseousness or cramps in 59% of 44 "lactose-intolerant" men, and 68% were symptomatic with the equivalent amount of lactose. None of 18 "lactose-tolerant" men noted symptoms with milk or lactose. Refusal to drink 240 ml of low-fat milk served with meals correlated significantly with "lactose-intolerance": 31.4% versus 12.9% among "lactose-tolerant" patients. "Lactose intolerance" is common in adults and is a clinically relevant problem.