Study Finds Most Lactose Intolerant People Can Drink Milk
BOSTON (AP) _ Can a single glass of milk cause gas, cramps and bloating? Millions of Americans think so, but a new study of lactose intolerance concludes they’re wrong.
``The final result is, there is virtually nobody out there who cannot tolerate a glass of milk a day,″ said Dr. Michael D. Levitt, the study’s senior author.
Those who blame milk for their digestive ills are likely to be surprised and dubious. About one-quarter of people in the United States, and three-quarters worldwide, are lactose intolerant. They lack an enzyme that allows them to digest lactose, the sugar in milk.
Drinking large amounts of milk, such as a liter at one sitting, will almost certainly cause intestinal misery for these people. But many claim tiny amounts cause problems. They say they cannot even put milk on cereal or in coffee.
To test this idea, Levitt and colleagues at the Veterans Affairs Medical Center in Minneapolis posted ads to recruit people who thought they were severely lactose intolerant. They complained of abdominal pain, bloating, flatulence or diarrhea after drinking milk.
First, the researchers tested 30 volunteers to see if they were truly lactose intolerant. A simple breath test revealed that 21 actually were. The nine others could digest lactose, despite their beliefs to the contrary.
Next, all 30 were assigned to drink an 8-ounce glass of milk with breakfast. For one week, they got milk that was treated with the enzyme lactase to break down the milk sugar. For another week, they got ordinary milk that was slightly sweetened to taste like the treated milk. Neither the researchers nor the volunteers knew which they were drinking.
The volunteers rated their intestinal discomfort each week on a scale of 0 to 5. When the experiment was over, there was no difference. On both kinds of milk, the scores averaged less than one.
Levitt published his findings in Thursday’s issue of the New England Journal of Medicine.
``A lot of people won’t believe this study,″ he said. ``Some are awfully wedded to the idea that a drop of lactose will give them symptoms.″
Lactase manufacturers were also skeptical. At Schwarz Pharma, which makes Lactrase capsules for the lactose-intolerant, chemist Mary Anne Krupski questioned whether other foods the volunteers ate could have helped minimize their symptoms.
``It does prove there are a lot of people out there who think they are lactose intolerance and aren’t, but it doesn’t prove anything about whether lactase products work,″ she said.
Why do people blame their cramps and gas on milk? Levitt said one reason may simply be the pervasiveness of news stories about lactose intolerance and advertising for products to counteract the problem. Such products include chewable tablets, milk additives and specially processed milk.
If someone feels bloated after dinner and then reads that milk can do this, Levitt said, it is easy to make the assumption he has found the cause.
An editorial in the journal said some people may search for medical causes for occasional unpleasant sensations that others simply ignore.
``Lactose intolerance is an example of an intestinal ailment that may be blamed for abdominal symptoms that either are normal sensations or have other causes,″ wrote Dr. Juan-R. Malagelada of Hospital General Vall d’Hebron in Barcelona, Spain.
A built-in backup system helps the body deal with modest amounts of milk sugar, even when there is no enzyme to help out.
When lactose is not broken down during digestion, it passes into the large intestine. There, bacteria ferment the sugar, producing fatty acids and hydrogen gas.
The gas is quickly consumed by bacteria or absorbed into the bloodstream. Bloating and flatulence result only when people drink so much milk that they overwhelm this disposal mechanism.
Surveys in North America suggest that 21 percent of white people are lactose intolerant, as are 79 percent of Indians, 75 percent of blacks and 51 percent of Hispanics.