Why Do People Become Lactose-Intolerant?

Most of us drank milk every day when we were young without a problem. Then,
sometime in our teens or early 20s, we start to feel bloated or have discomfort
after consuming a lot of milk, typically two or more glasses at a time.

Scientists have discovered that most people develop some degree of lactose
intolerance as they get older. Why we lose this ability to break down lactose,
the key sugar found in milk, is a puzzle that researchers have been trying to
figure out. The National Institute of Child Health and Human Development, part
of the National Institutes of Health, will hold its first conference on the
topic next week.

It is unusual for people to lose the ability to digest a nutrient as they age.
But most people stop making large quantities of "lactase"the enzyme that breaks
down lactoseafter childhood, says Eric Sibley, an associate professor of
pediatrics at the Stanford University School of Medicine, who has been studying
why people develop lactose intolerance as they get older.

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