Q. Why do some people become lactose intolerant as they age?
A. All of us are born with the ability to make an enzyme called lactase, which helps our small intestines digest the otherwise unwieldy sugar lactose found in milk. Many people’s lactase levels decline when they’re a few years old, a hardwired phenomenon that depends on a person’s genetic background — most Northern Europeans maintain their lactase levels while most people of African and Asian descent don’t. “Most of the world’s population has low lactase levels as adults — this is definitely not a disease,” says Richard Grand, a gastroenterologist at Boston Children’s Hospital.
Once your lactase levels are set in childhood, they don’t seem to change as you age. But Grand explains that lactose intolerance — bloating, cramping, gas, or diarrhea after consuming milk products — is more complex. “There are multiple reasons for someone to have symptoms of lactose intolerance that are not due to lactose,” he says. The culprit may be fast movement of food through the digestive system that’s caused by other foods the lactose is eaten with, or by a genetic predisposition. Digestion can also slow down or speed up with age, which is why people notice more digestive disturbances as they get older.
Grand says that many people with low lactase can still digest some milk because bacteria in their large intestines take over the task of digesting lactose. For those who feel they truly can’t digest it, he recommends calcium and vitamin D supplements to prevent deficiencies.