After 13 years of scouring the human genome for the basis of lactose intolerance — the inability to digest the milk protein lactose — researchers have finally identified a genetic cause. Researchers anticipate the results will lead to improved diagnostic tests for the condition.
For about 50 million Americans, a snack of milk and cookies causes nausea, cramps, bloating, gas and diarrhea within 30 minutes to 2 hours of chugging back the last drop. What causes this discomfort? The simple answer: “lactase deficiency.” Ironically, what sounds like a disorder, may actually be normal.
Lactase is an enzyme that allows the body to process lactose. In most humans, the lactase gene is active at birth but becomes inactive after weaning. As a result, the body produces less lactase, and eating milk products becomes a pain in the gut. As many as 75 percent of all African-Americans and Native Americans, and 90 percent of Asians are lactose intolerant; only 15 percent of people of European descent are lactose intolerant.
Researchers have spent over a decade analyzing the lactase gene for mutations and have failed to see any differences between people who can digest lactose and those who cannot. It turns out they’ve been looking at the wrong piece of DNA.
Leena Peltonen and her colleagues studied a section of DNA that lies near the lactase gene in nine Finnish families with a history of lactose intolerance. Their study revealed two separate single-unit DNA changes in the DNA of all the lactose intolerant family members. The group then looked for the genetic variation in lactose-intolerant adults of European, African-American and Asian descent, and found the same variation, an unexpected event in such divergent ethnic groups.
“The only explanation is that this DNA variant is old,” says Peltonen. “The findings suggest that this is the original form of the gene, and that it must have been in the human genome when the human species began to migrate out of Africa.”
Some biologists believe that during the development of the dairy culture 10,000 years ago, some people acquired a mutation that allowed them to digest lactose into their adult years. If true, this hypothesis could explain why most Europeans tolerate milk products.
Peltonen says that although the study hasn’t uncovered the molecular mechanism behind lactose intolerance, the results provide researchers with a tool for future studies and the development of a diagnostic test. A highly accurate test, she says, could be done on a single drop of blood.
Today, lactose intolerance is diagnosed using a lactose tolerance test, which measures the amount of digested lactose in the blood after the patient drinks a lactose-rich liquid, or using a hydrogen breath test, which measures the amount of hydrogen produced by gut bacteria who feed on undigested lactose. A genetic diagnostic tool would benefit very young children and infants suspected of lactose intolerance because conventional tests are too dangerous for them.
There is no treatment for lactose intolerance, but by adopting a lactose-free diet sufferers can control symptoms. Most lactose intolerant people learn early in life how much lactose they can tolerate. Some can enjoy milk and cookies once in a while; others might be able to eat cheddar, but not drink milk. “It’s important that people realize that some of them can eat cheese, while others can’t,” says Royletta Romain, campus dietician at Boston University. Some aged cheeses, like cheddar and Swiss, actually contain very little lactose because manufacturing removes most of the lactose. Similarly, lactase-deficient people may be able to eat yogurts with “live active cultures” because the bacterial cultures partially digest the lactose.
People who can tolerate some lactose can take lactase enzymes such as Lactaid when they eat dairy products, and a caffeine fix can be topped with milky froth if it’s made from a lactose-free milk or soy milk. While switching milk for soy milk at Starbucks may cost you an extra 25 cents, a box of Extra-Strength Lactaid (44 tablets) will set you back about four-and-a-half dollars, and a half gallon of Lactaid fat-free milk costs $3.
Besides calcium, there are nine other essential nutrients in milk, all of which are important to a healthy diet, says Serena Ball, a registered dietician and spokesperson for the National Dairy Council.
“If you’re not able to drink milk or digest cheese,” says Romain, “you will have issues.” Romain adds that when people cut dairy products out of their diets, many don’t try to get calcium from other sources. “You have to figure out how to get the calcium and those other vitamins,” she says, because they are important to bone strength, and deficiencies can lead to fractures and dry hair and skin.
Ball says people should avoid dairy-free diets and should try to consume small amounts of dairy on a regular basis. “It’s kind of a use it or lose it sort of thing,” she says. “Keeping dairy in your diet may allow you to hang on to the ability to digest it.” Rather than offering a one-size-fits-all solution, Romain favors a client-by-client approach, addressing students’ dietary concerns individually and “determining if they need a calcium supplement.”
The BU perspective
Statistically speaking, nearly a quarter of the 4,132 first-year students who enrolled at BU in 2000 may have been lactose intolerant. However, Romain says that only five or 10 students approach her each year about lactose intolerance. “I’m sure there are many I don’t know about though,” she adds.
Choosing meals from the vegan stations in dining halls is another way to stay lactose free. Vegan options, “definitely won’t have any milk or dairy products in them,” says Romain
Steve Canario, dining services operations director, says the school accommodates students with nutritional concerns by providing them with alternate menus.
“In terms of menu selection, there is a wide array in the GSU or the residence halls that are lactose free. We offer soy milk and Lactaid in all of the residences,” says Canario. Although avoiding dairy products may seem simple enough, many meats and processed foods contain lactose or whey. Derived from milk, whey helps spices stick to many processed foods. Lactose intolerant people should check the nutrition labels on canned tuna and salmon, seasoned French fries and Butterball turkey. “You wouldn’t think that onion rings have whey in them,” says Romain, “but they do.”
This is an account occasionally used by the Daily Free Press editors to post archived posts from previous iterations of the site or otherwise for special circumstance publications. See authorship info on the byline at the top of the page.
