The federal government's dietary guidelines urge adults to consume at least three cups of milk a day to guard against osteoporosis, a disease in which bones become brittle and weak. People who are lactose intolerant—a group that includes 75 percent of African Americans—"can choose low-lactose and lactose-free dairy products," the guidelines say. But a new study has called into question this one-size-fits-all approach. It suggests that most African American adults might not need milk at all.
Scientists have known for some time that people who live in Africa have some of the world's lowest rates of osteoporosis. Researchers long assumed that the difference was due to Africans' lower life expectancy (since the condition usually shows up later in life), more active lifestyles, and a lack of doctors to diagnose and treat the condition. Yet a study published in June in BoneKEy, an offshoot of the journal Nature, offers a compelling alternative explanation: Many Africans are genetically adapted to low-calcium diets.