For years we've been told that teenagers should drink three glasses of milk a day or the equivalent in dairy foods to build up bone reserves that help prevent osteoporosis and bone fractures later in life. But a comprehensive new study throwing this conventional wisdom into serious question.
The research, which appears in Monday's issue of the Journal JAMA Pediatrics, considered the longterm effects of drinking milk among more than 61,000 women and 35,000 men over the course of 22 years. The purpose of the study was to determine whether milk consumption during adolescence influences risk of hip fracture in older adults.
During the follow-up, a research team led by Harvard Medical School's Diane Feskanich documented 1,226 hip fractures in women and 490 in men. More than 90% of the fractures were the result of tripping or falling from a chair.
After taking various risk factors into consideration, as well as ongoing milk consumption, the research team had no choice but to conclude that: "Greater milk consumption during teenage years was not associated with a lower risk of hip fracture in older adults."
For the women (all of whom were white and post-menopausal), no positive link could be established. But for men, each additional glass of milk per day during teenage years was associated with a 9% increased risk of hip fractures! The researchers attributed this, in part, to the fact that males tend to be taller than women — a known risk factor for fractures.
"It does make you stop and ponder and want to see better evidence for our dietary recommendations," Feskanich said of the study's findings.
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The study's authors noted it isn't calcium alone in milk that contributes to bone development. Fortified milk is a good source of vitamin D, which is important for strengthening bones around puberty, and also contributes protein and other nutrients.
Weight-bearing activities that are done on your feet and work against gravity are also recommended for bone health at all ages.
One of the study's limitations is the potential for error from asking participants to recall their milk consumption during their teenage years. The researchers didn't ask about preteen consumption but said that could be more relevant for females since girls reach their peak height about two years before boys.
It's important to note that the researchers aren't saying that you should stop drinking milk. Just don't expect the health benefits to match the hype.