Milk Does a (Rat's) Body Good

It turns out it really does matter whether you've 'got milk.'
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Researchers from Purdue University have shown that dairy is better than calcium carbonate — the most common form of calcium used in foods and supplements — at promoting bone growth and strength. In a study, the bones of rats fed nonfat dry milk were longer, wider, stronger and had more density than those of rats on a diet of calcium carbonate.

The results should perhaps be taken with a grain of salt (or a sip of milk) because the study was funded by the National Dairy Council. But it's the first direct comparison of the impact on bone structure from calcium in supplements and milk, and the research appears online in the Journal of Bone and Mineral Research.

"A lot of companies say, 'If you don't drink milk, then take our calcium pills or calcium-fortified food,'" said Connie Weaver, distinguished professor and head of Purdue's food and nutrition department, in a press release announcing the findings. "There's been no study designed properly to compare bone growth from supplements and milk or dairy to see if it has the same effect."

The Purdue study involved 300 rats, split up into two groups. For 10 weeks, the rats were given all their required nutrients, but one group got its calcium through dairy and the other through calcium carbonate. After 10 weeks, the bones of 50 rats from each group were evaluated for strength, density, length and weight. The rats that had milk instead of calcium carbonate had measurements up to 8 percent higher in these categories.

A second part of the study also discovered a strong effect from having dairy as a source of calcium even when followed by periods of inadequate intake.

"This is comparable to humans who, during their early growth, drink a lot of milk to the age of 9 to 11, or maybe even adolescence, but then get only half as much milk calcium as they need after that," Weaver said. "Some take calcium supplements, but few adults get adequate calcium. ... We found it was an advantage having milk or dairy while bones were growing over calcium carbonate, and it protects you later in life."

Weaver added that she is not sure, exactly, why dairy is better for bone properties, and called for further study. "I think this will spark some people to want to figure out what it is about milk that gives it an advantage," she said.

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