Like most things that make good headlines, the actual research is much more subtly nuanced and I recommend you read the entire article. At the risk of getting in trouble, I’m going to paste the whole thing here, because you’d have to scroll down the article past a bunch of stuff about cholesterol and heart health to get to the bone stuff, which might lead you to think I posted the wrong link. (But in case you want to read about the entire China Study debunking, here’s the link.) Thank you, Betsy, for bringing this to my attention. Fascinating!
Dietary calcium and bone density among middle-aged and elderly women in China (PDF) by Ji-Fan Hu, Xi-He Zhao, Jian-Bin Jia, Banoo Parpia, and T. Colin Campbell.
True to its title, this paper examines the role of calcium in bone density in the China Study data—with a special focus on the effects of dairy calcium versus plant calcium. Campbell et al. zoomed in on five counties with “distinct lifestyles and diets”: the dairy-and-meat-loving Xianghuangqi, the infamous dairy-full Tuoli, and the rural, nearly-vegan farming towns of Jiexiu, Cangxi, and Changle.
But before we look at the paper itself, let’s see how Campbell summarized its findings in a Cornell Chronicle article in 1994:
Animal protein, including that from dairy products, may leach more calcium from the bones than is ingested, said Campbell, professor of nutritional biochemistry at Cornell and director of the Cornell-China-Oxford Project, the most comprehensive project on diet and disease ever conducted.
Campbell [and other collaborators] analyzed the role of dietary calcium in bone density by following closely the diets of 800 women from five counties that have very different diets in China. … Analyses of these data suggest that increased levels of animal-based proteins, including protein from dairy products, “almost certainly contribute to a significant loss of bone calcium while vegetable-based diets clearly protect against bone loss,” Campbell reported.
Sounds pretty clear: The dairy-eating counties must have had poor bone health due to their animal protein habit, whereas the more plant-based dieters were skeletally superb. In other words, milk does a body bad! But do the summaries above match up with this paper actually found? First, let’s look at what the women in each county were typically eating:
*Lest I get the “you’re trying to justify your dairy addiction” line and/or accusations of dairy industry affiliation, I’d like to remind everyone that dairy hasn’t been part of my diet in over six years, and I believe the dairy most people consume (low-fat, ultra-pasteurized, etc.) is downright nasty stuff. But that doesn’t mean I won’t defend dairy when the science warrants it.
As you can see, Xianghuangqi ate a pretty shabby diet as far as whole-foods veganism is concerned: We’ve got dairy galore, beef, mutton, wheat flour, a mere smattering vegetables, and millet. Their bones should be snapping like peanut brittle! Tuoli’s not much better, what with their milk tea, animal flesh, and decided lack of green leafy veggies. More bone snappage, right?
I’ll let the paper speak for itself:
Analysis by individual for all counties combined showed that [bone mineral content] and [bone mineral density] were correlated positively with total calcium (r = 0.27-0.38, P < 0.0001), dairy calcium (r = 0.34-0.40, P < 0.0001), and to a lesser extent with nondairy calcium (r = 0.06-0.12. P = 0.001-0.100), even after age and/or body weight were adjusted for. The results strongly indicated that dietary calcium, especially from dairy sources, increased bone mass in middle-aged and elderly women by facilitating optimal peak bone mass earlier in life.
Did you catch that? Dairy calcium—far more than plant calcium—was linked with stronger bones. Moreover, the paper notes that “nondairy calcium … showed no association with bone variables after age and/or body weight were adjusted for.”
Comparison of results in Table 7 reveal that calcium from dairy sources was correlated with bone variables to a higher degree than was calcium from the nondairy sources, probably resulting from the higher bioavailability of dairy calcium.
A comparison of the bone mass of women in the five counties revealed that 20% greater bone mass at the distal radius was observed for all age groups of women in county YA [Xianghuangqi], a pastoral county with high consumption of dairy foods, as compared with the nonpastoral areas with lower calcium intakes.
I’ll add my own unsolicited 2¢ and speculate that calcium probably wasn’t the only protective factor in the dairy-eating counties. Aged cheese, likely consumed at least in Xianghuangqi, is high in vitamin K2—a nutritional superstar when it comes to bone health (among other things). K2 isn’t present in plant foods except for a fermented soy product called natto (not everyone’s cup o’ tea). As the paper notes, the dairy-eating counties also had a higher intake of fat (25% of daily calories, opposed to 9.9 – 13.6% for the other counties), potentially increasing the absorption of fat-soluble vitamins necessary for bone health.
So how did Campbell conclude from this study that “increased levels of animal-based proteins, including protein from dairy products, almost certainly contribute to a significant loss of bone calcium”? The dairy part is unfounded no matter which way you spin it, but the rest of his statement probably stemmed from this:
The associations between bone mass and other nutrients, like dietary protein and phosphorous, were also examined. However, none of these nutrients showed an association with bone mass as significantly as did dietary calcium, although an inverse correlation was observed consistently for nondairy animal protein.
Unfortunately, that’s the only blurb in the entire paper that mentions animal protein in relation to bone mass, so we can’t see the data behind the “consistent inverse correlation.” In the context of this study, though, it makes sense: Protein has a complex relationship with bone formation, serving as a synergist when calcium intake is adequate, but as a potential antagonist when calcium intake is low. In other words, the effects of protein on bone health depend on how much calcium you’re taking in.
So for the counties in this study that ate more animal protein but sparse calcium—such as Changle, which had the highest non-dairy animal food consumption and also the lowest calcium intake (averaging a mere 230 mg per day)—I wouldn’t be surprised if an animal protein/weaker bones connection showed up. Whether that trend would hold at higher calcium intakes is a different story. And either way, this finding doesn’t jive with most other research done on this topic: Most studies show a protective association between animal protein and bone density, formation, and retention:
In addition, if animal protein was such a bone-killer and plant protein was bone protective, we’d see vegetarians or vegans having the best outcomes in the bone department. But this just ain’t the case. At best, non-meat-eaters are equally matched with their omnivorous counterparts; at worst, they’re more prone to fracture:
So, although the “calcium-leeching” properties of animal protein is a common battle cry in the vegan world, the research just doesn’t support it. There are even some interesting (and peer-reviewed!) papers out there looking at how belief systems influence the interpretation and misrepresentation of bone/protein studies. Read that link because it’s awesome.
But back on topic. This paper, with Campbell’s own name on it, suggests a strongly bone-protective role for dairy in the diet. Not quite the message we heard in “The China Study.”
So that’s a lot of food for thought. In some ways it makes me sad — I’d like to think avoiding certain foods is the magic bullet for my weak bones. In other ways it makes me happy. I can enjoy my mac-n-cheese in peace.