Quite a few popular vegan websites and books make the claim that vegans don’t need as much calcium as omnivores. The theory dates to some interesting research from the early 1990s which found that hip fracture rates among different countries increased as per capita protein intake went up.
The observations were backed by decades of clinical studies, too. As far back as the 1920s, nutritionists were showing that feeding meat to subjects caused them to excrete more calcium in their urine. Theoretically, this is because protein has an acidifying effect on the blood. Calcium is leached from the bones as part of the process that neutralizes blood and restores its normal pH.
Calcium is released from the bones and excreted in the urine all of the time anyway; bones are dynamic and are constantly breaking down and rebuilding. That’s why we need to consume calcium even when bones aren’t growing. But anything that speeds up calcium loss—like a diet high in animal protein—might make it hard to consume enough dietary calcium to rebuild bones.
So, rather than a disease of calcium deficiency, it started to look like osteoporosis was a disease of excess—too much animal protein. And it seemed logical that vegans, who don’t consume any animal protein, would lose less calcium and therefore need less in their diet.
End of story? Well, unfortunately, not quite.
The studies comparing hip fracture rates among countries were ecological studies. They show interesting associations but, given the many variables among different countries and cultures, it’s hard to draw real conclusions. For example, Asians have a slightly different hip structure than other ethnic groups which makes it more resistant to fracture. That might explain why Asians have fewer hip fractures than westerners but have similar rates of spinal fractures and also similar bone density.
There are also geographic and cultural explanations for the differences in hip fracture rates. Falling is a big cause of hip fracture and for a number of reasons, Asians fall less often than Westerners. The comparison also doesn’t control for physical activity, which is very protective of bone health, or for childbearing. Women in some of the countries in the comparisons have many more pregnancies than westerners, and there is some evidence that pregnancy improves bone health (although not all studies agree about that).
Recent clinical trials have also cast doubt on the theory. It’s true that protein can increase bone turnover, but it also appears to increase calcium absorption from food. Some research suggests that the increased absorption could easily compensate for the calcium lost from the skeleton. A number of studies have shown that higher protein intake has a positive effect on bone health when calcium intake is adequate but not when calcium intake is low.
The research findings are not in 100% agreement but for the most part, they just aren’t supportive of a lower calcium recommendation for vegans. That can be kind of discouraging, I know, but vegans need to know where we really stand regarding calcium needs. It’s unfortunate that some activists continue to promote the myth of lower calcium needs as part of their argument for a plant-based diet. Does anyone actually believe that giving vegans inadequate information about calcium helps the cause of veganism and animal rights?
Admittedly, research aimed at identifying the optimal calcium intake for healthy bones is conflicting and confusing. And other aspects of diet that are also very important for bone health often get overlooked. (For example, a diet high in fruits and vegetables appears to be protective for bone health, and vegans may have the edge here.)
But while we may not know exactly how much calcium we need, there is currently no good evidence to suggest that vegans require less than anyone else. This is another situation where basing recommendations on outdated science and wishful thinking just isn’t fair to vegans. And that’s not fair to the animals who depend on us to show how healthy a vegan diet can be.