You’ve written about calcium, protein, and bone health a number of times and you always seem to stress that it’s important for vegans to get the RDA for calcium. Most of what I’ve read about vegan diets shows that we don’t need to worry about calcium. You ignore the fact that, in cultures where people eat very low protein diets, they don’t have osteoporosis even though they have very low calcium intakes. Since protein causes osteoporosis, and vegans eat a low protein diet, vegans have low calcium needs.

Well, first of all, it is not actually a fact that people don’t have osteoporosis in those cultures. What is a fact is that we see a smaller incidence of hip fractures in those cultures. And you are right, I do ignore this, because it turns out that it is not especially useful information for western vegans.

The idea that vegans do not need to worry about calcium is based on the fact that, world wide, there is no relationship between the incidence of hip fractures and intake of calcium. There does seem to be a relationship between hip fractures and protein intake, however, with hip fracture rates rising in countries where protein intake is high (like the United States). There are also laboratory studies showing that high protein intake negatively impacts bones. As a result, many vegans believe that they have low calcium needs because they have low protein intakes. But this is actually a very simplistic interpretation of an extremely complex health issue. Although I’ve written about the relationship between protein and calcium before, I haven’t written much about the hip fracture data, so let me try to pull all of this information together here.

First, when we try to make comparisons of bone health in different countries based strictly on rates of hip fractures, we are on rather shaky ground. This is because, among different cultures, hip fracture rates are affected by much more than diet. Here are some of the factors that affect hip fractures:

1. Culture: The leading cause of a hip fracture is falling. That is, if you have two people who both have osteoporosis, the one who falls is the one who is going to break a hip. It is possible that people fall more in some cultures than in others. For example, in some Asian cultures, older people do not often go out by themselves. They are part of an extended family and are often with an adult child when they are away from home. This kind of support would greatly reduce the risk of falling. People in these cultures may also eat a lower protein diet. But if they simply fall less, how can we say that their reduced hip fracture rate is related to their diet rather than their lifestyle?
2. Geography: Again, this is related to falling. People who live in warmer climates–where there is less snow and ice on the ground–are less likely to slip and break a hip.
3. Genetics: This is especially important because it is less speculative than the two factors I noted above. The hip bone in Asians is shorter than in other groups and is more resistant to breakage. This has nothing to do with diet and lifestyle; it is purely a genetic factor. Also, some people, particularly those of African background, metabolize calcium differently and have a genetic predisposition to denser bones.

It’s easy to see that you can’t look at hip fracture rates in different cultures and make a conclusion about diet. There are too many other factors at work here. So it shouldn’t be too much of a surprise to learn that, in some countries where hip fracture rates are low, people still have considerable osteoporosis, in their spine for example.

Therefore, it just is not possible to draw any conclusions about bone health based on comparisons of hip fracture rates. It is also impossible to determine vegan calcium needs based on these hip fracture observations.

Certainly, the relationship of protein to calcium is important. Diets high in protein, particularly high in meat protein, can cause excessive calcium losses. Protein increases the acidic condition of the body, and the reaction in the body that neutralizes that acid results in loss of calcium from bones. It’s normal to lose some calcium since bones are dynamic and are always turning over. But anything that raises the rate of calcium loss will also raise calcium needs. But this is probably much less important when calcium intake is high. It’s only when calcium intake is low that protein appears to have an important effect on bone health. And it may also be that it isn’t so much the total amount of protein in your diet that matters, but the ratio of protein to calcium. Vegans actually have a ratio that is too high since, although their diets are lower in protein, they are also often lower in calcium. (With the growing number of calcium enriched foods for vegans on the market, however, this may change).

Also, while too much protein may be harmful to bones, so is too little protein. Studies show that among western women, protein is linked to better bone health. And protein supplements have been shown to speed healing of fractures. Although it isn’t very difficult to get adequate protein on a vegan diet, some vegan women–especially those who eat low calorie diets–may have protein intakes that are marginal.

In addition, there is some evidence that vegan women have lower blood levels of estrogen. Since estrogen strengthens bones, these lower levels may actually counter any positive effects of a more moderate protein intake. Some vegans also have low levels of vitamin D in their blood, which would increase risk for osteoporosis.

None of this is to say that vegans are actually at higher risk for osteoporosis. The point is that we have no good evidence that they are at lower risk. It’s possible that eating a vegan diet does lower calcium needs–but we don’t know that yet. So until then, it’s important for vegans to meet the RDA for calcium, which is 1,000 mg for adults. For information on how to get enough calcium on a vegan diet see my article from November 20, 2000.

Of course, it still makes sense to eat a vegan diet. The foods that provide calcium to vegans are far more healthful than dairy products. In addition, plant foods provide other compounds that may enhance bone health. For example, leafy green vegetables provide calcium and they also provide vitamin K, which may be important for bone health. Many soyfoods provide both calcium and isoflavones, compounds that may help maintain the health of bones. Calcium-fortified orange juice contains vitamin C which is needed for healthy bones. And of course, plant foods are rich in all types of compounds that protect against other diseases.