Vegan for Life - Jack Norris [19]
Osteoporosis is a crippling and debilitating disease of severe bone loss—as much as 30 to 40 percent of total bone—that affects an estimated 10 million Americans. Eighty percent of Americans with osteoporosis are women.
When nutrition scientists look at the relationship of diet to bone health, they look at both bone density and fracture rates. And the findings are anything but clear. How much calcium humans need and the extent to which varying intakes affect bone health are topics of intense research. Many large epidemiologic studies fail to show that high calcium intakes protect against bone fractures. 3,4 The balance of evidence suggests, however, that calcium and vitamin D together are protective.5
Protein and Calcium: More Questions than Answers
A couple of decades ago, studies of bone health among people in different countries revealed an interesting pattern. Rates of hip fracture (which is often used as a marker for bone health) were highest in countries with the highest intakes of animal protein, even though calcium intake was also high.6 The findings suggested that too much protein was worse for bones than too little calcium. And, in fact, there is a biological explanation to back this.
High intakes of certain proteins increase the blood’s acidity, kicking off a chain of reactions to bring blood back to a more neutral pH. A release of calcium from the bones is one part of the process. The more acidic the blood, the greater the loss of calcium from bones. Meat proteins are among the most acid-producing foods, followed by proteins from grains and dairy. Diets high in fruits and vegetables are the least acidic.
Based on this, it seems to make sense that people who eat animal protein should need more calcium to replace what is constantly being leached from their bones. Conversely, wouldn’t vegans, whose diets contain no animal proteins, have lower calcium needs? This sounds like an obvious conclusion, but it’s not quite that straightforward.
First, the studies comparing different populations have limited usefulness. These are ecological studies, and we saw in Chapter 1 that they provide only weak evidence. There are just too many cultural and genetic variations among people of Asian, African, and Caucasian backgrounds for us to make direct comparisons about their protein intakes and bone health. For example, people of African descent have a genetic predisposition toward stronger, heavier bones.7 And a slight genetic advantage in hip anatomy among Asians protects against fracture.8
There are cultural differences too. Asians tend to have better balance, so they are less likely to fall and break a bone. And in some cultures, elderly people rarely leave their home without a younger family member at their side and are therefore less likely to fall. In fact, while Asian populations fare well in comparisons of hip-fracture rates, their spinal bone health is similar to westerners’.9 This suggests that there is something in their genes or lifestyle that is specifically protective against hip fracture but doesn’t affect other parts of the skeleton. If diet were the protective factor, the benefits would show up in all parts of the skeleton.
As a result, these cross-cultural studies might tell us more about culture and genetics than about diet, which means that these comparisons don’t tell us a whole lot about how much calcium western vegans might need.
It’s better to look at clinical research, where the