Vegan calcium
The calcium requirements for vegans is still undetermined and reamins a point of much discussion. Many dietary and lifestyle factors affect calcium requirements, so vegans, especially those who lead active, healthy lifestyles, may actually have lower needs. One dietary factor that appears to affect the way calcium is used is protein. Diets high in protein may increase calcium needs, because protein causes more calcium to be excreted from the body. This is particularly true of proteins high in certain amino acids, which includes most animal proteins and grains.
Knowing this, it is tempting to assume that vegans - who have lower protein intakes than both omnivores and lacto-ovo vegetarians - have lower calcium needs. While this may indeed by true, there is no real evidence to show that vegans have significantly lower calcium requirements than other groups. Many factors affect calcium needs, and the extent to which protein impacts those needs is not clear (See "Calcium Myths", below).
Because there is no actual evidence that vegans do well with less calcium we must assume - for now - that vegans should strive to meet the recommended daily intakes. There is evidence, however, that lower calcium intake of some vegan women may impair bone health. Studies show that low calcium intake is associated with poor bone health in vegans just as it is in omnivores.
Does this mean that calcium intake is a problem for vegans? Well, certainly some vegan diets are too low in calcium. Studies reveal that a number of vegan women have calcium intakes that are only 400 to 500 milligrams per day while the recommendations are for 1,000 or more milligrams. Any diet can be calcium poor if it isn't well planned. Many omnivore women do not meet calcium needs either. Regardless of how you eat, you need to make sure that your diet includes plenty of calcium-rich foods.
For a long time, nutritionists believed that calcium from plant foods was not well absorbed. Studies from Purdue University reveal this isn't true. Calcium from many plant foods is very well absorbed - in some cases better than calcium from cow's milk.
To meet calcium needs, it is a good idea to make frequent use of foods that are very rich in well-absorbed calcium. For example, make it a point to include leafy green vegetables - such as kale and collard, mustard, and turnip greens - in your meals every day. Be generous as well in your use of calcium-set tofu, calcium fortified soy-milk, calcium-fortified orange juice, blackstrap molasses, and vegetarian baked beans. However, don't overlook the contributions of other foods. Many beans and vegetables provide relatively small amounts of calcium to the diet, but regular use of these foods can contribute several hundred milligrams to the daily intake. Every little bit counts.
However you choose to meet needs, do pay attention to calcium. If you think you aren't coming close to meeting the recommendations of most days, consider a dietary supplement.
One other word of caution. Vegan women have lower levels of estrogen in their blood. While this is protective against breast cancer, it may raise the risk of osteoporosis, because estrogen protects the health of bones. So, it is possible that vegan women may need to take extra steps toward building bone strength.
Calcium myths
There is a great deal of misunderstanding about the relationship of calcium
and protein to bone health in vegans. This is largely due to data that compares the number of hip fractures in different populations.
The number of hip fractures in a population is often used as a measurement to determine the rate of osteoporosis in that population. The assumption is that groups with poor bone health will have more hip fractures. Worldwide, populations that eat predominantly plant-based diets have the lowest rates of hip fracture - despite the fact that they have low intakes of dairy foods and calcium. In fact, where people drink the most cow's milk, hip-fracture rates are highest. Not surprisingly, protein intake is also high in these groups. Looking at these findings, it's easy to assume that too much dietary protein is worse for bone health than too little calcium. In fact, some people have suggested that diets low in calcium are perfectly healthful as long as the diet is low in protein as well. But it isn't that simple.
Hip fracture rates don't always tell the whole story about bone health. In some Asian countries with low hip-fracture rates (and low calcium intakes), bone health is actually poorer. That is, people may not fracture their hips often, but they have poorer bone density and more fractures of other bones. So why don't they break their hips? There are any number of explanations. One of the most critical is that Asians have a particular hip structure that is resistant to breakage. This has nothing to do with diet or bone density; it's purely a genetic phenomenon. Another reason is that many of these populations reside in warmer climates. Without slippery snow and ice to contend with, people are less likely to fall. Finally, physically active lifestyles are the norm in many of these countries, resulting in better balance and strength in old age and therefore fewer falls.
Apparently, there are reasons for the low rates of hip fractures in these groups that have nothing to do with bone health at all. Even where bone health is better and bones are denser, it isn't always reasonable to point to low-protein diets as the cause. Too many other factors clearly affect bone density in different cultures. Physical activity is one of the most important bone protectors. In populations where bone health is better, it is nearly always true that people are more active. They may also consume less protein, but this is likely much less important than excercise. There are genetic influences here as well; for example, people of African descent metabolize calcium differently so that, all other things being equal, they need less calcium to maintain healthy bones.
On the basis of hip-fracture rates, some people have even suggested that cow's milk actually causes poor bone health because it is a high-protein food. Hip fractures are more common where people drink cow's milk, and cow's milk is indeed high in protein. But, as previously stated, hip fractures in fact don't reveal much about bone health - at least in comparison to different cultures. While diets high in protein may indeed increase calcium losses, what really matters is the total ratio of calcium to protein in a particular food or in the overall diet. High-calcium foods promote healthy bones even if those foods are high in protein.
The bottom line? It is a grave mistake to try to draw conclusions about calcium needs of vegans based on hip-fracture data from around the world. They don't tell us anything about calcium requirements. What they do suggest is that bone health is dependent on many factors; genetics, lifestyle, and diet all matter. | 
