Vegan for Life by Jack Norris, Virginia Messina Read Free Book Online Page B

calcium storage, providing a steady supply of calcium to the blood where it is needed for muscle relaxation, nerve cell transmission, and a host of other functions. Some of this calcium is regularly lost in the urine and must be replaced by dietary sources. As a result, bones are in motion—breaking down to release calcium to the blood and then taking up new calcium and rebuilding. Getting enough calcium is important for bone health, but reducing the amount that is lost through the urine could be important too.
    Bones grow through the first three decades of life, becoming longer, heavier, and denser. By their late twenties or early thirties, most people have achieved peak bone mass , and their skeleton is as heavy and dense as it is going to get. There is some evidence that peak bone mass determines bone health and risk for osteoporosis in later years.
    Beginning at age forty-five or so, there is a shift in metabolism and bone mass begins to decline. Efforts to slow calcium losses from the body and provide enough calcium to keep bones strong are important for preventing osteoporosis, especially for women, who can begin to lose bone rapidly after menopause.
    Good bone health depends on a complex interplay of factors that affect both absorption of calcium and calcium losses from the body. Diet, lifestyle, and genetics all play a part in calcium balance. Figuring out how these factors interact and affect calcium needs has been an ongoing subject of debate among researchers, and some of the issues may be especially important for vegans.
The Relationship of Calcium Intake to Bone Health
    Calcium is different from other nutrients in that it isn’t associated with an acute deficiency disease. With most nutrients, if your intake is too low, you’ll get sick. That’s not true for calcium because levels in
the blood are very tightly controlled. Even a small change in those levels can be life-threatening, so the body utilizes stored calcium in the bone plus the filtering system of the kidneys to keep calcium concentrations within strict boundaries. You can’t ascertain calcium status by measuring blood levels of this mineral because those levels are always the same. But while a low calcium diet doesn’t cause an acute nutritional deficiency, a chronically low intake can raise the risk for osteoporosis later in life.
    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