A good deal of marketing spin about bone health has been devoted to 'getting enough calcium', through food and preferably supplements. Interestingly, I heard an exercise specialist talk about doing a dissection on an 85-year-old woman. "There were calcium deposits everywhere," she said, "in the muscles, in the joints, in the shoulders-everywhere." Perhaps, it would seem to me, too much calcium has its drawbacks, too.
There is a fallacy in focusing on calcium alone to prevent fractures. Bones are composed of a latticed protein grounding or collagen matrix, which comprises about 35 per cent of the bone and which gives it its flexibility. This matrix is laid down first, and then trapsthe mineral salt calcium phosphate, also known as 'hydroxyapatite', which occupies about 65 per cent of the bone mass and gives the bone its strength.
In addition to the calcium salts, the bones are also the depositories of other minerals needed by the body, including magnesium, sodium, potassium and others. The main component, then, to prevent fractures, is the bone's flexibility, given to it by the collagen matrix, not calcium.
Even though strong and hard, bones are not the equivalent of stones or rocks. Instead, like the rest of the tissues in the body, they are constantly moving and changing. They are continuously being built up, in a process called 'deposition' or 'formation', and just as continuously are being broken down, in a process called 'resorption'.
During childhood and adolescence, this process is called 'modeling', in which old bone is removed and new bone formed at another site of the same bone; some-times, this takes place simultaneously, to allow the bones to grow and shift about in the body.
In adulthood, once the skeleton is set at its adult size, the same process is called 'remodeling', and is more sequential, in that specialized cells called 'osteoclasts' break down and resorb old bone, and other cells called 'osteoblasts' build up new bone in that same site.
In adults, about 5 to 10 per cent of bone is replaced yearly in this fashion, so that most of our adult skeleton is replaced around every 10 years. After the menopause, bone loss in women may accelerate to 2 to 5 per cent per year, depending on a woman's nutritional status, exercise levels, pharmacological drug intake and overall health.
For some time, it was thought that protein weakened bone. However, the formation of collagen is dependent on sufficient supplies of protein in the diet, as well as on vitamin C, which stimulates the enzymes that form collagen and connective tissues. A deficiency of either one of these bone components could weaken the bony matrix, interfering with its ability to hold on to the calcium salts.
In fact, both too much and too little protein can cause trouble with the bones. Some studies show that vegetarians have higher bone density than omnivores, or people who eat everything (but presumably much more animal protein, and perhaps also fewer plant foods). In one study, the mean bone density of the 70- to 79-year-old vegetarians was greater than those of the 50- to 59-year-old omnivores (Am J Clin Nutr, 1988; 48: 837-41). Therefore, it was thought that vegetarians have a lesser risk of osteoporosis than those who eat everything.
Too many sweets
However, another way to interpret these findings is to note the rest of the dietary context: it could mean that the 'omnivores' eat too many sweets, and not enough greens and other plant foods. The relationship between protein and calcium may be crucial: a 1997 Norwegian study found that there was an elevated risk of fracture in women with a high intake of protein and a concomitant low calcium intake.
However, more recent studies show a different picture. The Framingham Osteoporosis Study, from the Harvard Medical School Division on Aging, established in this study of people aged 69 to 91 that those with the lowest protein intake had the most bone loss, and that lower animal-protein intake was also significantly related to bone loss in both the hip and the spine (J Bone Miner Res, 2000; 15: 2504-12). Another study, led by B. Dawson-Hughes from the Bone Metabolism Laboratory at Tufts University, found that a doubling of protein intake from meats, together with a reduction in carbohydrate intake, not only did not increase calcium loss through the urine, but was associated with higher bone growth factors in the blood (J Clin Endocrinol Metab, 2004; 89: 1169-73).
Interestingly, soy proved to be no better than meat in another study, where it was found that the substitution of 25 g of high isoflavone soy protein for meat, in the presence of typical calcium intakes, neither improved nor impaired calcium retention or indicators of bone and cardiovascular health in postmenopausal women (J Clin Endocrinol Metab, 2005;
90: 181-9). It is time to put to rest the outdated notion that meat makes the bones weaker.
People who eat carelessly, focusing on packaged and processed foods and refined carbohydrates, and ignoring vegetables and protein, may be risking weak bones as a result of collagen-matrix insufficiency. Calcium supplements in these cases may be counterproductive: an excess of calcium and a lack of collagen matrix could make the bones hard but brittle, and so more easily breakable.
Annemarie Colbin, PhD
Dr Colbin is an award-winning leader and author in the field of natural health. Visit her website at www.foodandhealing.com .