Bone is composed on a number of macrominerals, the most well known of which is calcium. Calcium is an essential divalent cation required by humans for a number of physiological roles, one of which to to provision for the formation of bone. Calcium deficiency causes bone diseases and the link between calcium in the diet and bone health is well established. Osteoporosis is a disease whereby the mineral content of the bone changes, and this facilitates a more porous bone, especially in postmenopausal women. This increased porosity significantly reduces the strength of the bone, and can increase the risk of fractures. Osteoporosis is not fully understood, however, there is good evidence that calcium loss plays a large role in the bone mineral changes that are associated with its aetiology. The loss of calcium has lead researchers to hypothesise that a low intake of calcium may be the cause of osteoporosis. However, supplemental calcium to postmenopausal women with osteoporosis, is not always effective at reversing the condition.
However, calcium does appear to have some beneficial effects with respect to osteoporosis, although they are often small and inconsistent between studies. This may suggest that a low calcium intake is one factor amongst others that is responsible for bone loss with age. Recently the focus of nutritional research has changed because of a paradigm shift in understanding osteoporosis. It is now understood that a chronically low pH, at the lower end of the normal range of pH (normal range 7.35 to 7.45) may cause a loss of calcium from bone. This situation arises because the minerals in bone (such as calcium and magnesium) can be used to form mineral salts with anions in the blood that contribute to low pH, thus acting as buffers against excessive acidity. In this way the minerals in bone are resorbed and enter the blood, where they are then excreted from the body. High protein diets increase acid load in the body and also cause the loss of calcium because the sulphur from protein is converted to sulphuric acid.
However supplemental calcium may effectively treat osteoporosis not because the calcium replaces losses from bone, but because the calcium acts in the blood to counter the chronic low pH that may be the cause of osteoporosis. In this respect, other cationic minerals (potassium and magnesium for example) may also be effective. For example, comparisons between calcium carbonate, calcium citrate and potassium citrate on bone resorption have been performed in young women1. The women consumed a standard diet containing 300 mg calcium along with 1000 mg of calcium from calcium citrate or calcium carbonate, or 2250 mg of potassium citrate. The calcium supplements were effective at reducing the parathyroid hormone (PTH) levels of blood (PHT becomes elevated in calcium deficiency), but only the carbonate form of calcium significantly reduced the resorption of bone. However, the potassium citrate was effective at reducing bone resorption and increasing calcium retention.
Dr Robert Barrington’s Comments: These results support the contention that cationic minerals, including calcium, may be beneficial to bone health because they inhibit bone resorption. However, the mechanism by which this occurs in more controversial. The observation that potassium citrate is effective at inhibiting bone resorption and increasing calcium retention suggests that the mechanism may relate to modifying the pH of the blood rather that directly replacement of the mineral content of the bone. It is also interesting that calcium carbonate was able to significantly lower bone resorption levels, whereas calcium citrate was not. It is often claimed that citrate and other organic forms of calcium are more absorbable than inorganic forms of the mineral (such as calcium carbonate). However, in this study the inorganic carbonate form of calcium was effective at reducing bone resorption, while the organic citrate form was not.