Calcium, absorption intake, osteoporosis

Age, calcium intake, hormonal status, exercise and vitamin status have all been implicated in the development of osteoporosis. Estrogen levels represent an important factor in skeletal calcium retention and homeostasis. In therapeutic trials in which post-menopausal women were given daily doses of estrogens, such therapy has been demonstrated to be partially effective in reducing the rate of bone resorption. However, this therapy has the concomitant hazard of endometrial cancer (10). Vitamin D and its hormones have been given considerable attention in the more recent studies. Without adequate dietary and tissue levels of such vitamins, calcium absorption and bone status will be impaired. 

Low lactase activity has been suggested as a factor leading to osteoporosis as a result of either reduced calcium intake or reduced calcium absorption. However, results are conflicting and further studies will be necessary to resolve this question (Paige and Bayless 1981). The relationship between irritable bowel syndrome and lactase deficiency is still unclear, but hypolactasia does not appear to be a major problem in patients with this condition (Paige and Bayless 1981). 

Calcium Adequate calcium intake is required to maintain bone mineral density and reduce the risk of osteoporosis in the elderly. In addition to the reduced absorption of calcium by elderly people that results from age-related changes in vitamin D metabolism, the elderly also show a reduced ability to increase the efficiency of calcium absorption as an adaptive response to low-calcium diets. Also, as noted earlier, the low-acid conditions resulting from atrophic gastritis can reduce calcium absorption. Dietary calcium reacts with hydrochloric acid in the stomach to form soluble calcium chloride, which is absorbed in the small intestine. In the United States, the recommended calcium intake is 1200mg/day for men and women older than age 70. Many elderly people may benefit from calcium supplements. 

In extensive studies of the effect of fluoride In patients with osteoporosis carried out In this Research Unit, a therapeutic dally dose of 45 mg fluoride per day was used as sodium fluoride. The main effect of fluoride on calcium metabolism was a decrease of the urinary calcium, while the fecal calcium did not change and the calcium balance also remained unchanged. Also, the Intestinal absorption of calcium remained unchanged during the high fluoride Intake (Table I), The decrease In urinary calcium, Induced by sodium fluoride, may be due to decreased bone resorption, a very desirable effect for patients with osteoporosis. 

There seems to be little reason to suspect that the elderly have a tendency to be deficient, or even marginally deficient, in zinc (Wood et al., 1995). On the other hand, an emerging concern is that increased calcium intake can interfere with zinc absorption or retention (Sandstead and Smith, 1996). A study of postmenopausal women revealed that supplements of zinc plus calcium seemed to prevent bone loss, while supplements of calcium only permitted bone loss (Strause et al, 1994). Hence, there is some interest in the question of whether persons taking calcium, with the possible effect of preventing osteoporosis, should also take zinc supplements. 

But even in osteoporosis due to calcium deficiency we have no means of judging whether the condition has resulted from a lack of absorption of calcium, or indeed whether this factor has played any role whatsoever in its causation. For as is well known calcium is not only absorbed from the intestinal canal, but is excreted into it. It is evident therefore that the calcium in the feces represents not only calcium which has failed to be absorbed but likewise that which has been absorbed and not utilized. We have no means of separating the two fractions and do not know even approximately the percentage of calcium normally excreted through the intestinal wall. In view of this situation it is clear, especially as the alimentary canal constitutes the main path both of intake and output of calcium, that we are in no position to study the question of absorption of calcium. ... 

Even though osteoporosis may not be preventable by increasing calcium intake, there are reports that calcium supplements have induced calcium retention and relieved symptoms. This may reflect the fact that, although the efficiency of absorption decreases with the amount of calcium in the diet, the total amount of calcium actually retained increases. 

CALCIUM RELATED DISEASES. Diseases may be caused by (1) inadequate intake of calcium or (2) factors inhibiting its absorption or excretion. The clinical manifestations of calcium related diseases are rickets, osteomalacia, osteoporosis, hypercalcemia, tetany, and renal calculi (kidney stones). 

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