Effects of different calcium sources on iron absorption in postmenopausal women

Article Abstract:

Calcium supplements are increasingly used to prevent and treat osteoporosis, a disease in which bone mass is diminished, predisposing the individual to fractures. But consuming supplements of a single nutrient frequently disturbs the metabolism of other nutrients in the body, and this appears to be the case with calcium and iron. Some studies have demonstrated that calcium inhibits the absorption of iron. Nineteen healthy postmenopausal women aged 52 to 72 consumed 500 milligrams of calcium from different sources at the same meal with a specific amount of iron. The iron was in the form of a radioactive isotope that allowed for measurement of how much was absorbed. The three different sources of calcium were milk, orange juice plus calcium citrate-malate (calcium carbonate, citric acid and malic acid) and calcium citrate-malate (CCM) tablets. Inert placebos were also given instead of a calcium supplement. The retention of iron was highest with the placebo (8.3 percent) and lowest with calcium from milk (3.4 percent). Iron retention was 7.4 percent in the presence of CCM with orange juice and 6.0 percent in the presence of CCM tablets alone. Compared with placebo, the decrease in iron absorption was greater with milk than with CCM because CCM contains citric acid, which enhances iron absorption. Iron retention with CCM plus orange juice did not differ significantly from placebo, probably because of the citric acid in CCM and the ascorbic acid (vitamin C) in orange juice, both of which enhance iron absorption. Thus use of calcium supplements together with a vitamin C source appeared least detrimental to iron absorption. These nutrient interactions are complex and more research is needed to determine whether calcium supplements may predispose certain individuals to iron deficiency. One way to minimize this risk is to consume calcium supplements at a different meal from meals with iron-rich foods such as meats, or between meals. (Consumer Summary produced by Reliance Medical Information, Inc.)

Research, Risk factors, Nutrient interactions, Calcium carbonate, Iron deficiency anemia, High-calcium diet, High calcium diet

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Calcium absorption in elderly subjects on high- and low-fiber diets: effect of gastric acidity

Article Abstract:

Previous studies have shown that the ability to absorb dietary calcium decreases as people grow older. This places the elderly at a greater risk for calcium deficiency and loss of bone mass (osteoporosis). The elderly are encouraged to eat high-fiber diets, but it has been demonstrated that dietary fiber can reduce the absorption of calcium. When fiber is present the calcium will bind to the fiber instead of being absorbed. When the gastric juice in the stomach becomes less acidic, as it commonly does in elderly people, more calcium will bind to the fiber. This suggests that high-fiber diets in elderly people with lower than normal amounts of acid in their stomach (achlorhydria) may greatly reduce the absorption of dietary calcium. To determine the effects of acid and dietary fiber on calcium absorption, a low-fiber meal, a high-fiber meal, and a high-fiber meal with hydrochloric acid added, were given to eight elderly subjects with achlorhydria and nine normal elderly subjects. When the low-fiber meal was consumed, 26 percent of the calcium from the meal was absorbed into the body. When the high-fiber meal was consumed, 19 percent of the calcium from the meal was absorbed into the body. The high-fiber meal plus acid resulted in a 18.9 percent absorption rate. The results were the same for the elderly subjects with achlorhydria and the normal subjects. These findings indicate that calcium absorption is reduced with high-fiber diets, and that the acidity of the stomach is not an important factor. (Consumer Summary produced by Reliance Medical Information, Inc.)

Aged, Elderly, Case studies, Calcium metabolism disorders, Achlorhydria

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Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women

Article Abstract:

Seasonal changes in the density and mineral content of bone have been described, with relatively more thinning of the bones of postmenopausal women occurring in the winter. One possible explanation of this would be vitamin D deficiency during the winter, as vitamin D requires sunlight on the skin to activate it. Levels of parathyroid hormone have also been found to have seasonal variation, being highest in the winter months. Parathyroid hormone encourages bone resorption, or leaching of the mineral content of the bones back into the circulation, which can result in thinning. Approximately 250 postmenopausal women were randomly divided into two groups. Both groups received calcium supplements, previously shown to be of benefit in promoting bone strength, and one group was assigned to receive Vitamin D supplements, while the other was given a placebo. In both groups, bone mass increased in the warmer months, and decreased somewhat in the colder months. However, the rate of bone loss in the vitamin D group was less than that of the placebo group, resulting in a net gain for the vitamin D group. The parathyroid hormone increases expected in the winter months did not occur in the vitamin D-treated group. Increasing vitamin D intake to twice the minimum daily recommended allowance, in conjunction with calcium supplements, was found to slow wintertime bone loss, and improve overall bone density in postmenopausal women. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Evaluation, Drug therapy, Parathyroid hormone, Parathyroid hormones, Menopause, Osteoporosis, Dietary supplements, Vitamin D, Seasonal variations (Diseases)

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