David Cleghorn

Calcium requirement and calcium therapy

The mean calcium requirement of normal adults has been estimated from 212 calcium balances on 84 normal subjects and found to be 578 mg. The calcium allowance required to ensure that 95% of normal adults are in calcium balance is about 900 mg. Calcium requirement is relatively higher than that of phosphorus or magnesium because plasma calcium--and therefore urine calcium--is maintained at the expense of the skeleton in the presence of calcium deficiency, whereas plasma phosphate and magnesium--and therefore urine phosphate and magnesium--fall on phosphorus and magnesium deficient diets. Calcium requirement appears to rise at the menopause, and postmenopausal bone loss can be reduced by calcium supplements. In postmenopausal osteoporosis, the severe negative calcium balance can be corrected by giving calcium or calcium and vitamin D, but vitamin D alone is not beneficial. Similarly, bone loss, height loss and further vertebral compression can be reduced by calcium or calcium and vitamin D but not by vitamin D alone.

Fracture rates as a function of forearm mineral density in normal postmenopausal women: Retrospective and prospective data

SummaryFracture histories were obtained from 492 normal postmenopausal women in 1983 and again in 1988, and related to forearm mineral content and density determined in 1983. All peripheral fractures, except those attributable to road traffic accidents, were included. There was only one hip fracture in the series. The total number of postmenopausal fractures was 183 in 149 subjects. In both the retrospective and prospective studies, fracture rates were inversely related to bone status and more significantly to bone density than to bone mass. In the pooled data, the fracture rate was three times as high in women with bone densities more than 4 standard deviations below the young normal mean as in those with bone densities above the mean. On logistic regression, the adjusted relative risk of fracture (odds ratio) in subjects more than 4 standard deviations below the young mean compared with those above the mean was 5.5 (2.7–11.4).

The 5-year reproducibility of calcium-related biochemical variables in postmenopausal women

A total of 19 measured and derived bone-related biochemical variables were determined in 307 postmenopausal volunteers on two occasions, 5 years apart. The plasma variables with the highest coefficients of determination (r2) were plasma globulins, alkaline phosphatase, creatinine and calculated ionized and ultrafiltrable calcium. In the urine, the highest r2 values were in respect of fasting urine calcium excretion corrected for urine sodium, hydroxyproline excretion, and the maximal renal tubular reabsorption of calcium and phosphate (TmCa/GFR and TmP/GFR). The components of variance of TmCa/GFR and TmP/GFR show marked individuality but their methods determination meet the criterion for acceptable analytical goals. We conclude that most of the measured and derived bone-related biochemical variables in fasting plasma and urine are sufficiently reproducible in postmenopausal women to be useful for ranking individuals for a period up to 5 years.

91152158 Effect of salt restriction on urine hydroxyproline excretion in postmenopausal women

Fasting calcium and hydroxyproline excretion are related to fasting sodium excretion in postmenopausal women. We postulate that calcium excretion is sodium dependent and that hydroxyproline excretion is calcium dependent. Therefore, we sought to lower urinary hydroxyproline, which is a marker of bone resorption, by lowering urinary sodium. Fasting urine samples were obtained from 59 postmenopausal women before and after 2 to 7 days of dietary salt restriction. The urinary sodium-to-creatinine ratio fell from 16 to 7; calcium to creatinine, 0.30 to 0.26; and hydroxyproline to creatinine, 18.2 to 16.8. In the 28 subjects with starting sodium-to-creatinine ratios greater than 15, the hydroxyproline-to-creatinine ratio fell from 19.6 to 16.3. Salt restriction may be one way of reducing bone resorption in postmenopausal women, particularly in those whose sodium intake is high.