Absorbability of the calcium in a high-calcium mineral water

The availability of the calcium contained in a high-calcium mineral water (Sangemini), popular in Italy, was compared in 18 healthy women with the availability of milk calcium ingested at the same calcium load, using 45Ca as the tracer in a randomized cross-over design. At an ingested calcium load of 2.5 mmol, absorption fraction averaged 0.433 for milk and 0.475 for Sangemini water. The mean quotient of the two (Sangemini/milk) was 1.129 (+/- 0.056, SEM, P < 0.05). The calcium of Sangemini water is thus highly bioavailable, and at least as bioavailable as milk calcium.

Relationship between balance and dual tracer isotopic measurements of calcium absorption and excretion

Calcium (Ca) absorption was measured by the balance method and the dual tracer isotopic method in 462 studies of adult women. Results for both fractional absorption and net Ca balance were similar using the 2 methods. Slightly higher values (mean difference, 0.031 +/- 0.092) were found for fractional absorption measured by the balance method than by the isotopic method. No differences in fractional absorption between the methods were seen at a fractional absorption less than 25%. Variability in the data was greater from the balance than the isotopic method. Endogenous fecal Ca excretion was directly related to Ca intake, with an estimated value of 70-80 mg/day for a Ca intake less than 200 mg/day. These findings support the usefulness and accuracy of isotope-based measures of mineral absorption. No evidence is found from these or previous data to suggest that the process of isotopic equilibration falsely increases estimates of absorption or endogenous excretion in tracer studies. Isotopic techniques allow studies of calcium absorption in diverse populations and evaluation of unique aspects of mineral metabolism not accessible through other techniques.

The bone-remodeling transient: implications for the interpretation of clinical studies of bone mass change

A computer simulation of the bone-remodeling transient is described, in which the focus is explicitly on changes in clinically measurable bone mass (or density). Based upon quantitative remodeling data accumulated by histomorphometry and calcium tracer kinetics, the simulation shows that much of the apparent gain in bone produced by several agents currently employed to treat osteoporosis can be explained as a remodeling transient rather than as a fundamental alteration of remodeling balance. Even gains as large as 30% or more can be produced by nothing more than the remodeling transient under certain plausible combinations of basal remodeling rate, remodeling period, and degree of bone loss. The simulation further highlights the importance, in evaluating bone-active agents, of separating the response across the first remodeling period from bone changes that may ensue thereafter.

Determinants of endogenous fecal calcium in healthy women

Endogenous fecal calcium (EFC) excretion was measured in 518 studies in 191 normal perimenopausal women, most studied two to three times over a 15 year period. EFC averaged 102 +/- 25 mg/day. Absorption fraction was simultaneously determined by both double-isotope and balance methods. EFC was found to vary inversely with absorption fraction, and the observed relationship was used to calculate the total amount of calcium (TIC) entering the gut from endogenous sources. TIC averaged 140 +/- 34 mg/day and was found to be correlated with a number of intake and body size variables. Phosphorus intake was the most strongly correlated of all the variables (r = 0.404; P < 0.0001), each increment of 0.1 g phosphorus intake being associated with an increase in TIC of 6 mg. Lean body mass was the best correlated of the body size variables, with TIC rising by 1.6 mg/day for every kg lean mass. There were also small but significant correlations with protein and energy intakes, the latter suggesting that some of the variation of TIC is related to the amount of food consumed. Caffeine, previously reported as elevating TIC, did not exhibit a significant relationship in this study.

Osteoporosis-2044

It is likely that by 2044 biomedical and public health forces will be able to control bony fragility to a substantially greater degree than we have succeeded in doing today, but that demographic and lifestyle forces already at work will offset those gains, perhaps substantially. On the other hand, economic and social forces outside of our control will decrease the prevalence of skeletal fragility--harshly, I fear--either by strengthening old bones the hard way, or by decreasing the numbers of the elderly, or both. The final outcome will be the algebraic sum of the effects of these countervailing forces, which is impossible to estimate with any assurance. My guess is that osteoporosis will be less of a problem in 2044, though, unfortunately, for the wrong reasons.

The role of calcium intake in preventing bone fragility, hypertension, and certain cancers

This paper examines the evidence that connects calcium intake and vitamin D status to bone fragility, hypertension, colon cancer, and breast cancer. Human calcium physiology, with an intestinal absorptive barrier and inefficient conservation, reflects the abundance of calcium in the primordial human food supply. The calcium intake of stone-age adults is estimated at 50 to 75 mmol/d, three to five times the median calcium intake of present-day U.S. adults. Long-term calcium restriction and/or insufficient vitamin D may promote the development of bone fragility, high blood pressure, colon cancer, and breast cancer in susceptible individuals. Conversely, improvement in calcium intake and/or in vitamin D status may help to prevent these serious health problems. At least 12 intervention studies have established the skeletal benefit of increased calcium intake among women in the late postmenopause. Other reports suggest that adequate calcium may protect against salt-sensitive and pregnancy-associated hypertension. High intakes of both dietary calcium and vitamin D are associated with reduced development of precancerous changes in colonic mucosa. Preliminary findings also suggest that vitamin D has a protective effect against breast cancer.

Velocity of ultrasound and its association with fracture history in a rural population

The authors set out to determine the distribution of bone quality, as measured by ultrasound, in a rural Nebraska population of women and men. Noninstitutionalized residents of Saunders County, Nebraska, who were age 50 years or older as of January 1, 1992, were enumerated. From this sampling frame, a randomized proportionate stratified sample was selected. The response rate to this random sampling was 58%. Bone quality was measured using the apparent velocity of ultrasound (AVU) through the patella. In addition to demographic information, participants were asked to describe all fractures that had occurred since age 40 years. Fractures were classified as resulting from low or high trauma. Like bone mass, previously studied extensively, AVU was lower among successively older strata for both sexes. AVU discriminated between those with and those without low-trauma or any fractures for both sexes, whether unadjusted or adjusted for nonresponse. AVU is a faster, cheaper, and less time-consuming procedure than bone mass. The measuring device is portable and is well suited for population-based studies. It remains to be determined, by prospective methods, whether AVU is a predictor of low-trauma or osteoporotic fracture in this population.

ADSA Foundation Lecture. Low calcium intake: the culprit in many chronic diseases

Calcium is the fifth most abundant element in the earth's crust and is necessary for both plant and animal life today. Moreover, the natural diets of all mammals are rich in calcium. The diet of Stone Age human adults is estimated to have contained from 50 to 75 mmol of calcium (2000 to 3000 mg)/d, three to five times the median calcium intake of present-day US adults. Human physiology has adapted to this environmental abundance with an intestinal absorptive barrier and inefficient renal conservation of calcium. Although mammalian physiology contains mechanisms by which organisms can adjust to temporary environmental shortages, chronic calcium retention has a number of health consequences, most notably bone fragility, high blood pressure, and colon cancer. Evidence indicates that improvement in calcium intake (or in vitamin D status) prevents some portion of each of these multifactorial problems. At least 14 intervention studies have established the skeletal benefit of increased calcium intake during growth and among women in the late postmenopause. Other evidence suggests that adequate calcium may protect against salt-sensitive and pregnancy-associated hypertension and that high intakes of both dietary calcium and vitamin D reduce development of precancerous changes in colonic mucosa.

Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. Inference from a cross-sectional model

To determine the timing of peak bone mass and density, we conducted a cross-sectional study of bone mass measurements in 265 premenopausal Caucasian females, aged 8-50 yr. Bone mass and bone mineral density were measured using dual X-ray absorptiometry and single-photon absorptiometry at the spine (anteroposterior, lateral), proximal femur, radius shaft, distal forearm, and the whole body. Bone mass parameters were analyzed using a quadratic regression model and segmented regression models with quadratic-quadratic or quadratic-linear form. The results show that most of the bone mass at multiple skeletal locations will be accumulated by late adolescence. This is particularly notable for bone mineral density of the proximal femur and the vertebral body. Bone mass of the other regions of interest is either no different in women between the age of 18 yr and the menopause or it is maximal in 50-yr-old women, indicating slow but permanent bone accumulation continuing at some sites up to the time of menopause. This gain in bone mass in premenopausal adult women is probably the result of continuous periosteal expansion with age. Since rapid skeletal mineral acquisition at all sites occurs relatively early in life, the exogenous factors which might optimize peak bone mass need to be more precisely identified and characterized.

Bone mass, nutrition, and other lifestyle factors

Since the proceedings of the last Consensus Conference on Osteoporosis were published as a supplement to The American Journal of Medicine in November 1991, there has been a plethora of well-documented studies reported in the literature. This article will address some of the issues concerning the relation between bone mass and nutrition raised in those studies.

Revisable criteria for vertebral deformity

In order to study vertebral fractures in various study populations, we earlier prepared a database of vertebral dimensions derived from spinal radiographs of 191 normal women seen regularly over 25 years. In this report we have expanded the range of measurements to include vertebral levels T3 to L5. We report means and standard deviations on anterior and posterior heights, on wedge shape and on heights relative to adjacent vertebrae. When one or both of the latter two quantities are 'far' below the mean, a vertebra is called deformed. We also describe a more flexible way of expressing damage using the number of deformed vertebrae, the degree of deformity of individual vertebrae, or the total damage to the entire spine. In assessing damage we use criteria for deformity adjusted to the limits detected by an experienced diagnostician, replacing an earlier approach based on 95% probability limits of normal variation. The normal women from whom these variations are ascertained are a low-prevalence group with respect to vertebral deformity, with prevalence of 2.8%. When the criteria developed from these women were applied to a moderate-prevalence group (37%) the model had a sensitivity of 97%, a specificity of 89% and an accuracy of 92% as regards the identification of subjects with damaged vertebrae. When used epidemiologically for a moderate-prevalence group the model has a known overestimation of 15%. the model is compared with other schemes for identifying vertebral deformities.

Effects of calcium restriction on metabolic characteristics of premenopausal women

We studied 28 healthy premenopausal women before and after manipulating Ca intake, and then in response to a hypercalcemic challenge. Women with low Ca intakes at entry (< 17.5 mmol/day) were restricted to about 5 mmol/day (low-Ca), and those with higher self-selected intakes were supplemented to about 70 mmol/d (high-Ca). After 8 weeks on these regimens, more bone resorption was occurring among the low-Ca women, as evidenced by their higher values for immunoreactive PTH and urine hydroxyproline. There was a 7-fold range in 24-h urine Ca among the low-Ca women, with upper values equivalent to about 80% of intake. In response to induced hypercalcemia (0.5 mmol Ca/kg lean body mass, infused over 4 h), the low-Ca group had greater increases in serum Ca (1.31 vs. 1.05 mmol/L, P < 0.05) and reached a marginally higher peak (3.64 vs. 3.50 mmol/L, P < 0.1). Despite these greater calcemic responses, the low-Ca women excreted a smaller fraction of the infused Ca (44.3 vs. 62.2%, P < 0.02). Furthermore, preinfusion urine Ca was directly correlated with excretion of infused Ca in the low-Ca women, but not in the high-Ca women. Preinfusion differences between groups in immunoreactive PTH and urine hydroxyproline tended to reappear within 2 days. Our findings show that there are detectable differences in the Ca regulatory system between subjects at practical extremes of Ca intake, and that these differences persist through exposure to a temporary Ca surfeit. Ca-restricted women have higher levels of PTH and of bone remodeling activity. There is considerable variation in the apparent capacity to conserve Ca among women with low intakes. None of our subjects had high-P diets. Thus, our findings show that Ca restriction can evoke a persistent PTH response in the absence of a high P intake.

Bone gain in young adult women

OBJECTIVE

To test whether bone mass increases in healthy nonpregnant white women during early adult life after cessation of linear growth; and to test whether various self-chosen levels of physical activity and nutrient intake or use of oral contraceptives influences this increase in bone mass.

DESIGN

Longitudinal prospective study of up to 5 years of 156 healthy college-aged women full-time students attending professional schools in universities in the Omaha, Neb, area.

SETTING

University medical center.

PARTICIPANTS

A convenience sample of healthy women students from Omaha-area professional schools. Any candidate with an illness, condition, or medication (except oral contraceptives) thought to affect general health or bone mass was excluded.

INTERVENTIONS

None.

OUTCOME MEASURES

Clinical and family histories of disease, particularly osteoporosis; oral contraceptive use; bone mineral densities of the spine, forearm, and total body by dual- and single-photon absorptiometry; estimates of nutrient intake by repeated 7-day diet diaries; and measures of physical activity using a physical activity monitor.

RESULTS

The median gain in bone mass for the third decade of life, expressed as a percentage per decade, was 4.8% for the forearm, 5.9% for lumbar bone mineral content, 6.8% for lumbar bone mineral density, and 12.5% for total body bone mass (P < .0001 in all cases). By both bivariate and multiple regression analysis the rate of gain in bone density of the spine was negatively correlated with age and positively correlated with calcium/protein intake ratio and physical activity (multiple r = .31; P = .004). Bivariate analysis showed that use of oral contraceptives was associated with greater gain in total body bone mass (r = .31, P = .01). The estimated age when mineral acquisition ceased ranged from 28.3 years to 29.5 years at the several study sites.

CONCLUSIONS

Gain in bone mass occurs in healthy young women during the third decade of life. Physical activity and dietary calcium intake both exert a positive effect on this bone gain. Use of oral contraceptives exerts a further independent positive effect. Changes in life-style among college-aged women, involving relatively modest increases in physical activity and calcium intake, may significantly reduce the risk of osteoporosis late in life.

Fracture risk as determined by prospective and retrospective study designs

Both retrospectively and prospectively designed studies consistently show low bone mass and/or bone mineral content (BMC) to be risk factor for low-trauma fractures in postmenopausal women. Along with the reports of such studies there has been concern expressed that BMC measurements overlap between fracture groups, i.e., some women with high BMC develop fractures and some women with low BMC do not. In these commonly used epidemiologic study designs, BMC does not discriminate between those who have and have not experienced the untoward event at some level of the exposure factor. The ability to discriminate is more properly determined by the sensitivity and specificity of the measured value. To contrast the concepts of risk and sensitivity, a nested case-control study was conducted within a 24-year cohort study of women at risk for osteoporosis. We found that for each 1.0 decrement of BMC z-scores, the adjusted relative risk for the prospective study design was 1.67, while the odds ratio obtained from the most recent BMC z-score measurements was 1.87. A receiver operating characteristic (ROC) curve, calculated from the nested case-control study data, showed that BMC z-scores, measured after low-trauma fracture, have both low sensitivity and low specificity to detect existing fracture status.