Hormones, weight change and menopause.

OBJECTIVE: To determine total body weight change occurring in women at mid-life, specifically with respect to occurrence of menopause and use of estrogen. DESIGN: Retrospective analysis of body weight measurements accumulated in two cohorts of healthy women participating in studies of skeletal metabolism. SUBJECTS: Cohort 1: 191 healthy nuns enrolled in a prospective study of osteoporosis risk, aged 35-45 in 1967; cohort 2: 75 women aged 46 or older and still menstruating, enrolled in 1988 in a study of bone cell dynamics across menopause. Roughly one-third of each group received hormone replacement after menopause. MEASUREMENTS: Body weight and height, age, menstrual status and use of estrogen replacement. Cohort 1: 608 measurements at 5 y intervals spanning a period from 17 y before to 22 y after menopause; cohort 2: 1180 measurements at 6-month intervals spanning a period from 5 y prior to 5 y after menopause. RESULTS: In cohort 1 weight rose as a linear function of age (both chronological and menopausal), both before and after cessation of ovarian function, at a rate of approximately 0.43% y(-1). Neither the menopausal transition nor the use of estrogen had an appreciable effect on this rate of gain. In cohort 2 the rate of gain seemed to diminish slightly at menopause. As with cohort 1, hormone replacement (or its absence) had no appreciable effect on weight. CONCLUSIONS: The long-term, total body weight trajectory at mid-life is not influenced appreciably by either cessation of ovarian function or by hormone replacement.

Calcium intake and body weight.

Five clinical studies of calcium intake, designed with a primary skeletal end point, were reevaluated to explore associations between calcium intake and body weight. All subjects were women, clustered in three main age groups: 3rd, 5th, and 8th decades. Total sample size was 780. Four of the studies were observational; two were cross-sectional, in which body mass index was regressed against entry level calcium intake; and two were longitudinal, in which change in weight over time was regressed against calcium intake. One study was a double-blind, placebo-controlled, randomized trial of calcium supplementation, in which change in weight during the course of study was evaluated as a function of treatment status. Significant negative associations between calcium intake and weight were found for all three age groups, and the odds ratio for being overweight (body mass index, >26) was 2.25 for young women in the lower half of the calcium intakes of their respective study groups (P: < 0.02). Relative to placebo, the calcium-treated subjects in the controlled trial exhibited a significant weight loss across nearly 4 yr of observation. Estimates of the relationship indicate that a 1000-mg calcium intake difference is associated with an 8-kg difference in mean body weight and that calcium intake explains approximately 3% of the variance in body weight.

Association of bone dimensions with a parathyroid hormone gene polymorphism in women.

We have recently shown that bone radiogrammetric dimensions are associated with vitamin D receptor gene polymorphism. Since parathyroid hormone (PTH) plays a central role in maintaining calcium homeostasis and in bone remodeling, we investigated whether bone radiogrammetric dimensions are associated with a PTH gene polymorphism in 91 healthy Caucasian women, who were premenopausal at entry into the study. These women had assessments of bone by radiogrammetry every five years for a median period of 20 years (range 4-27). DNA was extracted from white blood cells. A segment of the PTH gene with a polymorphism at a BstBI restriction site was amplified by polymerase chain reaction. Diameter, cortical thickness and cross-sectional area at standard sites of the metacarpals, radius and femur were measured with radiogrammetry. Higher metacarpal diameter and cross-sectional cortical area, and a slower decrease in radial cortical area with age, were associated with the absence of the BstBI restriction site of the PTH gene. PTH gene polymorphism accounts for about 7-9% of the total variances of bone dimensional variables. These findings suggest that the dimensions of long bones are influenced by allelic variations in the PTH gene or in genes nearby.

Absorption of calcium as the carbonate and citrate salts, with some observations on method.

Calcium supplement use has increased and there is confusion about the relative absorbability of various sources. Absorbability of calcium from the carbonate and citrate salts was compared at 300 mg and 1000 mg calcium loads, ingested as part of a light breakfast meal. Absorption was measured at the high load both by tracer appearance in serum and by the absorptive increment in urinary calcium, and at the low load by the tracer method only. Subjects were 37 healthy adult men and women, studied as outpatients, and each tested on both salts at the same load. Mean tracer absorption (+/- SD) for both salts combined was 36.0% at the 300 mg load and 28.4% at the 1000 mg load. In both experiments the observed mean difference in absorption between salts was very small. By the tracer method the within-subject difference (carbonate less citrate) was +3.3% +/- 1.2% of the ingested dose (mean +/- SEM; P < 0.05) at the high load, and at the low load, 3.6% +/- 2.7% (NS). Combining the two experiments yielded zero difference between sources. By the urinary calcium increment method, the mean difference between salts at the 1000 mg load was 1.8 +/- 4.1 mg (NS). Side-by-side comparisons of the two methods revealed that the tracer method was 3 times more sensitive than the urinary increment method. We conclude that, when taken with food, calcium from the carbonate salt is fully as absorbable as from the citrate, and that the urinary increment method is not sufficiently sensitive to be useful in comparing sources in free-living subjects.

Vitamin D and its major metabolites: serum levels after graded oral dosing in healthy men.

We determined the quantitative relationships between graded oral dosing with vitamin D3, 25(OH)D3, and 1,25(OH)2D3 for short treatment periods and changes in circulating levels of these substances. The subjects were 116 healthy men (mean age, 28 +/- 4 years, with usual milk consumption of < or = 0.47 l/day and mean serum 25(OH)D of 67 +/- 25 nmol/l). They were distributed among nine open-label treatment groups: vitamin D3 (25, 250 or 1250 micrograms/day for 8 weeks), 25(OH)D3 (10, 20 or 50 micrograms/day for 4 weeks) and 1,25(OH)2D3 (0.5, 1.0 or 1.0 microgram/day for 2 weeks). All treatment occurred between January 3 and April 3. We measured fasting serum, calcium, parathyroid hormone, vitamin D3, 25(OH)D and 1,25(OH)2D immediately before and after treatment. In the three groups treated with vitamin D3, mean values for circulating vitamin D3 increased by 13, 137 and 883 nmol/l and serum 25(OH)D increased by 29, 146 and 643 nmol/l for the three dosage groups, respectively. Treatment with 25(OH)D3 increased circulating 25(OH)D by 40, 76 and 206 nmol/l, respectively. Neither compound changed serum 1,25(OH)2D levels. However, treatment with 1,25(OH)2D3 increased circulating 1,25(OH)2D by 10, 46 and 60 pmol/l, respectively. Slopes calculated from these data allow the following estimates of mean treatment effects for typical dosage units in healthy 70-kg adults: an 8-week course of vitamin D3 at 10 micrograms/day (400 IU/day) would raise serum vitamin D by 9 nmol/l and serum 25(OH)D by 11 nmol/l; a 4-week course of 25(OH)D3 at 20 micrograms/day would raise serum 25(OH)D by 94 nmol/l; and a 2-week course of 1,25(OH)2D3 at 0.5 microgram/day would raise serum 1,25(OH)2D by 17 pmol/l.

Calcium absorptive effects of vitamin D and its major metabolites.

The absorptive response to graded doses of vitamin D3, 25(OH)D, and 1,25(OH)2D was measured in healthy adult men after treatment periods of eight, four, and two weeks, respectively. While no relationship was found between baseline absorption and serum vitamin D metabolite levels, all three vitamin D compounds significantly elevated 45Ca absorption from a 300 mg calcium load given as part of a standard test meal. 1,25(OH)2D was active even at the lowest dose (0.5 microgram/day), and the slope was such that doubling of absorption would occur at an oral dose of approximately 3 micrograms/day. 25(OH)D was also active in elevating absorption and did so without raising total 1,25(OH)2D levels. On the basis of the dose response curves for 1,25(OH)2D and 25(OH)D, the two compounds exhibited a molar ratio for physiological potency of approximately 100:1. The absorptive effect of vitamin D3 was seen only at the highest dose level (1250 micrograms, or 50,000 IU/day) and was apparently mediated by conversion to 25(OH)D. Analysis of the pooled 25(OH)D data from both the 25(OH)D- and vitamin D3-treated groups suggests that approximately one eighth of circulating vitamin D-like absorptive activity under untreated conditions in winter may reside in 25(OH)D. This is a substantially larger share than has been predicted from studies of in vitro receptor binding.

Bone dimensional change with age: interactions of genetic, hormonal, and body size variables.

Changes in bony dimensions with age were assessed longitudinally from standardized X-ray films in 170 middle-aged Caucasian women, starting at age 40 years and with a median duration of observation of 21.125 years. Consistent with earlier work, cortical area of the metacarpals and radial shaft declined with age at rates ranging from 0.57 to 0.86%/year. As predicted, estrogen replacement therapy decreased this loss in a dose-dependent manner. Not previously reported is the fact that weight gain over the period of observation reduced upper extremity bone loss. Moreover, this protection was independent of the estrogen effect. In contrast with bone loss in the upper extremity, both femur shaft diameter and femur shaft cortical area increased significantly with age (0.23 and 0.26%/year, respectively). Estrogen replacement therapy inhibited femur shaft expansion but had no effect on femur cortical area. Weight change, however, strongly influenced gain (or loss) of femur cortical area: those in the highest weight change tertile gained 4 times as much cortical area as those in the lowest weight change tertile. VDR genotype also significantly influenced femoral shaft changes: women with the bb genotype had both greater shaft expansion and a greater increase in cortical area. The VDR effects were independent of the effects of weight change and estrogen. Femoral shaft expansion was of sufficient magnitude to suggest that the mechanical properties of the entire femur may change appreciably with age. Finally, contrary to widespread belief, there was significant, if modest, expansion at the femoral neck with age.

Vitamin D receptor gene polymorphism, bone mass, body size, and vitamin D receptor density.

We determined vitamin D receptor (VDR) gene alleles (based on the BsmI restriction site polymorphism), duodenal mucosal receptor density, bone mass at spine and total body, and body size in 32 healthy premenopausal females. While we found no relationship between allele and receptor density in duodenal mucosa, bone mineral content (BMC) at both spine and total body was significantly associated with VDR gene alleles. BMC was highest for the bb allele, lowest for BB, and intermediate for Bb. A similar association was noted between allele and body size variables, particularly weight. When BMC was adjusted for body weight, the association with VDR polymorphism disappeared. The VDR gene polymorphism may be affecting bone mass not through classical nutritional mechanisms (e.g., intestinal calcium absorption), but through an influence on body size.

Caffeine and the calcium economy revisited.

We report an analysis of data from 560 calcium balance studies carried out on 190 women aged 34.8-69.3 years at the time of study. The main purposes were to confirm a previously observed association between caffeine intake and calcium balance, and to attribute the association, if possible, to specific component(s) of balance. We found a caffeine relationship such that for every 6 fl oz (177.5 ml) serving of caffeine-containing coffee, calcium balance was more negative by 0.114 mmol/day (4.6 mg/day) (P < 0.001). The relationship was localized to the input side of the balance equation, and both of its components (i.e. calcium intake and calcium absorption efficiency) were independently and inversely associated with caffeine intake. There was no evidence that the putative caffeine effect is confined to, or is greater among, subjects with low calcium intakes or those who are older or estrogen-deprived. The magnitude of the negative effect of caffeine on calcium balance suggests that it can be offset by increasing calcium intake by about 1 mmol (40 mg) for every 177.5 ml serving of caffeine-containing coffee.

An investigation of sources of variation in calcium absorption efficiency.

To examine putative sources of interindividual variation in calcium absorption efficiency, we studied 41 healthy premenopausal women (mean age, 36.4 yr). About half were randomized to pretreatment with supplemental 25-hydroxyvitamin D (25OHD; 20 micrograms/day [corrected] for approximately 34 days) before testing. We measured dietary factors, humoral regulators, intestinal motility, mucosal histology, mucosal vitamin D receptor levels, and calcium absorption efficiency. In winter tests, but not in summer tests, calcium absorption fraction was significantly higher in the pretreated group (mean, 0.465 vs. 0.387). Serum 25OHD, intestinal transit, and urinary calcium to creatinine ratio were all significantly and positively correlated to calcium absorption efficiency. However, neither the level of 1,25-dihydroxyvitamin D receptors in duodenal mucosa nor circulating 1,25-dihydroxyvitamin D was related to calcium absorption efficiency. These findings, which are consistent with other published human data, suggest that 25OHD plays a more prominent role in the regulation of calcium absorption than is generally believed. In a multiple regression model, serum 25OHD, mouth to cecum transit time, and fasting urinary calcium/creatinine ratio explained 44% of the observed variation in calcium absorption efficiency.

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.

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.

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.

Effects of moderate caffeine intake on the calcium economy of premenopausal women.

We examined directly the effects of a moderate dosage of caffeine (400 mg/d) on the calcium economy in 16 healthy premenopausal women in a double-blind, placebo-controlled crossover design. The subjects took divided doses of caffeine (100 mg/tablet) or identical-appearing placebos with decaffeinated coffee on personalized schedules for treatment periods lasting 19 d each and with 37-d interstudy intervals. We randomized the treatment sequence among subjects and studied them as inpatients under metabolic-balance conditions. We found no significant effects of caffeine on fractional calcium absorption, endogenous fecal calcium, or urine calcium, whether examined day by day or cumulatively. Although the mean balance shift was negative, the change was not significantly different from zero. There was evidence of altered bone remodeling, with slight decreases in bone accretion, bone resorption, and calcium pool turnover.

Time course of calcium absorption in humans: evidence for a colonic component.

We examined the time course of calcium absorption (CaAbs) in 155 studies, using a double isotope technique. The subjects were 118 healthy peri-menopausal women (mean age 53.3 years), studied as inpatients under metabolic balance conditions. We measured the ratio of radiolabeled calcium (oral:IV) in serum and urine for 144 hours after the oral dose, and generated a composite CaAbs curve for all 155 studies using normalized data. Although CaAbs was 80.9% complete at 3 hours, it was still only 95.8% complete at 7 hours; the remaining 4.2% was absorbed in a slower late component, and did not reach completion until about 26 hours. The rapid initial component probably represents mainly small intestinal absorption and the late component, colonic. At the dietary intakes of our subjects, we estimate the size of the late component at about 6.8 mg/day. For fully accurate measurements of CaAbs, it is necessary to allow for this small late component.

Calcium absorbability from milk products, an imitation milk, and calcium carbonate.

Whole milk, chocolate milk, yogurt, imitation milk (prepared from dairy and nondairy products), cheese, and calcium carbonate were labeled with 45Ca and administered as a series of test meals to 10 healthy postmenopausal women. Carrier Ca content of the test meals was held constant at 250 mg and subjects fasted before each meal. The absorbability of Ca from the six sources was compared by measuring fractional absorption by the double isotope method. The mean absorption values for all six sources were tightly clustered between 21 and 26% and none was significantly different from the others using one-way analysis of variance. We conclude that none of the sources was significantly superior or inferior to the others.