Correlates of intestinal calcium absorption in women 10 years past the menopause

Associations between low- and high-fat dairy intake and recurrence risk in people with stage I-III colorectal cancer differ by sex and primary tumour location

We previously demonstrated that intake of low-fat dairy, but not high-fat dairy, was associated with a decreased colorectal cancer (CRC) recurrence risk. These risks, however, may differ by sex, primary tumour location, and disease stage. Combining data from two similar prospective cohort studies of people with stage I-III CRC enabled these subgroup analyses. Participants completed a food frequency questionnaire at diagnosis (n = 2283). We examined associations between low- and high-fat dairy intake and recurrence risk using multivariable Cox proportional hazard models, stratified by sex, and primary tumour location (colon and rectum), and disease stage (I/II and III). Upper quartiles were compared to lower quartiles of intake, and recurrence was defined as a locoregional recurrence and/or metastasis. During a median follow-up of 5.0 years, 331 recurrences were detected. A higher intake of low-fat dairy was associated with a reduced risk of recurrence (hazard ratio [HR]: 0.60, 95% confidence interval [CI]: 0.43-0.83), which seemed more pronounced in men (HR: 0.51, 95% CI: 0.34-0.77) than in women (HR: 0.84, 95% CI: 0.47-1.49). A higher intake of high-fat dairy was associated with an increased risk of recurrence in participants with colon cancer (HR: 1.60, 95% CI: 1.03-2.50), but not rectal cancer (HR: 0.88, 95% CI: 0.54-1.45). No differences in associations were observed between strata of disease stage. Concluding, our findings imply that dietary advice regarding low-fat dairy intake may be especially important for men with CRC, and that dietary advice regarding high-fat dairy intake may be specifically important in people with colon cancer.

Clinical and biomarker modifiers of vitamin D treatment response: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Different 25-hydroxyvitamin D [25(OH)D] thresholds for treatment with vitamin D supplementation have been suggested and are derived almost exclusively from observational studies. Whether other characteristics, including race/ethnicity, BMI, and estimated glomerular filtration rate (eGFR), should also influence the threshold for treatment is unknown.

OBJECTIVES

The aim was to identify clinical and biomarker characteristics that modify the response to vitamin D supplementation.

METHODS

A total of 666 older adults in the Multi-Ethnic Study of Atherosclerosis (MESA) were randomly assigned to 16 wk of oral vitamin D3 (2000 IU/d; n = 499) or placebo (n = 167). Primary outcomes were changes in serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations from baseline to 16 wk.

RESULTS

Among 666 participants randomly assigned (mean age: 72 y; 53% female; 66% racial/ethnic minority), 611 (92%) completed the study. The mean (SD) change in PTH was -3 (16) pg/mL with vitamin D3 compared with 2 (18) pg/mL with placebo (estimated mean difference: -5; 95% CI: -8, -2 pg/mL). Within the vitamin D3 group, lower baseline 25-hydroxyvitamin D [25(OH)D] was associated with a larger decline in PTH in a nonlinear fashion. With baseline 25(OH)D ≥30 ng/mL as the reference, 25(OH)D <20 ng/mL was associated with a larger decline in PTH with vitamin D3 supplementation (-10; 95% CI: -15, -6 pg/mL), whereas 25(OH)D of 20-30 ng/mL was not (-2; 95% CI: -6, 1 pg/mL). A segmented threshold model identified a baseline 25(OH)D concentration of 21 (95% CI: 13, 31) ng/mL as an inflection point for difference in change in PTH. Race/ethnicity, BMI, and eGFR did not modify vitamin D treatment response. There was no significant change in 1,25(OH)2D in either treatment group.

CONCLUSIONS

Of characteristics most commonly associated with vitamin D metabolism, only baseline 25(OH)D <20 ng/mL modified the PTH response to vitamin D supplementation, providing support from a clinical trial to use this threshold to define insufficiency. This trial was registered at clinicaltrials.gov as NCT02925195.

Influence of estrogen therapy on calcium, phosphorus, and other regulatory hormones in postmenopausal women: the MESA study

BACKGROUND

Estrogen therapy (ET) is associated with lower serum calcium and phosphorus concentrations and is known to increase bone mineral density (BMD). Other biomarkers of mineral metabolism may help understand the biological basis of these actions.

METHODS

We studied 2767 postmenopausal women in the Multi-Ethnic Study of Atherosclerosis, 862 (31%) of whom were using ET. We measured serum concentrations of calcium, phosphorus, 25-hydroxyvitamin D, 24,25-dihydoxyvitamin D, and fibroblast growth factor-23 and urinary fractional excretion of calcium (FEca) and phosphorus (FEphos). We examined the associations of ET with each biomarker. In addition, we tested whether the adjustment for biomarkers attenuated the association of ET with lumbar BMD measured by abdominal computed tomography in a subset of 810 women.

RESULTS

In adjusted models, women who used ET were younger in age [62 (SD 8) vs 66 (9) y, P < .001], had lower mean serum calcium [-13 mg/dL (95% confidence interval [CI] -0.17, -0.10), P < .001] and lower FEca [-0.15% (95% CI -0.21, -0.09), P < .001]. Mean serum phosphorus was lower [-0.19 mg/dL (95% CI -0.23, -0.15), P < .001] and FEphos [0.56% (95% CI 0.16, 0.96), P = .007] was higher in women on ET. Mean 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D were higher [1.52 ng/dL (95% CI 0.57, 2.47), P = .002, and 0.26 ng/mL (95% CI 0.03, 0.48), P = .03, respectively] in women who used ET. Mean PTH and fibroblast growth factor-23 did not differ significantly by the use of ET. ET use was strongly associated with higher lumbar BMD [12.75 mg/cm³ (95% CI 7.77-17.73), P < .001]; however, mineral metabolism measures did not meaningfully alter this association.

CONCLUSIONS

In a multiethnic cohort of postmenopausal women, ET use was associated with lower serum calcium, lower FEca, lower serum phosphorus, and higher FEphos, suggesting these associations are attributable to increased calcium intake into bone and increased urinary phosphorus excretion. ET use was also associated with greater concentrations of vitamin D metabolites. ET-associated differences in these mineral metabolism measures did not meaningfully attenuate the strong association between ET use and lumbar BMD.

Impact of dietary intake, education, and physical activity on bone mineral density among North Indian women

The aim of the study was to determine the relationship of dietary nutrients and bone mineral density (BMD) in North Indian women. This cross-sectional study was conducted from April 2006 to March 2008. Subjects included 255 healthy women, aged 20-69 years, who were relatives of patients being admitted in the hospital. Various demographic characteristics including socioeconomic status and serum parameters in relationship to BMD were evaluated. In addition, the daily dietary intake of energy, protein, fat, and calcium and the amount of physical activity were assessed. BMD at the lumbar spine, femoral neck, and Ward's triangle was measured by dual-energy X-ray absorptiometry (DXA). Body mass index (BMI), physical activity, and educational level were positively correlated with BMD. The daily intakes of energy (1563.4 +/- 267.2 kcal) and protein (48.7 +/- 8.7 g) were below the recommended dietary allowance. Daily dietary energy, protein, and calcium intakes were correlated with BMD at the lumbar spine. Stepwise multiple linear regression analyses showed that age, BMI, and physical activity were significant predictors for BMD at all sites. In addition, energy intake was also a predictor for BMD at the lumbar spine. The protein intake was associated with BMD at the spine (P = 0.02 and beta = 0.163) even after making adjustments for energy intake. Thus, dietary pattern coupled with higher education levels and greater physical activity favored bone health.

Vitamin D insufficiency: disease or no disease?

Vitamin D insufficiency (VDI) is widely reported. In patients with normal PTH, the diagnosis rests on increases in fractional calcium absorption (FCA) when 25(OH)D increases above 30 ng/ml. However, estimates of increased FCA after correction of VDI vary dramatically, depending on study methods. We used a dual stable calcium isotope to clarify the impact of vitamin D repletion on FCA in postmenopausal women with VDI. We hypothesized that FCA would increase with vitamin D repletion. We studied postmenopausal women with VDI [25(OH)D = 16-24 ng/ml] and an estimated calcium intake <or=1100 mg daily. Exclusion criteria included hypercalcemia, hypercalciuria, renal insufficiency, nephrolithiasis, gastrointestinal disorders, osteomalacia, prior adult fragility fracture, baseline T-score < -3.0, and use of medications known to interfere with vitamin D or calcium metabolism. Each woman underwent inpatient FCA studies before and after correction of VDI. We used ergocalciferol 50,000 IU/d for 15 days to achieve vitamin D repletion. During each study, women consumed their typical diet. They ingested (44)Ca orally with breakfast and received (42)Ca intravenously. We collected urine for 24 h and measured its calcium isotope content by mass spectrometry. Eighteen women completed the study; all but two had normal PTH. During the first and second FCA studies, their mean 25(OH)D level was 22 +/- 4 and 64 +/- 21 ng/ml, respectively (p < 0.001). Subjects' average FCA was 24 +/- 7% initially and 27 +/- 6% after vitamin D repletion (p = 0.04). Thus, FCA increased by 3 +/- 1% with correction of VDI. Postmenopausal women with VDI experience small FCA increments with vitamin D therapy. In existing literature, this small change in FCA does not associate with lower fracture rates or consistently higher bone mass. Future studies should ascertain whether small FCA increments favorably affect the skeleton.

Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca

INTRODUCTION

The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments.

METHODS

Thirteen postmenopausal women (>or=6 yr since menopause) were predosed with 41Ca iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for 41Ca/Ca analysis by accelerator mass spectrometry.

RESULTS

Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary 41Ca/Ca ratios.

CONCLUSIONS

Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary 41Ca excretion from prelabeled bone.

Protein consumption is an important predictor of lower limb bone mass in elderly women

BACKGROUND

The effect of protein intake on bone density is uncertain, and evidence exists for beneficial effects of both low and high protein intakes.

OBJECTIVE

The objective was to study the relation between protein consumption and bone mass in elderly women with allowance for other lifestyle factors affecting bone metabolism.

DESIGN

We conducted a cross-sectional and longitudinal study of a population-based sample of 1077 women aged 75 +/- 3 y. At baseline, protein consumption was measured with a food-frequency questionnaire, and bone mass and structure were measured by using quantitative ultrasound of the heel. One year later, hip bone mineral density (BMD) was measured by using dual-energy X-ray absorptiometry.

RESULTS

Subjects consumed a mean (+/-SD) of 80.5 +/- 27.8 g protein/d (1.19 +/- 0.44 g protein/kg body wt). Regression analysis showed a positive correlation between protein intake and qualitative ultrasound of the heel and BMD after adjustment for age, body mass index, and other nutrients. The dose-response effect was best characterized by protein consumption expressed in tertiles, such that subjects in the lowest tertile (<66 g protein/d) had significantly lower qualitative ultrasound of the heel (1.3%) and hip BMD (2.6%) than did the subjects in the higher tertiles (>87 g protein/d).

CONCLUSION

These data suggest that protein intakes for elderly women above current recommendations may be necessary to optimize bone mass.

A longitudinal study of bone-related biochemical changes at the menopause

OBJECTIVE

To evaluate the effects of the menopause on bone-related biochemical variables in a longitudinal study.

DESIGN

Recruitment by advertisement of premenopausal women over the age of 44 for measurement of selected variables and collection of blood and urine samples for deep freezing, followed by annual check of menopausal status and repeat collection of blood and urine samples for deep freezing after the menopausal transition.

PATIENTS

A total of 104 women with confirmed premenopausal status and on no treatment likely to affect calcium or bone metabolism were admitted to the study over a period of 2 years. After 8 years, 43 of the volunteers had passed through the menopause and the study was closed.

MEASUREMENTS

Radiocalcium absorption was measured at the first attendance and again after the menopausal transition. Calcium and other relevant variables were measured consecutively on paired thawed-out samples of blood and urine.

RESULTS

The data were complete in 34 subjects. In these women, there were highly significant correlations between the first and second measurements of most variables - serum calcium and fractions, radiocalcium absorption, vitamin D metabolites, PTH and others - indicating significant 'tracking' of these variables across the menopause. Within that framework there were significant rises in serum total and calculated ionized calcium (both P < 0.001) without change in mean serum parathyroid hormone (PTH). Radiocalcium absorption fell (P < 0.001) without change in serum 1,25D. There was a rise in fasting urinary calcium (P < 0.001) which could not be explained by the rise in filtered load and therefore represented a fall in TmCa (P < 0.001). There were significant rises in urinary bone resorption markers, pyridinoline and deoxypyridinoline (P < 0.001).

CONCLUSIONS

We conclude that the menopausal rise in calculated serum ionized calcium without fall in PTH, indicates a change in PTH set-point, and that the falls in gastrointestinal absorption and renal tubular reabsorption of calcium reflect the loss of an oestrogen action at these two sites. Although these changes are sufficient to explain the rise in calcium requirement at the menopause, the association of high bone resorption with normal serum PTH suggests also an increased sensitivity of bone to the action of parathyroid hormone. There is significant 'tracking' of many variables across the menopause despite very significant changes in their absolute values.

Relation between calcium absorption and serum calcitriol in normal men: evidence for age-related intestinal resistance to calcitriol

OBJECTIVE

To obtain information on the causes of age-related bone loss in men and the concomitant decline in calcium absorption.

DESIGN

Cross-sectional study.

SETTING

Adelaide, South Australia, Australia.

SUBJECTS

A total of 95 healthy, Caucasian men (age range 27-87 y).

RESULTS

Calcium absorption declined with age (r=-0.46, P<0.0001), as did 24-h urine calcium, phosphate and creatinine (r>-0.21, P<0.05 for all); serum calcitriol and 25 hydroxyvitamin D did not change with age. Calcium absorption was related to serum calcitriol (r=0.20, P=0.05). An inverse relation between the residual deviations in calcium absorption, after allowing for its dependence on calcitriol, and age (F=5.4, P<0.005) was observed. The 24-h urinary calcium, phosphate and creatinine were all related to calcium absorption (r>0.41, P<0.0001). Forearm bone density fell with age (r=-0.45, P<0.0001) but was not related to calcium absorption, or markers of bone turnover.

CONCLUSIONS

In healthy Caucasian males (i) calcium absorption falls, but serum calcitriol does not change with age, (ii) the relation between calcium absorption and serum calcitriol changes with age, indicative of an intestinal resistance to calcitriol and (iii) calcium absorption is a significant determinant of 24-h urinary calcium excretion.

Soy protein has a greater effect on bone in postmenopausal women not on hormone replacement therapy, as evidenced by reducing bone resorption and urinary calcium excretion

Recent reports suggest that soy protein may reduce the risk of osteoporosis in peri- and postmenopausal women. The objective of this study was to examine whether soy supplementation exerts beneficial effects on serum and urinary biomarkers of bone metabolism in postmenopausal women, regardless of whether or not they are on hormone replacement therapy (HRT). A total of 71 women were randomly assigned to either soy protein (SP) or milk-based protein (MBP), 40 g daily for 3 months, in a double-blind parallel design. Forty-two women completed the study (20 on SP and 22 on MBP). Overall, both protein supplements positively influenced serum IGF-I, known to correlate with bone formation. However, SP had a more pronounced effect on IGF-I than MBP. Urinary deoxypyridinoline (Dpd) excretion, a specific biomarker of bone resorption, was significantly reduced by SP, but not by MBP when all women were included. Furthermore, women on MBP experienced a 33% increase in urinary calcium excretion, whereas SP did not have such an effect. To evaluate whether SP affects women differently on the basis of their HRT status, data from women on HRT (n = 22) and those not on HRT (n = 20) were analyzed separately. The subanalysis of the data indicated that SP had the greatest impact on serum IGF-I (an increase of 97%) in the women not on HRT. The changes in urinary Dpd due to SP were only observed in women not on HRT, indicating that the overall decrease in Dpd occurred with SP in the absence of HRT. These results indicate that soy protein may positively influence bone and calcium homeostasis in postmenopausal women, particularly those not on HRT.

Lactose does not enhance calcium bioavailability in lactose-tolerant, healthy adults

BACKGROUND

There is evidence from animal studies that lactose has a beneficial effect on intestinal calcium absorption. However, data concerning the effect of lactose on calcium absorption in lactose-tolerant adults are inconclusive.

OBJECTIVE

Our objective was to investigate the effect of lactose on calcium bioavailability in humans by the use of a stable-strontium test under controlled metabolic conditions.

DESIGN

Eleven healthy, lactose-tolerant subjects (8 women, 3 men) randomly received a bolus of 2.27 mmol strontium alone (load A), the bolus with 35 g lactose (load B), or the bolus with 17.5 g glucose and 17.5 g galactose (load C). Blood samples were drawn at 0, 15, 30, 60, 90, 180, 240, and 300 min. Urine specimens were collected during the time intervals -2 to 0, 0-2, 2-4, 4-6, and 6-24 h.

RESULTS

Pharmacokinetic parameters of strontium bioavailability were comparable for all 3 loads. In detail, fractional absorption at 240 min for loads A, B, and C was 12.1 +/- 0.7%, 13.0 +/- 1.1%, and 12.2 +/- 0.7%, respectively. Areas under the curve for 0-240 min were 70.8 +/- 6.3, 69.6 +/- 3.5, and 65.8 +/- 5.1 micromol*h/L for loads A, B, and C, respectively (NS). Moreover, fractional strontium excretion values of 5.1 +/- 0.8% (load A), 5.8 +/- 0.4% (load B), and 5.2 +/- 0.8% (load C) were not significantly different.

CONCLUSIONS

Lactose does not have a beneficial effect on calcium bioavailability in lactose-tolerant adults.

A 4-year follow-up study of the effects of calcium supplementation on bone density in elderly postmenopausal women

To determine the long-term effect of calcium supplementation on bone density, 84 elderly women (54-74 years) more than 10 years past the menopause were studied for 4 years as part of a follow-up study of a randomized, double-masked, placebo-controlled trial. The placebo group who did not take calcium supplements at all during the 4-year study (control group, n = 21) served as a comparison with the treated group who took calcium supplements for 4 years (calcium supplement group, n = 14). We also studied subjects who were treated for 2 years with calcium supplements and then ceased taking them (non-compliant group, n = 49). The changes in bone density at the lumbar spine, hip and ankle sites, current calcium intake and activity were monitored. Over the 4 years the calcium supplement group (mean calcium intake 1988 +/- 90 mg/day) did not lose bone at the hip and ankle site. The control group (mean calcium intake 952 +/- 109 mg/day) lost significantly more bone than the calcium supplement group at all sites of the hip and ankle. No overall bone loss was seen at the spine, in either group, over the 4 years of this study. Between years 2 and 4 the non-compliant group (mean calcium intake 981 +/- 75 mg/day) lost significantly more bone at all sites of the ankle than the calcium supplement group. Therefore, calcium supplementation produces a sustained reduction in the rate of loss of bone density at the ankle and hip sites in elderly postmenopausal women. Increasing dietary calcium intake in women should be the aim of a public health campaign.

[Determination of intestinal strontium absorption--assessment and validation of routinely manageable test procedures]

Intestinal strontium absorption has been discussed recently as an indirect measure for calcium uptake. Prerequisite for the clinical use of an oral strontium test is the availability of a reliable procedure including controlled strontium supply, sample pretreatment and analysis as well as the assessment of normal values. In the present study, a group of young females (n = 33; 24.0 +/- 2.7 y; BMI 21.5 +/- 1.9) received an oral dose of 2.27 mmol strontium in a standardized breakfast that contained 0.625 mmol calcium. Before and 220 min after the bolus serum strontium concentrations were determined by means of atomic absorption spectrophotometry (coefficient of variation: within day 4.8%, n = 10; day-to-day 9.5%, n = 8). The error of the method was 2.7%. Calculation of the fractional strontium absorption rate considered the respective distribution volume (extracellular fluid; either estimated using body weight or determined by means of bioimpedance analysis [BIA]). Average absorption rates were 13.3 +/- 3.1% and, considering BIA measurement 13.6 +/- 2.6%, respectively. Smoking, exercise and, use of oral contraceptives showed no effects. Our oral strontium test is characterized by excellent reliability, easy handling and low costs and, thus, is suitable for routine use.

Measurement of bone resorption by strontium excretion in prelabelled rats

The body handles strontium (Sr) in a similar way to calcium (Ca) in that Sr is absorbed by the gut, concentrated in bone and excreted in urine and feces. In this study, rats were labelled with Sr during growth and later subjected to various treatments affecting bone resorption and Sr excretion was measured during and after treatment. Six weeks old Wistar rats were repeatedly s.c. injected with SrCl2. After a period of 2 weeks after the last Sr injection the rats were subjected to various treatments. Sr clearance was then measured weekly for 2 weeks. In the first experiment, the Sr labelled rats were sham-operated (sham) or ovariectomized (ovx) and urine collected afterwards. Sham rats were either treated with 4 daily s.c. clodronat injections at the beginning of the urine sampling, fed a low Ca diet (0.08% Ca) during the second sampling week or injected with saline. Urinary Sr excretion was decreased in the clodronate group during the first sampling week and increased in the Ca depleted group during feeding the low Ca diet. Sr excretion by ovx rats was similar to the sham control. In the second experiment, the effect of high-dose treatment with 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) or clodronate on bone resorption induced by Ca depletion was assessed by Sr output in urine and feces. Sr labelled rats were fed a low Ca diet and daily injected with 24,25(OH)2D3 or clodronate for 14 consecutive days. Clodronate significantly decreased Sr output during both sampling weeks. Treatment with 24,25(OH)2D3 resulted in an increased Sr output indicating an increase in bone resorption.

The effects of calcium supplementation (milk powder or tablets) and exercise on bone density in postmenopausal women

The etiology of age-related bone loss is unclear but both lack of exercise and dietary calcium deficiency have been implicated in its causation. This 2-year randomized placebo-controlled study was designed to examine the effects of increased dietary calcium and exercise in 168 women who were more than 10 years postmenopausal. The subjects were randomized into one of 4 groups: placebo, milk powder containing 1 g of calcium, calcium tablets 1 g/night, and calcium tablets 1 g/night and an exercise regimen. The exercise group aimed to undertake 4 h of extra weight-bearing exercise per week and were undertaking 10% more activity than other groups at 2 years. Bone mineral density at the lumbar spine, three hip sites, and two sites of the tibia close to the ankle joint were measured at 6 month intervals. Dietary intake was evaluated by a weighed food record, exercise was evaluated by an exercise diary, and blood and urine samples were obtained to examine effects on calcium homeostasis. Individual data points were compared using repeated measures ANOVA and least squares regression. Calcium supplementation by either the calcium tablets or the milk powder resulted in cessation of bone loss at the intertrochanteric hip site (placebo, calcium tablets, calcium and exercise, milk powder -0.81, +0.17, +0.23, and +0.07% per year, respectively; p < 0.05 for all supplementation groups compared with placebo) with similar results at the trochanteric hip site. The calcium and exercise group had less bone loss at the femoral neck site when compared with calcium supplementation alone (placebo, calcium tablets, calcium and exercise, milk powder -0.67, -0.18, +0.28, and -0.18% per year, respectively; p < 0.05 for calcium and exercise compared with calcium alone). There was a significant reduction in the rate of bone loss at the ultradistal site of the tibia (placebo, calcium tablets, calcium and exercise, milk powder -2.5, -1.6, -1.0, and -1.5% per year, respectively; p < 0.05 for all supplementation groups compared with placebo). There was no significant bone loss at the spine site in any group.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of menopause and age on calcitropic hormones: a cross-sectional study of 655 healthy women aged 35 to 90

Although women lose 30% of their skeletal mass after the menopause, the mechanism of this loss is uncertain. Clearly estrogen deficiency is important but whether this works only through direct effects on the skeleton is uncertain. To examine these mechanisms further we have evaluated calcium-related metabolic factors in 655 healthy women. Fasting blood samples were collected from all subjects who were up to 35 years past the menopause, and fasting urine and 24-h urine samples were collected in 365 women who were up to 25 years past the menopause. In the first 15 years postmenopause, there was a rise in total plasma calcium due to a rise in albumin. Bone resorption (hydroxyproline creatinine ratio), bone formation (alkaline phosphatase), and the urine calcium creatinine ratio all rose at menopause and remained elevated for the next 25 years. There was a transient further rise in bone resorption for the 10 years following menopause. Neither PTH nor the free calcitriol index changed for the first 10 years following menopause. Ten years past the menopause, although total calcitriol rose, the free calcitriol index fell due to a rise in vitamin D binding protein. PTH began to rise at 15 years past menopause. GFR fell gradually over the 25 years following menopause. Thus following menopause there is an increase in bone turnover and increased urine calcium loss independent of any effect of PTH or calcitriol, suggesting a direct effect of estrogen deficiency on bone and kidney.(ABSTRACT TRUNCATED AT 250 WORDS)