Mary Crutchfield

Bone Mineral Density and Its Change in White Women: Estrogen and Vitamin D Receptor Genotypes and Their Interaction

Low bone mineral density (BMD) is a major risk factor for development of osteoporosis; increasing evidence suggests that attainment and maintenance of peak bone mass as well as bone turnover and bone loss have strong genetic determinants. We examined the association of BMD levels and their change over a 3‐year period, and polymorphisms of the estrogen receptor (ER), vitamin D receptor (VDR), type I collagen, osteonectin, osteopontin, and osteocalcin genes in pre‐ and perimenopausal women who were part of the Michigan Bone Health Study, a population‐based longitudinal study of BMD. Body composition measurements, reproductive hormone profiles, bone‐related serum protein measurements, and life‐style characteristics were also available on each woman. Based on evaluation of women, ER genotypes (identified by PvuII [n = 253] and XbaI [n = 248]) were significantly predictive of both lumbar spine (p < 0.05) and total body BMD level, but not their change over the 3‐year period examined. The VDR BsmI restriction fragment length polymorphism was not associated with baseline BMD, change in BMD over time, or any of the bone‐related serum and body composition measurements in the 372 women in whom it was evaluated. Likewise, none of the other polymorphic markers was associated with BMD measurements. However, we identified a significant gene × gene interaction effect (p < 0.05) for the VDR locus and PvuII (p < 0.005) and XbaI (p < 0.05) polymorphisms, which impacted BMD levels. Women who had the (−/−) PvuII ER and bb VDR genotype combination had a very high average BMD, while individuals with the (−/−) PvuII ER and BB VDR genotype had significantly lower BMD levels. This contrast was not explained by differences in serum levels of osteocalcin, parathyroid hormone, 1,25‐dihydroxyvitamin D, or 25‐dihydroxyvitamin D. These data suggest that genetic variation at the ER locus, singly and in relation to the vitamin D receptor gene, influences attainment and maintenance of peak bone mass in younger women, which in turn may render some individuals more susceptible to osteoporosis than others.

The associations of bone mineral density and bone turnover markers with osteoarthritis of the hand and knee in pre- and perimenopausal women

OBJECTIVE To determine whether Caucasian women ages 28-48 years with newly defined osteoarthritis (OA) would have greater bone mineral density (BMD) and less bone turnover over time than would women without OA. METHODS Data were derived from the longitudinal Michigan Bone Health Study. Period prevalence and 3-year incidence of OA were based on radiographs of the dominant hand and both knees, scored with the Kellgren/Lawrence (K/L) scale. OA scores were related to BMD, which was measured by dual-energy x-ray absorptiometry, and to serum osteocalcin levels, which were measured by radioimmunoassay. RESULTS The period prevalence of OA (K/L grade > or =2 in the knees or the dominant hand) was 15.3% (92 of 601), with 8.7% for the knees and 6.7% for the hand. The 3-year incidence of knee OA was 1.9% (9 of 482) and of hand OA was 3.3% (16 of 482). Women with incident knee OA had greater average BMD (z-scores 0.3-0.8 higher for the 3 BMD sites) than women without knee OA (P < 0.04 at the femoral neck). Women with incident knee OA had less change in their average BMD z-scores over the 3-year study period. Average BMD z-scores for women with prevalent knee OA were greater (0.4-0.7 higher) than for women without knee OA (P < 0.002 at all sites). There was no difference in average BMD z-scores or their change in women with and without hand OA. Average serum osteocalcin levels were lower in incident cases of hand OA (>60%; P = 0.02) or knee OA (20%; P not significant). The average change in absolute serum osteocalcin levels was not as great in women with incident hand OA or knee OA as in women without OA (P < 0.02 and P < 0.05, respectively). CONCLUSION Women with radiographically defined knee OA have greater BMD than do women without knee OA and are less likely to lose that higher level of BMD. There was less bone turnover among women with hand OA and/or knee OA. These findings suggest that bone-forming cells might show a differential response in OA of the hand and knee, and may suggest a different pathogenesis of hand OA and knee OA.

Genetic Markers, Bone Mineral Density, and Serum Osteocalcin Levels

We evaluated five genetic markers for products that contribute to skeletal mineralization including the Sp1 polymorphism for type I collagen Ai (COLIA1), the vitamin D receptor (VDR) translation initiation site polymorphism, the promoter of the osteocalcin gene containing a C/T polymorphism, the estrogen receptor (ER) gene containing a TA repeat, and the polymorphic (AGC)n site in the androgen receptor. These markers were evaluated for their potential relationship with bone mineral density (BMD), measured by dual‐energy X‐ray densitometry, or its 3‐year change. Additionally, potential associations of these genotypes and with baseline osteocalcin concentration or its 3‐year change (assessed using radioimmunoassay) were evaluated. The study was conducted in 261 pre‐ and perimenopausal women of the Michigan Bone Health Study, a population‐based longitudinal study of musculoskeletal characteristics and diseases. The polymorphic (AGC)n site in the androgen receptor showed a strong association with BMD of the femoral neck (FN) and lumbar spine and remained highly significant after adjusting for body mass index (BMI), oophorectomy/hysterectomy, oral contraceptive (OC) use and hormone replacement use (p < 0.001). The TA repeat at the 5′ end of the ER gene was associated with total body calcium (p < 0.05) after adjusting for BMI, oophorectomy and hysterectomy, and OC use. The frequency of oophorectomy and hysterectomy within selected genotypes explained much of the statistically significant association of the ER genotypes with BMD of the FN and spine. There was no association of measures of BMD or bone turnover with the Sp1 polymorphism for COLIA1, the VDR translation initiation site polymorphism, or the C/T promoter polymorphism of the osteocalcin gene. These findings suggest that sex hormone genes may be important contributors to the variation in BMD among pre‐ and perimenopausal women.

Bone Mineral Density and Its Change in Pre‐ and Perimenopausal White Women: The Michigan Bone Health Study

There is a need to better understand potential bone mineral density (BMD) loss during the menopausal transition since this period may include the initiation of interventions. The study purpose was to determine if there was BMD loss at the femoral neck, lumbar spine, or total body bone sites in a population‐based study of women approaching or transitioning the midlife. The 583 enrollees were 25–45 years of age at the first of four annual measurements from 1992 through 1996. Bone mineral content and bone width were measured using dual‐energy X‐ray absorptiometry. Considering all enrollees collectively, there was a significant 3‐year decline (1%) in BMD at the femoral neck over the 3‐year period (p = 0.0076). There was no significant annual change in the lumbar spine (p = 0.11), and a significant annual increase in the total body BMD (p = 0.0003). Within subgroups and cross‐sectionally, BMD values of the femoral neck were 5% lower in women classified as perimenopausal compared with premenopausal enrollees; BMD was 3% and 1% lower at the lumbar spine and total body sites, respectively. Longitudinally, among perimenopausal women, a double oophorectomy was associated with BMD loss in the spine (p = 0.0003), even though 75–85% of these women had a hormone replacement prescription at some time during the study period. In summary, the site with evidence of loss was the femoral neck, specifically among perimenopausal women. There was little evidence of substantial total body or lumbar spine BMD loss in premenopausal women with ovaries who maintained follicle‐stimulating hormone levels < 20 mIU/l in the early follicular period. Double oophorectomy, even with hormone replacement, was associated with bone loss.

Familiality and partitioning the variability of femoral bone mineral density in women of child-bearing age

SummaryThe contributions of polygenic loci and environmental factors to femoral bone mineral density (BMD in g/cm2) variability were estimated in modified family sets consisting of women of child-bearing age. Femoral BMDs were measured in 535 women who were members of 137 family sets consisting minimally of an index, her sister, and unrelated female control. The family set could also include multiple sisters and first cousins. Women included in these family sets were all between 20 and 40 year of age to minimize the cohort effects of maturation and menopause on measures of BMD. BMDs were measured at three femoral sites using dual photon densitometry. Values were regressed on age and Quetelet Index which explained 13–15% of the variability in BMD (dependent on site). Subsequent variance components analysis on the residuals indicated that unmeasured polygenic loci accounted for substantial additional variability: 67% for femoral neck, 58% for Wards triangle, and 45% for trochanter. These results suggest that polygenic loci account for approximately half of the variability in maxmal femoral BMD.

Urinary Ovarian and Gonadotropin Hormone Levels in Premenopausal Women with Low Bone Mass

We hypothesized that lower ovarian and gonadotropin hormone concentrations would be associated with lower levels of peak bone mineral density (BMD) in apparently normally menstruating women who did not exercise intensively and did not report anorexia or bulimia. This hypothesis was evaluated using a case‐with‐control study design (n = 65) which was nested within a population‐based longitudinal study of peak bone mass (Michigan Bone Health Study) with annual assessment in women aged 25–45 years (n = 582). Cases were 31 premenopausal women with BMD of the lumbar spine, femoral neck, and total body less than the 10th percentile of the distribution, where controls were 34 premenopausal women with BMD between the 50th and 75th percentile. BMD was measured by dual‐energy X‐ray absorptiometry. In addition to their annual measurements, these 65 participants collected first‐voided morning urine specimens daily through two consecutive menstrual cycles. The urine from alternating days of this collection was analyzed for estrone‐3‐glucuronide (E1G), pregnanediol glucuronide (PdG), testosterone, and follicle‐stimulating hormone by radioimmunoassay and these values adjusted for daily creatinine excretion levels. Additionally, analyses of daily urine specimens for luteinizing hormone (uLH) was undertaken to better characterize the possible uLH surge. Cases had significantly lower amounts of E1G (p = 0.009) and PdG (p = 0.002) than did controls, whether amounts were characterized by a mean value, the highest value, or the area under the curve, and after statistically controlling for body size. Further, when B‐splines were used to fit lines to the E1G and PdG data across the menstrual cycle, the 95% confidence intervals (CIs) about the line for the controls consistently excluded and exceeded the 95% confidence bands for the cases in the time frame associated with the luteal phase in ovulatory cycles. Likewise, 95% CIs for the LH surge in controls exceeded the fitted line for cases around the time associated with the LH surge. The cases and controls were not different according to dietary intake (energy, protein, calcium), family history of osteoporosis, reproductive characteristics (parity, age at menarche, age of first pregnancy), follicular phase serum hormone levels, calciotropic hormone levels, or by evidence of perimenopause. We conclude that these healthy, menstruating women with BMD at the lowest 10th percentile from a population‐based study had significantly lower urinary sex steroid hormone levels during the luteal phase of menstrual cycles as compared with hormone levels in premenopausal women with BMD between the 50th and 75th percentile of the same population‐based study, even after considering the role of body size. These data suggest that subclinical decreases in circulating gonadal steroids may impair the attainment and/or maintenance of bone mass in otherwise reproductively normal women.

Body composition, age and femoral bone mass of young adult women

Maximum bone mineral density of the femur was measured by dual-photon densitometry in 282 healthy white women, aged 20 to 40 years. Femoral sites included the neck, Wards triangle, and the trochanter. Quetelet Index was used as a measure of weight adjusted for height, and body composition was measured using four-point bioelectrical impedance and anthropometry. Maximum bone mass is believed to be an important measure if the level established which remain characteristic or predict bone mineral density during the aging process. Body weight was correlated with each measure of femoral bone density, including the femoral neck (r = .42), Wards triangle (r = .34), and the trochanter (r = .44). Weight was more highly correlated with bone mass than with other measures of body composition, including fat-free mass, percent body fat, humeral muscle area, and humeral fat area. We observed that age was negatively associated with bone mass at all three femoral sites, even in subjects within the age range of 20 to 40 years, and the relationship was significant after controlling for Quetelet Index. There was no evidence of a nonlinear relationship that would indicate when maximal femoral bone mass reaches its peak within this age range.

LONGITUDINAL CHANGES IN BODY COMPOSITION IN WOMEN APPROACHING THE MIDLIFE

This population-based longitudinal study describes the 4.5-year changes in body composition and body mass distribution in women aged 20-45 years, and characterizes predictors of these changes. Body weight, waist-to-hip ratio, Quetelet index, fat and lean body mass were measured in 404 white menstruating women aged 20-40 at baseline and 4.5 years later (follow-up). Variables considered for predicting body composition differences were hormonal status, menstrual status, parity, diet and physical activity. Average body weight increased 4.3 kg in 4.5 years (6.4 kg increase in fat and 2.1 kg decrease in lean)--a net increase of 7.1% total body fat. Measured predictors were not significantly associated with weight or Quetelet index; however, they were associated with measured amounts of lean and fat. Longitudinally, women who preserved the most lean body mass tended to be nulliparous, to be still menstruating, to have higher testosterone levels, and to smoke. Physical activity was associated with preserving lean body mass. Increasing age and higher follicle-stimulating hormone levels were associated with increasing waist-to-hip ratio. Average body weight showed a steady increase--characterized by an expanding fat compartment and a shrinking lean compartment--with the older women increasing more in waist girth relative to hip girth than younger women. Predictor variables of these changes included hormonal environment, physical activity, smoking behaviour, parity, and oophorectomy.

Elevated parathyroid hormone-related peptide associated with lactation and bone density loss

OBJECTIVE To investigate the hypothesis that parathyroid hormone-related peptide (PRHrP) may be involved with bone loss and recovery as a means of providing adequate calcium and phosphate to infants. DESIGN An 18-month prospective cohort study. SETTING General community setting with recruitment occurring at birthing education classes. PARTICIPANTS Volunteer sample of 115 postpartum healthy women aged 20 to 40 years, and 0 or 1 parity prior to parturition with no intent to breast-feed or intent to breast-feed at least 6 months. MAIN OUTCOME MEASURES Parathyroid hormone-related peptide, prolactin, estradiol, 1,25-dihydroxyvitamin D, 24-hydroxyvitamin D, femoral bone mineral density, and bone turnover markers were measured in 115 postpartum women at 2 weeks, 2 months, 4 months, 6 months, 12 months, and 18 months postpartum. Lumbar bone mineral density was measured at 2 weeks, 6 months, 12 months, and 18 months postpartum. RESULTS Elevated PTHrP values were significantly associated (P<.001) with breast-feeding status, elevated prolactin levels, and lower serum estradiol levels, conditions occurring during lactation. Furthermore, elevated PTHrP levels were negatively and significantly associated (P<.01) over time with bone mineral density change at both the spine and the femoral neck, even after accounting for prolactin levels, breast-feeding status, return of menstruation, estradiol levels, PTH levels, 1,25-dihydroxyvitamin D levels, dietary calcium intake, physical activity, and body size. CONCLUSION These data clearly support the hypothesis that PTHrP is an alternative mechanism associated with bone loss and recovery during and subsequent to lactation.