Michelle E. Danielson

Serum 25-Hydroxyvitamin D Concentrations and Risk for Hip Fractures

Context Vitamin D supplementation may help prevent fractures, but the relationship between blood vitamin D concentrations and fracture risk is unclear. Contribution These authors observed an increased risk for hip fracture among women with lower serum 25-hydroxyvitamin D [25(OH) vitamin D] concentrations that was independent of measures of frailty, body mass index, physical function, and falls. Caution The authors did not measure bone mineral density (BMD), so they could not determine whether 25(OH) vitamin D concentrations give different information about fracture risk than that offered by BMD. Implication Low serum 25(OH) vitamin D concentrations seem to be associated with a higher hip fracture risk. The Editors Vitamin D deficiency is common in older adults, especially during the winter (1) and in homebound populations (2), general medical inpatients (3), and community-dwelling women admitted to the hospital with acute hip fracture (4). A recently published evidence-based report on vitamin D and bone health (5) found the level of evidence for an association between serum 25-hydroxyvitamin D [25(OH) vitamin D] concentrations and fracture risk to be inconsistent (5). Since publication of that review, 1 prospective study (6) reported no relationship between serum 25(OH) vitamin D concentrations and fractures, whereas another (7) reported a significantly lower risk for hip fracture with 25(OH) vitamin D concentrations greater than 60 nmol/L. Vitamin D concentration could be associated with fractures in several ways. It could influence muscle strength and balance, both of which contribute to falls and disability (810). The association between 25(OH) vitamin D concentrations and fracture may also be influenced by renal function, because renal insufficiency has been linked to fracture (11) and to vitamin D deficiency (12). Several interactions between vitamin D and estrogen receptors have been described (13); hormone therapy has been shown to reverse abnormalities in vitamin D metabolism (14), and low vitamin D concentrations have also been linked to higher bone turnover (15, 16). Thus, sex-steroid hormones and bone turnover could contribute to the association between 25(OH) vitamin D concentration and fractures. We conducted a nested casecontrol study within the WHI-OS (Womens Health Initiative Observational Study) among 400 case-patients with adjudicated incident hip fracture and 400 control participants. We tested whether low serum 25(OH) vitamin D concentrations are associated with a higher risk for hip fractures in community-dwelling women and whether this relationship may be mediated by poor physical functioning, frailty, falls, sex-steroid hormones, renal function, or bone turnover. Methods Study Population Our study population came from the WHI-OS, a prospective cohort study that enrolled 93676 women between 1994 and 1998 at 40 U.S. clinical centers (age range, 50 to 79 years). Study methods are described in detail elsewhere (17). In brief, women were eligible if they were postmenopausal, were unlikely to move or die within 3 years, were not enrolled in the WHI clinical trials, and were not currently participating in any other clinical trial. The human subjects review committees from each participating institution approved the study. Follow-up and Outcome Ascertainment We sent women questionnaires annually to report any hospitalization and other outcomes, including fractures. As of August 2004, median follow-up duration was 7.1 years (range, 0.7 to 9.3 years). At that time, 3.7% of participants had withdrawn or were lost to follow-up and 5.3% had died. We reviewed medical records to verify cases of hip fracture, and blinded central adjudicators confirmed the cases (18). We excluded patients with pathologic hip fractures. Nested CaseControl Study Design The present study is a casecontrol study nested within the prospective design of WHI-OS. We excluded women who had a history of hip fracture; were receiving hormone therapy up to 1 year before enrollment; or were currently receiving androgens, selective estrogen receptor modulators, antiestrogens, or other osteoporosis treatments (bisphosphonates, calcitonin, or parathyroid hormone). We also excluded women with insufficient serum stored or of unknown ethnicity, leaving 39793 eligible participants. Of these, 404 women had a hip fracture. We randomly selected 400 of these women to form the incident hip fracture group. For each case-patient, we selected 1 control participant who was within 1 year of the case-patients age at screening, was of matching race or ethnicity, and had their blood drawn within 120 days of the case-patients blood draw date; 99% of case-patients and control participants were matched within 30 days. Baseline Clinical Variables We divided clinical centers into 3 geographic regions on the basis of latitude: northern (>40 N), middle (35 to 40 N), and southern (<35 N). We ascertained all covariates at baseline. Clinic interviewers recorded current use of prescription medications by direct inspection of medicine containers. We entered prescription names into the WHI database and assigned drug codes by using Medispan software (First DataBank, San Bruno, California). Average amounts of elemental calcium and vitamin D preparations were entered directly from supplement containers. Dietary intakes of calcium and vitamin D were assessed by using a semiquantitative food-frequency questionnaire (19). Total calcium and vitamin D intake was defined as the sum of diet and supplements. We used questionnaires to ascertain date of birth, race or ethnicity, age at menopause, history of any fracture after age 55 years, smoking, parental history of hip fracture, self-rated health status, and alcohol consumption. We classfied physical activity on the basis of frequency and duration of walking and mild, moderate, and strenuous activities in the previous week. We calculated kilocalories of energy expended in 1 week as the metabolic equivalent (kcal hours/week per kg) (20). We measured physical function by using the RAND Short Form-36 physical function scale, which comprises 10 items measuring whether health now limits physical function in moderate or vigorous activity (2 items); strength to lift, carry, stoop, bend, or stair climb (4 items); ability to walk various distances without difficulty (3 items); and self-care (1 item) (21). The scale is scored from 0 to 100, with higher scores indicating better physical function. We compared women with a score greater than 90 versus those with a score less than or equal to 90, a cutoff value corresponding to the median score. We computed a frailty score, which included self-reported muscle weakness and impaired walking speed (RAND Short Form-36 physical function scale score <75), exhaustion (RAND Short Form-36 vitality scale score <55), low physical activity (lowest quartile of physical activity), and unintended weight loss between baseline and 3 years of follow-up (22). A woman was considered frail if she reported 3 or more of these indicators. Weight was measured on a balance-beam scale with the participant dressed in indoor clothing without shoes. Height was measured by using a wall-mounted stadiometer. Body mass index was calculated as weight (in kg) divided by height (in m2). Laboratory Procedures Laboratory personnel blinded to casecontrol status obtained a 12-hour fasting blood sample at the baseline visit, which was processed and stored at 80C according to strict quality control procedures (23). Serum 25(OH) vitamin D concentrations and sex-steroid hormone levels were measured at the Reproductive Endocrine Research Laboratory at the University of Southern California. 25-Hydroxyvitamin vitamin D was measured by using a radioimmunoassay with DiaSorin reagents (DiaSorin, Stillwater, Minnesota). The sensitivity of the assay was 3.75 nmol/L. The interassay coefficients of variation were 11.7%, 10.5%, 8.6%, and 12.5% at 14.0, 56.8, 82.5, and 122.5 nmol/L, respectively. Estradiol and testosterone concentrations were quantified by using sensitive and specific radioimmunoassays after organic solvent extraction and celite column partition chromatography (2427). The intra- and interassay coefficients of variation were 7.9% and 8% to 12%, respectively, for estradiol and 6% and 10% to 12%, respectively, for testosterone. We calculated bioavailable hormone concentrations by using mass action equations (2830). We measured sex hormonebinding globulin by using a solid-phase, 2-site chemiluminescent immunoassay. The intra- and interassay coefficients of variation were 4.1% to 7.7% and 5.8% to 13%, respectively. Serum cystatin C, a marker of renal function that is independent of age and weight, was measured at Medical Research Laboratories International, Highland Heights, Kentucky, by using the Dade Behring BN-II nephelometer and Dade Behring reagents (Dade Behring, Ramsey, Minnesota) in a particle-enhanced immunonepholometric assay. Serum C-terminal telopeptide of type I collagen and aminoterminal procollagen extensions propeptide were measured by immunoassay (Synarc, Lyon, France). Statistical Analysis We used chi-square and t tests to compare baseline characteristics between case-patients with hip fracture and matched control participants. We assigned 25(OH) vitamin D concentrations to quartile categories defined on the basis of the distribution in the control participants. To further assess confounding, we compared baseline characteristics across quartiles of 25(OH) vitamin D concentrations in case-patients and control participants combined. We calculated the P values for trend by using logistic regression and coding the variable of interest as a continuous variable. We assessed the association between serum 25(OH) vitamin D concentrations and incident hip fracture in conditional logistic regression models that retained the matched casecontrol design. We first examined the unadjusted associations and then adjusted for age, b

Race and sex effects on the association between muscle strength, soft tissue, and bone mineral density in healthy elders : the health, aging, and body composition study

Two factors generally reported to influence bone density are body composition and muscle strength. However, it is unclear if these relationships are consistent across race and sex, especially in older persons. If differences do exist by race and/or sex, then strategies to maintain bone mass or minimize bone loss in older adults may need to be modified accordingly. Therefore, we examined the independent effects of bone mineral‐free lean mass (LM), fat mass (FM), and muscle strength on regional and whole body bone mineral density (BMD) in a cohort of 2619 well‐functioning older adults participating in the Health, Aging, and Body Composition (Health ABC) Study with complete measures. Participants included 738 white women, 599 black women, 827 white men, and 455 black men aged 70‐79 years. BMD (g/cm2) of the femoral neck, whole body, upper and lower limb, and whole body and upper limb bone mineral‐free LM and FM was assessed by dual‐energy X‐ray absorptiometry (DXA). Handgrip strength and knee extensor torque were determined by dynamometry. In analyses stratified by race and sex and adjusted for a number of confounders, LM was a significant (p < 0.001) determinant of BMD, except in white women for the lower limb and whole body. In women, FM also was an independent contributor to BMD at the femoral neck, and both FM and muscle strength contributed to limb BMD. The following were the respective β‐weights (regression coefficients for standardized data, Std β) and percent difference in BMD per unit (7.5 kg) LM: femoral neck, 0.202‐0.386 and 4.7‐5.9%; lower limb, 0.209‐0.357 and 2.9‐3.5%; whole body, 0.239‐0.484 and 3.0‐4.7%; and upper limb (unit = 0.5 kg), 0.231‐0.407 and 3.1‐3.4%. Adjusting for bone size (bone mineral apparent density [BMAD]) or body size BMD/height) diminished the importance of LM, and the contributory effect of FM became more pronounced. These results indicate that LM and FM were associated with bone mineral depending on the bone site and bone index used. Where differences did occur, they were primarily by sex not race. To preserve BMD, maintaining or increasing LM in the elderly would appear to be an appropriate strategy, regardless of race or sex.

Inflammatory markers and incident fracture risk in older men and women: the Health Aging and Body Composition Study.

The inflammation of aging hypothesis purports that aging is the accumulation of damage, which results, in part, from chronic activation of inflammation process. We tested this hypothesis in relationship to fractures in 2985 men and women enrolled in the Health ABC study. Results showed that subjects with the greatest number of inflammatory markers have the highest risk of fracture.

Serum 25-hydroxyvitamin D and clinical fracture risk in a multiethnic cohort of women: The women's health initiative (WHI)

Low 25‐hydroxyvitamin D [25(OH)D] levels have been linked to hip fracture in white women. To study the association of 25(OH)D with risk of fracture in multiethnic women, we performed a nested case‐control study within the prospective Womens Health Initiative (WHI) Observational Study. Incident fractures were identified in 381 black, 192 Hispanic, 113 Asian, and 46 Native American women over an average of 8.6 years. A random sample of 400 white women who fractured was chosen. One control individual was selected per case and matched on age, race/ethnicity, and blood draw date. 25(OH)D, parathyroid hormone, and vitamin D–binding protein (DBP) were measured in fasting baseline serum. Conditional logistic regression models were used to calculate the odds ratio (OR) and 95% CI. In multivariable models, higher 25(OH)D levels compared with levels less than 20 ng/mL were associated with a lower risk of fracture in white women (20 to <30 ng/mL: OR = 0.82, 95% CI 0.58–1.16; ≤30.0 ng/mL: OR = 0.56, 95% CI 0.35–0.90; p trend = 0.02). In contrast, higher 25(OH)D (≥20 ng/mL) compared with levels less than 20 ng/mL were associated with a higher risk of fracture in black women (OR = 1.45, 95% CI 1.06–1.98; p trend = 0.043). Higher 25(OH)D (≥30.0 ng/mL) was associated with higher fracture risk in Asian women after adjusting for DBP (OR = 2.78, 95% CI 0.99–7.80; p trend = 0.04). There was no association between 25(OH)D and fracture in Hispanic or Native American women. Our results suggest divergent associations between 25(OH)D and fracture by race/ethnicity. The optimal level of 25(OH)D for skeletal health may differ in white and black women.

Familial resemblance of bone mineral density (BMD) and calcaneal ultrasound attenuation : The BMD in Mothers and Daughters Study

The familial resemblance in bone mineral density (BMD) and calcaneal broadband ultrasound attenuation (BUA) was examined in 207 mother‐daughter pairs. Mothers were participants in the Study of Osteoporotic Fractures. Three groups of daughters were recruited based on their maternal history of “fracture,” “low BMD” without fracture (< 0.58 g/cm2, t‐score < −2.5), and “normal BMD” without fracture (> 0.67 g/cm2, t‐score > −1.6). Data on other potentially heritable factors known to influence BMD and BUA were also collected. BMD was measured at the hip, spine, whole body, and calcaneus. Calcaneal BUA was assessed using the Walker‐Sonix UBA 575. Total hip and femoral neck BMD were significantly lower (5.0–8.0%, p < 0.017) among daughters, in particular premenopausal daughters, of mothers with established osteoporosis (“fracture” or “low BMD”) compared with daughters of mothers at lower risk of osteoporosis (“normal BMD”). BUA did not differ across daughter groups. Lifestyle characteristics (dietary calcium, smoking, physical activity) were not highly correlated in mothers and daughters. Height, weight, and body composition were significantly correlated within mother‐daughter pairs and could be a potential mechanism by which BMD is inherited. Among pre‐ and postmenopausal daughters, heritability estimates ranged from 50–63% and 34–48%, respectively. Heritability for calcaneal BUA (53%) was evident among postmenopausal daughters only. In conclusion, familial association in BMD was strongest among premenopausal daughters. Estimates of heritability suggest that maternal BMD and BUA are important independent predictors of BMD and BUA among daughters, reinforcing the importance of prevention and early intervention among women with a positive family history of osteoporosis. (J Bone Miner Res 1999;14: 102–110)

Vitamin D Receptor Gene Polymorphisms, Bone Turnover, and Rates of Bone Loss in Older African-American Women†

Bone mineral density (BMD) is under genetic control. Some studies in Caucasian and Asian women suggest that polymorphisms in the vitamin D receptor (VDR) gene are associated with BMD and the rate of postmenopausal bone loss. We determined if similar associations exist in 101 African‐American women aged 65 years and older (71 ± 5 years, mean ± SD). We also examined the relation between VDR genotype and fractional45Ca absorption and markers of bone formation (osteocalcin) and resorption (N‐telopeptides) in these women. BMD was measured at the proximal femur and whole body at baseline and after 1.9 ± 0.4 years (femur only) on a Hologic QDR‐2000 densitometer using dual‐energy X‐ray absorptiometry. Calcaneal BMD was measured with single x‐ray absorptiometry. VDR gene polymorphisms were defined by the endonucleases BsmI, ApaI, and TaqI. These polymorphisms were not associated with BMD at any skeletal site or with markers of bone turnover. There was a significant interaction between age and VDR genotype where the oldest women (>70 years) with the tt genotype experienced greater hip bone loss than women with the TT genotype (−2.1%/year vs. −0.4%/year, respectively), whereas heterozygous women experienced an intermediate rate of bone loss (−1.3%/year). Women homozygous for the B allele had 14% lower fractional45Ca absorption compared with women homozygous for the b allele, although this difference was not statistically significant (p = 0.08). We conclude that VDR gene polymorphisms are not associated with BMD or indices of bone turnover in this population of older African‐American women. However, DNA sequence variation in the VDR gene or a nearby locus may influence intestinal calcium transport and the rate of postmenopausal bone loss in African‐American women.

Official Positions for FRAX ® Clinical Regarding International Differences. From Joint Official Positions Development Conference of the International Society for Clinical Densitometry and International Osteoporosis Foundation on FRAX ®

Osteoporosis is a serious worldwide epidemic. Increased risk of fractures is the hallmark of the disease and is associated with increased morbidity, mortality and economic burden. FRAX® is a web-based tool developed by the Sheffield WHO Collaborating Center team, that integrates clinical risk factors, femoral neck BMD, country specific mortality and fracture data and calculates the 10 year fracture probability in order to help health care professionals identify patients who need treatment. However, only 31 countries have a FRAX® calculator at the time paper was accepted for publication. In the absence of a FRAX® model for a particular country, it has been suggested to use a surrogate country for which the epidemiology of osteoporosis most closely approximates the index country. More specific recommendations for clinicians in these countries are not available. In North America, concerns have also been raised regarding the assumptions used to construct the US ethnic specific FRAX® calculators with respect to the correction factors applied to derive fracture probabilities in Blacks, Asians and Hispanics in comparison to Whites. In addition, questions were raised about calculating fracture risk in other ethnic groups e.g., Native Americans and First Canadians. In order to provide additional guidance to clinicians, a FRAX® International Task Force was formed to address specific questions raised by physicians in countries without FRAX® calculators and seeking to integrate FRAX® into their clinical practice. The main questions that the task force tried to answer were the following: The Task Force members conducted appropriate literature reviews and developed preliminary statements that were discussed and graded by a panel of experts at the ISCD-IOF joint conference. The statements approved by the panel of experts are discussed in the current paper.

Diabetes and Femoral Neck Strength: Findings from The Hip Strength Across the Menopausal Transition Study

CONTEXT Diabetes mellitus is associated with increased hip fracture risk, despite being associated with higher bone mineral density in the femoral neck. OBJECTIVE The objective of the study was to test the hypothesis that composite indices of femoral neck strength, which integrate dual-energy x-ray absorptiometry derived femoral neck size, femoral neck areal bone mineral density, and body size and are inversely associated with hip fracture risk, would be lower in diabetics than in nondiabetics and be inversely related to insulin resistance, the primary pathology in type 2 diabetes. DESIGN This was a cross-sectional analysis. SETTING AND PARTICIPANTS The study consisted of a multisite, multiethnic, community-dwelling sample of 1887 women in pre- or early perimenopause. OUTCOME MEASUREMENTS Composite indices for femoral neck strength in different failure modes (axial compression, bending, and impact) were measured. RESULTS Adjusted for age, race/ethnicity, menopausal stage, body mass index, smoking, physical activity, calcium and vitamin D supplementation, and study site, diabetic women had higher femoral neck areal bone mineral density [+0.25 sd, 95% confidence interval (CI) (+0.06, +0.44) sd] but lower composite strength indices [-0.20 sd, 95% CI (-0.38, -0.03) sd for compression, -0.19 sd, 95% CI (-0.38, -0.003) sd for bending, -0.19 sd, 95% CI (-0.37, -0.02) sd for impact] than nondiabetic women. There were graded inverse relationships between homeostasis model-assessed insulin resistance and all three strength indices, adjusted for the same covariates. CONCLUSIONS Despite having higher bone density, diabetic women have lower indices of femoral neck strength relative to load, consistent with their documented higher fracture risk. Insulin resistance appears to play an important role in bone strength reduction in diabetes.

Estrogen metabolites and the risk of breast cancer in older women.

Background Women who metabolize a large proportion of their estrogen via the 16&agr; hydroxylation pathway could be at a higher risk of breast cancer. The objective of this study was to test the hypothesis that serum concentrations of 2-hydroxyestrone (2-OHE1) and 16&agr;-hydroxyestrone (16&agr;-OHE1), as well as their ratio, predict the risk of breast cancer in older women. Methods We performed a case-cohort study of 272 women with confirmed incident breast cancer and 291 controls chosen randomly from the cohort. Estrogen metabolites were measured in serum collected at the baseline examination and stored at −120°C. Incident breast cancers were confirmed by medical records and pathology reports during an average follow-up of 8.7 years. Results Mean concentrations of 2-OHE1 and 16&agr;-OHE1, adjusted for age and body mass index, were 3% to 4% higher in cases compared with controls: 2-OHE1 was 176 pg/mL and 169 pg/mL and 16&agr;-OHE1 was 233 pg/mL and 226 pg/mL in cases and controls, respectively. There was, however, no difference in the ratio of 2-OHE1 to 16&agr;-OHE1. The risk of breast cancer in women with the highest quartile of this ratio compared with those in the lowest quartile was 1.17 (95% confidence interval = 0.73–1.87). Conclusion The study results do not support the hypothesis that the ratio of 2-OHE1 to 16&agr;-OHE1 predicts breast cancer risk.

Inflammatory markers and the risk of hip fracture: the Women's Health Initiative.

Cytokines play a major role in bone remodeling in vitro and in animal models, with evidence supporting the involvement of inflammatory markers in the pathogenesis of osteoporosis. However, less is known about the longitudinal association of inflammatory markers with hip fracture. We tested whether high receptor levels of proinflammatory cytokines are associated with an increased risk of hip fracture in older women. We used a nested case‐control study design from the Womens Health Initiative Observational Study (WHI‐OS) and selected 400 cases with physician‐adjudicated incident hip fractures and 400 controls matched on age, race, and date of blood draw. Participants were chosen from 39,795 postmenopausal women without previous hip fractures, not using estrogens or other bone‐active therapies. Incident hip fractures (median follow‐up 7.1 years) were verified by review of radiographs and confirmed by blinded central adjudicators. Hip fractures with a pathological cause were excluded. In multivariable models, the risk of hip fracture for subjects with the highest levels of inflammatory markers (quartile 4) compared with those with lower levels (quartiles 1, 2, and 3) was 1.43 (95% confidence interval [CI], 0.98–2.07) for interleukin‐6 (IL‐6) soluble receptor (SR), 1.40 (95% CI, 0.97–2.03) for tumor necrosis factor (TNF) SR1, and 1.56 (95% CI, 1.09–2.22) for TNF SR2. In subjects with all three markers in the highest quartile, the risk ratio of fracture was 2.76 (95% CI, 1.22–6.25) in comparison with subjects with 0 or 1 elevated marker(s) (p trend = 0.018). Elevated levels of inflammatory markers for all three cytokine‐soluble receptors were associated with an increased risk of hip fractures in older women. Future clinical trials should test whether interventions to decrease inflammatory marker levels reduces hip fractures.