Development and Evaluation of a Brief Calcium Assessment Tool for Adolescents

Associations Between Inflammatory Mediators and Bone Outcomes in Postmenopausal Women: A Cross-Sectional Analysis of Baseline Data from the Prune Study

Purpose

Hypoestrogenism triggers increased production of inflammatory mediators, which contribute to bone loss during postmenopausal osteoporosis. This study aimed to investigate the association between circulating inflammatory markers and bone outcomes in postmenopausal women.

Materials and methods

We conducted a cross-sectional, secondary analysis of baseline data from participants who completed a 12-month randomized controlled trial, The Prune Study (NCT02822378), which included healthy postmenopausal women (n=183, 55-75 years old) with bone mineral density (BMD) T-score between 0.0 and -3.0 at any site. BMD was measured using dual-energy X-ray absorptiometry, and bone geometry and strength were measured using peripheral quantitative computed tomography. Blood was collected at baseline to measure (1) serum biomarkers of bone turnover, including procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide and (2) inflammatory markers, including serum high-sensitivity C-reactive protein (hs-CRP) and plasma pro-inflammatory cytokines, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, and monocyte chemoattractant protein (MCP)-1, using enzyme-linked immunosorbent assay. The associations between bone and inflammatory outcomes at baseline were analyzed using correlation and regression analyses.

Results

Serum hs-CRP negatively correlated with P1NP (r=-0.197, p=0.042). Plasma IL-1β, IL-6, IL-8, and TNF-α negatively correlated with trabecular bone score at the lumbar spine (all p<0.05). In normal-weight women, plasma IL-1β, IL-6, and IL-8 negatively correlated (p<0.05) with trabecular and cortical bone area, content, and density at various sites in the tibia and radius. Serum hs-CRP positively predicted lumbar spine BMD (β=0.078, p=0.028). Plasma IL-6 negatively predicted BMD at the total body (β=-0.131, p=0.027) and lumbar spine (β=-0.151, p=0.036), whereas plasma TNF-α negatively predicted total hip BMD (β=-0.114, p=0.028).

Conclusion

At baseline, inflammatory markers were inversely associated with various estimates of bone density, geometry, and strength in postmenopausal women. These findings suggest that inflammatory markers may be an important mediator for postmenopausal bone loss.

Prunes preserve hip bone mineral density in a 12-month randomized controlled trial in postmenopausal women: the Prune Study

BACKGROUND

Dietary consumption of prunes has favorable impacts on bone health, but more research is necessary to improve upon study designs and refine our understandings.

OBJECTIVES

We evaluated the effects of prunes (50 g or 100 g/d) on bone mineral density (BMD) in postmenopausal women during a 12-mo dietary intervention. Secondary outcomes include effects on bone biomarkers.

METHODS

The single-center, parallel-arm 12-mo randomized controlled trial tested the effects of 50 g and 100 g prunes compared with a control group on BMD (every 6 mo) and bone biomarkers in postmenopausal women.

RESULTS

In total, 235 women (age 62.1 ± 5.0 y) were randomly allocated into control (n = 78), 50-g prune (n = 79), or 100-g prune (n = 78) groups. Compliance was 90.2 ± 1.8% and 87.1 ± 2.1% in the 50-g and 100-g prune groups. Dropout was 22%; however, the dropout rate was 41% for the 100-g prune group (compared with other groups: 10%, control; 15%, 50 g prune; P < 0.001). A group × time interaction for total hip BMD was observed in control compared with 50-g prune groups (P < 0.05) but not in control compared with 100-g prune groups (P > 0.05). Total hip BMD decreased -1.1 ± 0.2% in the control group at 12 mo, whereas the 50-g prune group preserved BMD (-0.3 ± 0.2%) at 12 mo (P < 0.05). Although hip fracture risk (FRAX) worsened in the control group at 6 mo compared with baseline (10.3 ± 0.5% compared with 9.8 ± 0.5%, P < 0.05), FRAX score was maintained in the pooled (50 g + 100 g) prune groups.

CONCLUSIONS

A 50-g daily dose of prunes can prevent loss of total hip BMD in postmenopausal women after 6 mo, which persisted for 12 mo. Given that there was high compliance and retention at the 50-g dosage over 12 mo, we propose that the 50-g dose represents a valuable nonpharmacologic treatment strategy that can be used to preserve hip BMD in postmenopausal women and possibly reduce hip fracture risk. This trial was registered at clinicaltrials.gov as NCT02822378.

Rationale and study design of Randomized Controlled Trial of Dietary Supplementation with prune (dried plums) on bone density, geometry, and estimated bone strength in postmenopausal women: The Prune study

The use of non-pharmacological alternatives to pharmacological interventions, e.g., nutritional therapy, to improve or maintain bone mineral density (BMD) in postmenopausal women has gained traction over the past decade, but limited data exist regarding its efficacy. This paper describes the design of the Prune Study, a randomized controlled trial (RCT) that explored the effectiveness of a 12-month intervention of daily prune consumption on bone density, bone structure and strength estimates, bone turnover, various biomarkers of immune function, inflammation, and cardiovascular health, as well as phenolic and gut microbiota analyses. Postmenopausal women between the ages of 55-75 years were randomized into either control group (no prune consumption; n = 78), 50g prune (50g prune/day; n = 79), or 100g prune (100g prune/day; n = 78). All participants received 1200 mg calcium +800 IU vitamin D3 daily as standard of care. The Prune Study is the largest and most comprehensive investigation of a dose response of prune consumption on bone health, biomarkers of immune function, inflammation, and cardiovascular health, as well as detailed phenolic and gut microbiota analyses in postmenopausal women. 235 women were randomized and 183 women completed the entire study. The findings of this study will help expand our current understanding of clinical implications and mechanisms underlying the resultant health effects of prune as a functional food therapy.

Low Energy Availability with and without a High-Protein Diet Suppresses Bone Formation and Increases Bone Resorption in Men: A Randomized Controlled Pilot Study

Suppression of insulin-like growth factor 1 (IGF-1) and leptin secondary to low energy availability (LEA) may contribute to adverse effects on bone health. Whether a high-protein diet attenuates these effects has not been tested. Seven men completed three five-day conditions operationally defined as LEA (15 kcal kg fat-free mass (FFM)⁻¹·day⁻¹) with low protein (LEA-LP; 0.8 g protein·kg body weight (BW)⁻¹), LEA with high protein (LEA-HP; 1.7 g protein·kg BW⁻¹) and control (CON; 40 kcal·kg FFM⁻¹·day⁻¹, 1.7 g protein·kg BW⁻¹). In all conditions, participants expended 15 kcal·kg FFM⁻¹·day⁻¹ during supervised cycling sessions. Serum samples were analyzed for markers of bone turnover, IGF-1 and leptin. The decrease in leptin during LEA-LP (−65.6 ± 4.3%) and LEA-HP (−54.3 ± 16.7%) was greater than during CON (−25.4 ± 11.4%; p = 0.02). Decreases in P1NP (p = 0.04) and increases in CTX-I (p = 0.04) were greater in LEA than in CON, suggesting that LEA shifted bone turnover in favour of bone resorption. No differences were found between LEA-LP and LEA-HP. Thus, five days of LEA disrupted bone turnover, but these changes were not attenuated by a high-protein diet.

Are the Effects of Oral and Vaginal Contraceptives on Bone Formation in Young Women Mediated via the Growth Hormone-IGF-I Axis?

Purpose: Combined hormonal contraceptive therapy has been associated with negative bone mineral density outcomes that may be route-dependent [i.e., combined oral contraception (COC) vs. contraceptive vaginal ring (CVR)] and involve the hepatic growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. The objective of the pilot study was to assess the impact of route of contraceptive administration on IGF-I and procollagen type I N-terminal propeptide (PINP) responses to an IGF-I Generation Test. We hypothesized that the peak rise in IGF-I and PINP concentration and area under the curve (AUC) would be attenuated following COC, but not CVR, use. Methods: Healthy, premenopausal women not taking hormonal contraception were recruited. Women were enrolled in the control group (n = 8) or randomly assigned to COC (n = 8) or CVR (n = 8) for two contraceptive cycles. IGF-I Generation Tests were used as a probe to stimulate IGF-I release and were completed during the pre-intervention and intervention phases. Serum IGF-I and PINP were measured during both IGF-I Generation Tests. The study was registered at ClinicalTrials.gov (NCT02367833). Results: Compared to the pre-intervention phase, peak IGF-I concentration in response to the IGF-I Generation Test in the intervention phase was suppressed in the COC group (p < 0.001), but not the CVR or Control groups (p > 0.090). Additionally, compared to the pre-intervention phase, PINP AUC during the intervention phase was suppressed in both COC and CVR groups (p < 0.001), while no difference was observed in the control group (p = 0.980). Conclusion: These data suggest that changes in recombinant human GH-stimulated hepatic IGF-I synthesis in response to combined hormonal contraception (CHC) use are dependent on route of CHC administration, while the influence on PINP is route-independent. Future research is needed to expand these results with larger randomized control trials in all age ranges of women who utilize hormonal contraception. Clinical Trial Registration: www.ClinicalTrials.gov registration NCT02367833.

Caloric restriction induces anabolic resistance to resistance exercise

Purpose

Weight loss can result in the loss of muscle mass and bone mineral density. Resistance exercise is commonly prescribed to attenuate these effects. However, the anabolic endocrine response to resistance exercise during caloric restriction has not been characterized.

Methods

Participants underwent 3-day conditions of caloric restriction (15 kcal kg FFM⁻¹) with post-exercise carbohydrate (CRC) and with post-exercise protein (CRP), and an energy balance control (40 kcal kg FFM⁻¹) with post-exercise carbohydrate (CON). Serial blood draws were taken following five sets of five repetitions of the barbell back squat exercise on day 3 of each condition.

Results

In CRC and CRP, respectively, growth hormone peaked at 2.6 ± 0.4 and 2.5 ± 0.9 times the peak concentrations observed during CON. Despite this, insulin-like growth factor-1 concentrations declined 18.3 ± 3.4% in CRC and 27.2 ± 3.8% in CRP, which was greater than the 7.6 ± 3.6% decline in CON, over the subsequent 24 h. Sclerostin increased over the first 2 days of each intervention by 19.2 ± 5.6% in CRC, 21.8 ± 6.2% in CRP and 13.4 ± 5.9% in CON, but following the resistance exercise bout, these increases were attenuated and no longer significant.

Conclusion

During caloric restriction, there is considerable endocrine anabolic resistance to a single bout of resistance exercise which persists in the presence of post-exercise whey protein supplementation. Alternative strategies to restore the sensitivity of insulin-like growth factor-1 to growth hormone need to be explored.

Electronic supplementary material

The online version of this article (10.1007/s00421-020-04354-0) contains supplementary material, which is available to authorized users.

Best Practices for Conducting Observational Research to Assess the Relation between Nutrition and Bone: An International Working Group Summary

Diet is a modifiable factor that can affect bone strength and integrity, and the risk of fractures. Currently, a hierarchy of scientific evidence contributes to our understanding of the role of diet on bone health and fracture risk. The strength of evidence is generally based on the type of study conducted, the quality of the methodology employed, the rigor and integrity of the data collected and analysis plan, and the transparency and completeness of the results. Randomized controlled trials (RCTs) are considered to be the gold standard from a clinical research paradigm, but there is a dearth of high-quality diet-related intervention trials with bone as the primary outcome, forcing the use of observational research to inform research and clinical practices. However, for observational research to be of the most utility, standardization and optimization of the study design, accurate and reliable measurement of key variables, and appropriate data analysis and data reporting are paramount. Although there have been recommendations made in relation to RCTs in the field of nutrition, no clear rubric exists for best practices in conducting observational research with regard to nutrition and bone health. Therefore, the purpose of this paper is to describe the best practices and considerations for designing, conducting, analyzing, interpreting, and reporting observational research specifically for understanding the role of nutrition in bone health, amassed by a global panel of scientific experts with strengths in bone, nutrition epidemiology, physical activity, public health, clinical and translational trials, and observational study methods. The global panel of scientific experts represents the leadership and selected participants from the 10th annual International Symposium for the Nutritional Aspects of Osteoporosis. The topics selected and best practices presented reflect expert opinion and areas of scientific expertise of the authors rather than a systematic or comprehensive literature review or professional reporting guidelines.

Adiposity, Insulin Resistance, and Bone Mass in Children and Adolescents

CONTEXT

Insulin resistance is an adverse health outcome that accompanies obesity. Fat mass is negatively associated with the bone mass after adjustment for confounders. Insulin resistance might be an intermediary in this relationship.

OBJECTIVE

To determine whether insulin resistance is an intermediary in the relationship between adiposity and bone mass in adolescents.

DESIGN

Cross-sectional secondary analysis of baseline data from a previous randomized trial.

SETTING

University research facility.

PARTICIPANTS

A total of 240 adolescents (68% female), aged 7 to 15 years.

MAIN OUTCOME MEASURES

Using dual energy x-ray absorptiometry, bone mineral content (BMC), areal bone mineral density, lean mass, and fat mass were measured. Skeletal sites of interest included the total body and lumbar spine (LS). Waist circumference was measured using an anthropometric tape measure. Insulin and glucose were measured in fasting sera, and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Path analysis was performed to determine whether the relationship between adiposity and bone was mediated through insulin resistance.

RESULTS

Fat mass (r = 0.467; P < 0.001) and waist circumference (r = 0.487; P < 0.001) correlated positively with HOMA-IR. Controlling for race, sex, maturation, lean mass, and height, fat mass, waist circumference, and HOMA-IR were negatively associated with LS BMC and total body areal bone mineral density (P < 0.05 for all). Additionally, path models for fat mass (95% CI, -5.893 to -0.956) and waist circumference (95% CI, -15.473 to -2.124) showed a negative relationship with LS BMC via HOMA-IR.

CONCLUSIONS

These results support an intermediary role of insulin resistance in the relationship between adiposity and LS bone mass.

Parent and household influences on calcium intake among early adolescents

BACKGROUND

Calcium intake during early adolescence falls short of requirements for maximum bone accretion. Parents and the home food environment potentially influence children's calcium intakes. This study aimed to quantify parental psychosocial factors (PSF) predicting calcium intakes of Asian, Hispanic, and non-Hispanic white (NHW) early adolescent children from a parental perspective.

METHODS

This was a cross-sectional study involving the administration of a validated calcium-specific food frequency questionnaire to a convenience sample of children aged 10-13 years and the primary individual responsible for food acquisition in the child's household. Based on Social Cognitive Theory, parental factors potentially associated with children's calcium intake were also assessed via parent questionnaires. The total study sample consisted of 633 parent-child pairs (Asian = 110, Hispanic = 239, NHW = 284). Questionnaires were completed at community-based centers/sites. Outcome measures were the association between parent-child calcium (mg), milk (cups/day), and soda (cans/day) intakes and the predictive value of significant parental PSF towards calcium intakes of their children. Sex-adjusted linear regression and multivariate analyses were performed.

RESULTS

Calcium intakes of parent-child pairs were positively associated among all ethnic groups (r = 0.296; P < 0.001). Soda intakes were positively associated among Hispanic parent-child pairs only (r = 0.343; P < 0.001). Home availability of calcium-rich foods (CRF), parental rules and expectations for their child's intake of beverages, and parents' calcium intake/role modeling were positively associated with children's calcium intake and overwhelmed all other PSF in multivariate analyses. Significant cultural differences were observed. Parental role modeling was a significant factor among Hispanic dyads only. Multivariate models explained 19-21% of the variance in children's calcium intakes.

CONCLUSIONS

Nutrition interventions to improve children's calcium intakes should focus on parents and provide guidance on improving home availability of CRF and increasing rules and expectations for the consumption of CRF. Among Hispanic families, interventions promoting parental modeling of desired dietary behaviors may be most successful.

The effect of dairy intake on bone mass and body composition in early pubertal girls and boys: a randomized controlled trial

Background: Calcium retention increases with increasing body mass index (BMI) on recommended calcium intakes. Dairy foods are an excellent source of essential nutrients that are needed to increase bone mineral content (BMC) and potentially decrease fracture.Objective: We compared children who were overweight with children who were healthy weight for the accrual of bone mass in response to an extra 3 servings dairy/d compared with usual intake.Design: Participants were 240 healthy boys and girls (64%), aged 8-15.9 y (mean ± SD age: 11.8 ± 1.5 y), who consumed low amounts of dairy (<800 mg Ca/d). A total of 181 subjects completed the trial-61% were black, 35% were white, and 4% were other; 50% of subjects were healthy weight [5th through 70th BMI percentiles for age (percentile)], and 50% of subjects were overweight (≥85th percentile). Participants were randomly assigned within BMI categories to receive an 18-mo dairy intervention (3 servings/d equivalent to ∼900 mg Ca/d) or control. Main outcome measures assessed every 6 mo included the total-body bone mineral content and density, cortical and trabecular bone mineral density (BMD), BMC, and bone area at the 4% tibia and anthropometric measures.Results: No significant differences in the change of BMD, BMC, or bone area for the total-body radius, lumbar spine, and total hip were observed between subjects who received the dairy intervention (achieved consumption of 1500 mg Ca/d) and subjects who did not (achieved 1000 mg Ca/d, which represented ∼2 cups milk or other dairy as part of the diet) with the exception of a tibial BMC gain, which was greater in the group who were given dairy (P = 0.02). Body fat was not influenced by the diet assignment.Conclusions: Dairy food interventions generally had no effect on bone mineral acquisition or body composition either within or between weight groups. This study suggests that 2 cups milk or the dairy equivalent is adequate for normal bone gain between ages 8 and 16 y. This trial was registered at clinicaltrials.gov as NCT00635583.

Evaluation of emotion-based messages designed to motivate Hispanic and Asian parents of early adolescents to engage in calcium-rich food and beverage parenting practices

BACKGROUND/OBJECTIVES

Setting healthful beverage expectations, making calcium-rich foods and beverages (CRF/B) available, and role modeling are parenting practices promoting calcium intake among early adolescents. This study aimed to evaluate emotion-based messages designed to motivate parents of early adolescents to perform these practices.

SUBJECTS/METHODS

Emotion-based messages were developed for each parenting practice and tested in 35 parents from 5 states. Findings were used to modify messages and develop a survey administered via Amazon MechanicalTurk to a convenience sample of Asian (n = 166) and Hispanic (n = 184) parents of children 10-13 years. Main outcome measures were message comprehension, motivation, relevance, acceptability, and novelty. Engagement in the parenting practices was also assessed.

RESULTS

Message comprehension was acceptable for the majority of parents. Most also agreed that messages were motivational (setting healthful beverage expectations (69.0%), making CRF/B available (67.4%), and role modeling (80.0%)), relevant and acceptable. About 30-50% indicated they had not seen the information before. Many parents indicated they were already engaging in the practices (> 70%). No racial/ethnic differences were observed for responses to messages or engaging in parenting practices.

CONCLUSIONS

Results indicate that emotion-based messages designed to motivate parents to engage in parenting practices that promote calcium intake among early adolescents were motivating, relevant, and acceptable.

Improving Milk Intake in Milk-Averse Lactose Digesters and Maldigesters

OBJECTIVE

To determine whether a 21-day milk-drinking intervention could reverse milk aversion.

DESIGN

Participants consumed increasing amounts of cow's milk for 21 days. Milk and dairy consumption, aversion, and likeness were assessed pre- and post-intervention and at 3 and 6 months post-intervention.

SETTING

A large Midwestern university.

PARTICIPANTS

Twenty-seven milk-averse individuals completed the intervention, 26 completed the 3-month follow-up, and 24 completed the 6-month follow-up.

MAIN OUTCOMES MEASURED

Participants self-reported milk and dairy consumption, aversion, and degree to which they liked milk.

ANALYSIS

Analysis of variance determined between-subject effects. Independent samples t test determined the effect of time. Fisher exact test determined factors affecting milk consumption.

RESULTS

Lactose digesters and maldigesters showed a significant decrease in overall symptom scores after the milk intervention, with no significant difference between groups. Independent of digestive status, subjects demonstrated a significant decrease in aversion, an increase in the amount to which they liked milk, and an increase in milk and overall calcium consumption at 3 and 6 months post-intervention.

CONCLUSIONS AND IMPLICATIONS

The results suggest a reversal of milk avoidance and the possibility that milk avoiders can increase likeness and incorporate milk into their diet after exposure.

Evaluation of tools used to measure calcium and/or dairy consumption in children and adolescents

OBJECTIVE

To identify and critique tools that assess Ca and/or dairy intake in children to ascertain the most accurate and reliable tools available.

DESIGN

A systematic review of the literature was conducted using defined inclusion and exclusion criteria. Articles were included on the basis that they reported on a tool measuring Ca and/or dairy intake in children in Western countries and reported on originally developed tools or tested the validity or reliability of existing tools. Defined criteria for reporting reliability and validity properties were applied.

SETTING

Studies in Western countries.

SUBJECTS

Children.

RESULTS

Eighteen papers reporting on two tools that assessed dairy intake, ten that assessed Ca intake and five that assessed both dairy and Ca were identified. An examination of tool testing revealed high reliance on lower-order tests such as correlation and failure to differentiate between statistical and clinically meaningful significance. Only half of the tools were tested for reliability and results indicated that only one Ca tool and one dairy tool were reliable. Validation studies showed acceptable levels of agreement (<100 mg difference) and/or sensitivity (62-83 %) and specificity (55-77 %) in three Ca tools. With reference to the testing methodology and results, no tools were considered both valid and reliable for the assessment of dairy intake and only one tool proved valid and reliable for the assessment of Ca intake.

CONCLUSIONS

These results clearly indicate the need for development and rigorous testing of tools to assess Ca and/or dairy intake in children and adolescents.

The association between serum 25-hydroxyvitamin d concentration and consumption frequencies of vitamin d food sources in korean adolescents

The objectives of this study were to investigate the status of vitamin D in Korean adolescents and to determine the association between serum 25-hydroxyvitamin D (25(OH)D) concentration and consumption frequencies of vitamin D food sources by season (June to November and December to May). The subjects were 1,579 adolescents aged 12-18 years participating in the 2008-2009 Korean National Health and Nutrition Examination Survey (KNHANES). Consumption frequencies of vitamin D food sources were estimated by using a qualitative food frequency questionnaire (FFQ). Thirteen food items were selected as vitamin D food sources including beef, egg, mackerel, tuna, yellow corvine, pollack, anchovy, mushroom, milk, yoghurt, ice cream, all fish and dairy products from the FFQ based on previous research. The data was analyzed using proc survey procedures. The deficiency (5.25-12 ng/mL), inadequacy (12-20 ng/mL) and sufficiency (> 20 ng/mL) proportions of serum 25(OH)D from June to November and December to May were 9.9%, 51.4%, 38.7%, and 39.4%, 51.4%, 9.2%, respectively. Mean serum 25(OH)D concentration was positively related to the consumption frequencies of mackerel, anchovy, all fish and milk. These results suggest high proportion (> 61%) of Korean adolescents were vitamin D deficiency or inadequacy, and serum 25(OH)D was associated with the consumption of vitamin D food sources including fish and milk.

Galacto-oligosaccharides increase calcium absorption and gut bifidobacteria in young girls: a double-blind cross-over trial

Adolescence is a time for rapid growth that represents an opportunity to influence peak bone mass. Prebiotic agents, such as galacto-oligosaccharides (GOS), increase Ca absorption in animal models and postmenopausal women. The objectives of the present study were to investigate the dose-response relationship of GOS supplementation on Ca absorption during growth and to assess changes in colonic microbiota to better understand the mechanism by which GOS is acting. A total of thirty-one healthy adolescent girls aged 10-13 years consumed smoothie drinks twice daily with 0, 2·5 or 5 g GOS for three 3-week periods in a random order. Fractional Ca absorption was determined from urinary Ca excretion over 48 h at the end of each 3-week period using a dual stable isotope method. Faecal microbiota and bifidobacteria were assessed by PCR-denaturing gradient gel electrophoresis and quantitative PCR. Fractional Ca absorption after the 48 h treatment with control, 5 and 10 g GOS/d was 0·393 (SD 0·092), 0·444 (SD 0·086) and 0·419 (SD 0·099), respectively. Significant improvements in Ca absorption were seen with both low and high doses of GOS compared with the control (P,0·02), but itwas not a dose-response relationship. The increase in absorption was greatest in the urine collected after 24 h, which is consistent with lower gut absorption. Faecal bifidobacteria increased (control 10·89 (SD 13·86), 5 g GOS 22·80 (SD 15·74) and 10 g GOS 11·54 (SD 14·20)) with the GOS treatment (P,0·03). The results suggest that daily consumption of 5 g GOS increases Ca absorption, which may be mediated by the gut microbiota, specifically bifidobacteria.

Body size and pubertal development explain ethnic differences in structural geometry at the femur in Asian, Hispanic, and white early adolescent girls living in the U.S

Variation in structural geometry is present in adulthood, but when this variation arises and what influences this variation prior to adulthood remains poorly understood. Ethnicity is commonly the focus of research of skeletal integrity and appears to explain some of the variation in quantification of bone tissue. However, why ethnicity explains variation in skeletal integrity is unclear.

METHODS

Here we examine predictors of bone cross sectional area (CSA) and section modulus (Z), measured using dual-energy X-ray absorptiometry (DXA) and the Advanced Hip Analysis (AHA) program at the narrow neck of the femur in adolescent (9-14 years) girls (n=479) living in the United States who were classified as Asian, Hispanic, or white if the subject was 75% of a given group based on parental reported ethnicity. Protocols for measuring height and weight follow standardized procedures. Total body lean mass (LM) and total body fat mass (FM) were quantified in kilograms using DXA. Total dietary and total dairy calcium intakes from the previous month were estimated by the use of an electronic semi-quantitative food frequency questionnaire (eFFQ). Physical activity was estimated for the previous year by a validated self-administered modifiable activity questionnaire for adolescents with energy expenditure calculated from the metabolic equivalent (MET) values from the Compendium of Physical Activities. Multiple regression models were developed to predict CSA and Z.

RESULTS

Age, time from menarche, total body lean mass (LM), total body fat mass (FM), height, total calcium, and total dairy calcium all shared a significant (p<0.05), positive relationship with CSA. Age, time from menarche, LM, FM, and height shared significant (p<0.05), positive relationships with Z. For both CSA and Z, LM was the most important covariate. Physical activity was not a significant predictor of geometry at the femoral neck (p≥0.339), even after removing LM as a covariate. After adjusting for covariates, ethnicity was not a significant predictor in regression models for CSA and Z.

CONCLUSION

Variability in bone geometry at the narrow neck of the femur is best explained by body size and pubertal maturation. After controlling for these covariates there were no differences in bone geometry between ethnic groups.