Racial differences in abdominal depot-specific adiposity in white and African American adults

Adipose tissue heterogeneity: implication of depot differences in adipose tissue for obesity complications

Obesity, defined as excess fat mass, increases risks for multiple metabolic diseases, such as type 2 diabetes, cardiovascular disease and several types of cancer. Over and above fat mass per se, the pattern of fat distribution, android or truncal as compared to gynoid or peripheral, has a profound influence on systemic metabolism and hence risk for metabolic diseases. Increases in upper body adipose tissue (visceral and abdominal subcutaneous) confer an independent risk, while the quantity of gluteofemoral adipose tissue is protective. Variations in the capacity of different depots to store and release fatty acids and to produce adipokines are important determinants of fat distribution and its metabolic consequences. Depot differences in cellular composition and physiology, including innervation and blood flow, likely influence their phenotypic properties. A number of lines of evidence also support the idea that adipocytes from different anatomical depots are intrinsically different as a result of genetic or developmental events. In this chapter, we will review the phenotypic characteristics of different adipose depots and mechanisms that link their depot-specific biology to metabolic complications in men and women.

Ethnic influences on the relations between abdominal subcutaneous and visceral adiposity, liver fat, and cardiometabolic risk profile: the International Study of Prediction of Intra-Abdominal Adiposity and Its Relationship With Cardiometabolic Risk/Intra-Abdominal Adiposity

BACKGROUND

Ethnic differences in cardiometabolic risk (CMR) may be related to patterns of ethnic-specific body fat distribution.

OBJECTIVE

We aimed to identify differences across ethnic groups in interrelations between BMI, abdominal adiposity, liver fat, and CMR profile.

DESIGN

In the International Study of Prediction of Intra-Abdominal Adiposity and Its Relationship With Cardiometabolic Risk/Intra-Abdominal Adiposity, 297 physicians recruited 4504 patients (from 29 countries). In the current cross-sectional analyses, 2011 whites, 166 African Caribbean blacks, 381 Hispanics, 1192 East Asians, and 347 Southeast Asians were included. Computed tomography was used to assess abdominal fat distribution and to estimate liver fat content. Anthropometric variables and CMR profile were measured.

RESULTS

Higher ranges of BMI were associated with higher levels of visceral [visceral adipose tissue (VAT)] and deep subcutaneous [deep subcutaneous adipose tissue (DSAT)] adiposity, with significant ethnic differences regarding the slope of these relations. Despite lower absolute BMI values, East Asians presented the largest accumulation of VAT but the lowest accumulation of DSAT with increasing adiposity. The association of BMI with liver fat did not differ between ethnic groups. Liver fat and DSAT were positively correlated with VAT with no ethnic variation. All ethnic groups had a similar association between a 1-SD increase in VAT, DSAT, or liver fat with hypertension, type 2 diabetes, hypertriglyceridemia, low HDL-cholesterol concentration, or high C-reactive protein concentration.

CONCLUSIONS

Ethnicity significantly affects abdominal adiposity and liver fat partitioning, and East Asians have the most deleterious abdominal fat distribution. Irrespective of ethnicity, abdominal and hepatic fat depots are strongly interrelated and increased with obesity. Higher amounts of VAT or liver fat are associated with a more deteriorated CMR profile in all ethnic groups.

Fatty liver, abdominal adipose tissue and atherosclerotic calcification in African Americans: the Jackson Heart Study

OBJECTIVE

Both fatty liver and abdominal visceral fat (VAT) are associated with cardiometabolic risk factors. Whether fatty liver and VAT are jointly associated with coronary artery (CAC) or abdominal aortic (AAC) calcification is not clear.

METHODS

Jackson Heart Study (JHS) participants (n = 2884, mean age 60 years, 65% women) underwent non-contrast CT Exam for assessment of fatty liver, VAT, and CAC and AAC. Fatty liver was measured by liver attenuation (LA; low LA = high fatty liver). The Agatston score was used to quantify the amount of calcified artery plaque and the presence of calcified artery plaque was defined as Agatston score>0. Cross-sectional associations of LA and VAT with CAC and AAC were examined in logistic regression models.

RESULTS

LA (per 1-standard deviation [SD] decrement) was associated inversely with CAC in age-sex-adjusted (OR 0.84, 95%CI 0.7-0.9, p = 0.0001) and multivariable-adjusted models (OR 0.89, 95%CI 0.8-0.9, p = 0.01). The association persisted for LA with CAC when additionally adjusted for body mass index (BMI) (OR 0.89, 95%CI 0.8-0.9, p = 0.03) or VAT (OR 0.90, 95%CI 0.8-0.9, p = 0.04). Abdominal VAT (per 1-SD increment) was positively associated with CAC in age-sex-adjusted models (OR 1.27, 95%CI 1.2-1.4, p = 0.0001), but the association was diminished with multivariable adjustment (OR 1.10, 95%CI 0.9-1.2, p = 0.09) and with additional adjustment for LA (p = 0.24) or BMI (p = 0.33). For AAC, the associations with LA and VAT were only present in age-sex-adjusted models. Finally, we did not observe interactions between LA and VAT for CAC (p = 0.18) or AAC (p = 0.24).

CONCLUSION

Fatty liver is associated with coronary atherosclerotic calcification independent of abdominal VAT or BMI in African Americans. Further investigations to uncover the clinical implications of fatty liver on coronary atherosclerosis in obesity are warranted.

Body mass index and the risk of dementia among Louisiana low income diabetic patients

Background

The association between obesity and dementia risk remains debatable and no studies have assessed this association among diabetic patients. The aim of our study was to investigate the association between body mass index (BMI) and dementia risk among middle and low income diabetic patients.

Methodology/Principal Findings

The sample included 44,660 diabetic patients (19,618 white and 25,042 African American) 30 to 96 years of age without a history of dementia in the Louisiana State University Hospital-Based Longitudinal Study. During a mean follow-up period of 3.9 years, 388 subjects developed incident dementia. The age- and sex-adjusted hazards ratios (HRs) for incident dementia at different levels of BMI (≤25, 25–26.9, 27–29.9, 30–34.9, and ≥35 kg/m²) were 1.00, 0.53 (95% CI 0.34–0.83), 0.29 (0.18–0.45), 0.37 (0.25–0.56), and 0.31 (0.21–0.48) (P_trend<0.001) in white diabetic patients, and 1.00, 1.00 (95% CI 0.62–1.63), 0.62 (0.39–0.98), 0.56 (0.36–0.86), and 0.65 (0.43–1.01) (P_trend = 0.029) in African American diabetic patients. Further adjustment for other confounding factors affected the results only slightly. There was a significant interaction between race and BMI on dementia risk (χ² = 5.52, 1df, p<0.025), such that the association was stronger in white patients. In stratified analyses, the multivariate-adjusted inverse association between BMI and risk of dementia was present in subjects aged 55–64 years, 65–74 years, and ≥75 years, in men and women, in non-smokers and smokers, and in subjects with different types of health insurance.

Conclusions/Significance

Higher baseline BMI was associated with a lower risk of dementia among diabetic patients, and this association was stronger among white than among African American diabetic patients.

Age at menarche and risk of type 2 diabetes among African-American and white women in the Atherosclerosis Risk in Communities (ARIC) study

AIMS/HYPOTHESIS

We examined race differences in the association between age at menarche and type 2 diabetes before and after adjustment for adiposity.

METHODS

We analysed baseline and 9-year follow-up data from 8,491 women (n = 2,505 African-American, mean age 53.3 years; n = 5,986 white, mean age 54.0 years) in the Atherosclerosis Risk in Communities (ARIC) study. Stratifying by race, we used logistic regression to estimate the OR for prevalent diabetes at baseline, and Cox proportional hazard models to estimate the HR for incident diabetes over follow-up according to age at menarche category (8-11, 12, 13, 14 and 15-18 years).

RESULTS

Adjusting for age and centre, we found that early age at menarche (8-11 vs 13 years) was associated with diabetes for white, but not African-American women in both the prevalent (white OR 1.72, 95% CI 1.32, 2.25; African-American OR 1.13, 95% CI 0.84, 1.51; interaction p = 0.043) and incident models (white HR 1.43, 95% CI 1.08, 1.89; African-American HR 1.20, 95% CI 0.87, 1.67; interaction p = 0.527). Adjustment for adiposity and lifestyle confounders attenuated associations for prevalent (white OR 1.41, 95% CI 1.05, 1.89; African-American OR 0.94, 95% CI 0.68, 1.30; interaction p = 0.093) and incident diabetes (white HR 1.22, 95% CI 0.92, 1.63; African-American HR 1.11, 95% CI 0.80, 1.56; interaction p = 0.554).

CONCLUSIONS/INTERPRETATION

Early menarche was associated with type 2 diabetes in white women, and adulthood adiposity attenuated the relationship. We did not find a similar association in African-American women. Our findings suggest that there may be race/ethnic differences in the influence of developmental factors in the aetiology of type 2 diabetes, which merit further investigation.

Abdominal obesity and mortality: The Pennington Center Longitudinal Study

The purpose of this study was to determine the association between visceral adipose tissue (VAT) and all-cause mortality. The sample included 1089 white men and women 18–84 years of age from the Pennington Center Longitudinal Study, a prospective cohort of participants assessed between 1995 and 2008, and followed for mortality until 31 December 2009. Abdominal VAT was measured at the L4–L5 vertebral level using computed tomography. There were 27 deaths during an average of 9.1 years of follow-up. Abdominal VAT was significantly associated with mortality after adjustment for age, sex and year of examination (hazards ratio (HR) 1.46; 95% confidence interval 1.05–2.05). The association was stronger after the inclusion of abdominal subcutaneous adipose tissue (SAT), smoking status, alcohol consumption and leisure-time physical activity as additional covariates (HR 1.74; 1.17–2.59). Limiting the sample to participants who were free of stroke, heart disease and cancer at baseline reduced the strength of the relationship slightly (HR 1.62; 1.07–2.47). Abdominal SAT was not associated with mortality, either alone or in combination with VAT and other covariates. The results support the assertion that abdominal VAT is an important therapeutic target for obesity reduction efforts.

Total and femoral neck bone mineral density and physical activity in a sample of men and women

Physical activity (PA), total body fat (TBF), and lean body mass (LBM) are associated with bone mineral density (BMD). However, the independent influence of PA on BMD, while controlling for body composition is not understood as well and is the purpose of the current study. Whole-body BMD (g·cm⁻²), femoral neck BMD (g·cm⁻²), TBF (kg), and LBM (kg) were measured with dual-energy X-ray absorptiometry. PA levels (total, work, sport, non-sport) were estimated using the Baecke questionnaire. General linear models determined the independent effects of PA on BMD (whole-body and femoral neck), with adjustment for age, sex, ethnicity, smoking, menopausal status (as appropriate), LBM, and TBF. These associations were also examined by sex and age group (20-34, 35-49, and 50-64 years). The sample included 802 adults (65% women; 13% African American) from the Pennington Center Longitudinal Study that were 20 to 64 years of age (mean ± SD: 46.9 ± 11.0 years). Higher sports scores were associated with higher femoral neck BMD in the total group, men and women, and in 20- to 34-year-olds and 35- to 49-year-olds, but not significant in those 50-64 years of age. Similar significant associations were found for sports score with total body BMD; however, this relationship was not significant for women or for those 50-64 years of age. Total PA had inconsistent relationships with both femoral neck BMD and total body BMD. Higher levels of sport-related PA are associated with higher femoral neck BMD; however, these relationships vary by PA domain and site of BMD measurement.

Intramyocellular lipid is associated with visceral adiposity, markers of insulin resistance, and cardiovascular risk in prepubertal children: the EPOCH study

CONTEXT

The intramyocellular deposition of lipid associates with metabolic dysregulation in adolescents and adults. Relatively little is known about the deposition of fat in muscle before the onset of puberty.

OBJECTIVE

Our objective was to describe the relationship between intramyocellular lipid (IMCL) accumulation and 1) visceral adiposity and 2) markers of insulin resistance and cardiovascular disease risk in a cohort of prepubertal and early pubertal children.

STUDY DESIGN

Data were collected as part of a retrospective cohort study, Exploring Perinatal Outcomes among Children (EPOCH). Multiple linear regression models were constructed for data analysis.

RESULTS

A total of 441 children participated in the study (226 prepubertal, 215 early pubertal). In prepubertal children, there was a significant relationship between IMCL and visceral fat (parameter estimate 0.019, P = 0.002) that remained after controlling for body mass index. Independent of overall adiposity, in all children, IMCL was associated with the triglyceride to high-density lipoprotein ratio (parameter estimate 0.1418, P = 0.002).

CONCLUSIONS

This study demonstrates a concerning and related pattern of IMCL and visceral fat deposition in prepubertal children. Intramuscular fat deposition is linked to markers of insulin resistance and cardiovascular disease risk.

Best single-slice measurement site for estimating visceral adipose tissue volume after weight loss in obese, Japanese men

BACKGROUND

Although the measurement site at L4-L5 for visceral adipose tissue (VAT) has been commonly accepted, some researchers suggest that additional upper sites (i.e., L1-L2 and L2-L3) are useful for estimating VAT volume. Therefore, determining the optimum measurement site remains challenging and has become important in determining VAT volume. We investigated the influence of a single-slice measurement site on the prediction of VAT volume and changes in VAT volume in obese Japanese men.

METHODS

Twenty-four men, aged 30-65 years with a mean BMI of 30 kg/m2, were included in a 12-week weight loss program. We obtained continuous T1-weighted abdominal magnetic resonance images from T9 to S1 with a 1.5-T system to measure the VAT area. These VAT areas were then summed to determine VAT volume before and after the program.

RESULTS

Single-slice images at 3-11 cm above L4-L5 had significant and high correlations with VAT volume at baseline (r=0.94-0.97). The single-slice image with the highest correlation coefficient with respect to VAT volume was located at 5 cm above L4-L5 (r=0.97). The highest correlation coefficient between the individual changes in VAT area and changes in VAT volume was located at 6 cm above L4-L5 (r=0.90).

CONCLUSIONS

Individual measurement sites have different abilities to estimate VAT volume and changes in VAT volume in obese Japanese men. Best zone located at 5-6 cm above L4-L5 may be a better predictor of VAT volume than the L4-L5 image in terms of both baseline and changes with weight loss.

Ethnic differences in glucose disposal, hepatic insulin sensitivity, and endogenous glucose production among African American and European American women

Intravenous glucose tolerance tests have demonstrated lower whole-body insulin sensitivity (S(I)) among African Americans (AA) compared with European Americans (EA). Whole-body S(I) represents both insulin-stimulated glucose disposal, primarily by skeletal muscle, and insulin's suppression of endogenous glucose production (EGP) by liver. A mathematical model was recently introduced that allows for distinction between disposal and hepatic S(I). The purpose of this study was to examine specific indexes of S(I) among AA and EA women to determine whether lower whole-body S(I) in AA may be attributed to insulin action at muscle, liver, or both. Participants were 53 nondiabetic, premenopausal AA and EA women. Profiles of EGP and indexes of Disposal S(I) and Hepatic S(I) were calculated by mathematical modeling and incorporation of a stable isotope tracer ([6,6-(2)H(2)]glucose) into the intravenous glucose tolerance test. Body composition was assessed by dual-energy x-ray absorptiometry. After adjustment for percentage fat, both Disposal S(I) and Hepatic S(I) were lower among AA (P = .009 for both). Time profiles for serum insulin and EGP revealed higher peak insulin response and corresponding lower EGP among AA women compared with EA. Indexes from a recently introduced mathematical model suggest that lower whole-body S(I) among nondiabetic AA women is due to both hepatic and peripheral components. Despite lower Hepatic S(I), AA displayed lower EGP, resulting from higher postchallenge insulin levels. Future research is needed to determine the physiological basis of lower insulin sensitivity among AA and its implications for type 2 diabetes mellitus risk.

Anthropometric correlates of total body fat, abdominal adiposity, and cardiovascular disease risk factors in a biracial sample of men and women

OBJECTIVE

To investigate associations between anthropometric measurements and total body fat, abdominal adipose tissue, and cardiovascular disease risk factors in a large biracial sample.

PATIENTS AND METHODS

This study is limited to cross-sectional analyses of data from participants attending a baseline visit between January 26, 1996, and February 1, 2011. The sample included 2037 individuals aged 18 to 69 years: 488 African American women (24%), 686 white women (34%), 196 African American men (9%), and 667 white men (33%). Anthropometry included weight; hip circumference; waist circumference; waist-hip, waist-height, and weight-height ratios; body adiposity index; and body mass index. Body fat and percentage of fat were measured by dual-energy x-ray absorptiometry, and abdominal visceral and subcutaneous adipose tissue were measured by computed tomography. Bivariate correlations, logistic regression models, and receiver operator characteristic curves were used, and analyses were stratified by sex and race.

RESULTS

In each sex-by-race group, all anthropometric measures were highly correlated with percentage of fat, fat mass, and subcutaneous adipose tissue and moderately correlated with visceral adipose tissue, with the exception of the waist-hip ratio. The odds of having an elevated cardiometabolic risk were increased more than 2-fold per SD increase for most anthropometric variables, and the areas under the curve for each anthropometric measure were significantly greater than 0.5.

CONCLUSION

Several common anthropometric measures were moderately to highly correlated with total body fat, abdominal fat, and cardiovascular disease risk factors in a biracial sample of women and men. This comprehensive analysis provides evidence of the linkage between simple anthropometric measurements and the purported pathways between adiposity and health.

Markers of inflammation and fat distribution following weight loss in African-American and white women

Changes in markers of inflammation (MOI) and fat distribution with weight loss between African-American (AA) and white (W) women have yet to be characterized. The purpose of this study was to examine potential ethnic differences in MOI and regional fat distribution with weight loss, and identify the associations between these markers and changes in regional fat distribution with weight loss among AA and W women. Subjects were 126 healthy, premenopausal women, BMI 27-30 kg/m(2). They were placed on a weight-loss intervention consisting of diet and/or exercise until a BMI <25 was achieved. Fat distribution was measured with computed tomography, and body composition with dual-energy X-ray absorptiometry. Serum concentrations of tumor necrosis factor-α (TNF-α), soluble TNF receptor-I (sTNFR-I), sTNFR-II, C-reactive protein (CRP), and interleukin-6 (IL-6) were assessed. All MOI and adiposity measures significantly decreased with weight loss. Significant ethnic differences with weight loss were observed for fat mass, body fat, intra-abdominal adipose tissue (IAAT), sTNFR-I, and sTNFR-II. Mixed-model analysis indicated that adjusting for change in IAAT explained ethnic differences in change in TNF-α and the decrease in TNF-α with weight loss, while total fat mass only explained the decrease in sTNFR-I and sTNFR-II with weight loss. In conclusion, all MOI decreased following weight loss among W, whereas only IL-6 and CRP decreased following weight loss in AA. The most distinct phenotypic difference observed was a greater impact of weight loss on TNF-α in W compared to AA, which was directly associated with IAAT in W.

Body fat distribution and breast cancer risk: findings from the Nigerian breast cancer study

PURPOSE

The relationship between overall obesity and breast cancer risk has been well recognized, but the role of central obesity in breast cancer development is uncertain.

METHODS

Between 1998 and 2009, 1,233 invasive breast cancer cases and 1,101 community controls were recruited into the Nigerian Breast Cancer Study at Ibadan, Nigeria. Logistic regressions were used to calculate multivariate odds ratio (OR) and 95% confidence intervals (CI), adjusting for age, body mass index (BMI), and other known risk factors for breast cancer.

RESULTS

The OR for the highest quartile group of waist circumference relative to the lowest was 2.39 (95% CI, 1.59-3.60; P-trend < 0.001). Comparing women with waist/hip ratio (WHR) in the lowest quartile group, the OR for women in the highest quartile category was 2.15 (95% CI, 1.61-2.85; P-trend < 0.001). An inverse association was observed between hip circumference and breast cancer, with an OR of 0.36 for the highest quartile (95% CI, 0.24-0.55; P-trend < 0.001). The effects of these three measures existed in both pre- and postmenopausal women. Of note, we found a significant interaction between WHR and BMI (P-interaction = 0.016): the OR comparing the highest to the lowest WHR quartile was 2.81 (95% CI, 1.90-4.16) for women with BMI < 25 kg/m2 and 1.70 (95% CI, 1.11-2.61) for women with BMI ≥ 25 kg/m2.

CONCLUSIONS

These results suggest that central adiposity, measured by waist circumference and waist/hip ratio, was an important risk factor for breast cancer in Nigerian women, and the effect of central adiposity was strong in normal-weight women.

Lifestyle factors and 5-year abdominal fat accumulation in a minority cohort: the IRAS Family Study

The objective of this study was to examine whether lifestyle factors were associated with 5-year change in abdominal fat measured by computed tomography (CT) in the Insulin Resistance and Atherosclerosis (IRAS) Family Study. We obtained abdominal CT scans at baseline and at 5 years, from African Americans (AA) (N = 339) and Hispanic Americans (N = 775), aged 18-81 years. Visceral (VAT) and subcutaneous (SAT) adipose tissue was measured at the L4/L5 vertebral level. Physical activity was documented by self-report of vigorous activity and a 1-year recall instrument. Dietary intake was assessed at follow-up using a semi-quantitative food frequency questionnaire referencing the previous year. Generalized linear models, accounting for family structure, were used to assess the associations between percent change in fat accumulation and smoking, physical activity, total calories, polyunsaturated, monounsaturated, protein, and saturated fat intake, percent of calories from sweets, and soluble and insoluble fiber. Soluble fiber intake and participation in vigorous activity were inversely related to change in VAT, independent of change in BMI. For each 10 g increase in soluble fiber, rate of VAT accumulation decreased by 3.7% (P = 0.01). Soluble fiber was not associated with change in SAT (0.2%, P = 0.82). Moderately active participants had a 7.4% decrease in rate of VAT accumulation and a 3.6% decrease in rate of SAT accumulation versus less active participants (P = 0.003 and P = 0.01, respectively). Total energy expenditure was also inversely associated with accumulation of VAT. Soluble fiber intake and increased physical activity were related to decreased VAT accumulation over 5 years.

Relationship between abdominal fat and bone mineral density in white and African American adults

Several studies have documented relationships between adipose tissue and bone mineral density (BMD); however, the degree to which there are racial differences in this relationship is not known. The purpose of this study was to examine the relationships between abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) and BMD among white and African American adults. The sample included 330 white women, 328 African American women, 307 white men, and 116 African American men 18-74 years of age. Dual-energy X-ray absorptiometry scans were used to measure BMD and computed tomography scans were used to measure abdominal VAT and SAT. Linear regression was used to assess the relationships between abdominal adiposity and BMD and to explore possible sex and race differences in the associations. In the total sample as well as in all sex-by-race groups, VAT and SAT were negatively related to BMD, after adjustment for lean body mass (LBM) and several covariates. The VAT model (including covariates) explained 33.3% of the variance in BMD and the SAT model (including covariates) explained 32.7% of the variance in BMD. Being African American, being male, and having high LBM were all associated with higher BMD. Race and sex interactions were not significant, indicating that the relationships were similar across race and sex groups. In conclusion, BMD was inversely related to abdominal VAT and SAT in white and African American adults after adjustment for LBM.

The Association between Self-Reported Energy Intake and Intra-Abdominal Adipose Tissue in Perimenopausal Women

We have previously shown that physical activity predicts intra-abdominal adipose tissue (IAT), but it is unknown whether energy intake predicts IAT independently of physical activity in a community-based, naturalistic environment. The association of energy intake with IAT was explored cross-sectionally in women, recruited between 2002 and 2005 for a study of fat patterning in midlife. IAT at L(4)-L(5) vertebral interspace was assessed by computed tomography, energy intake by the Block Food Frequency Questionnaire, and physical activity by the Kaiser Physical Activity Survey. Linear regression models were used for the principal analyses. Among the 257 women, 48% were African American and 52% were Caucasian. Women were 52 ± 3 years old, and 49% were postmenopausal. Every 500 kcal increase in energy intake was associated with a 6% higher IAT (P = 0.02), independent of physical activity (P = 0.02), after adjustment for ethnicity, menopausal status, age, smoking, income, and DXA-assessed percent body fat. Energy intake had a significant interaction with ethnicity (P = 0.02), but not with physical activity. Models using the IAT to subcutaneous abdominal adipose tissue ratio as an outcome had similar associations. In conclusion, self-reported EI was associated with preferential IAT accumulation in midlife women, independent of physical activity. This association was significantly stronger in Caucasian than African American women. Future longitudinal studies are needed to explore lifestyle predictors of IAT accumulation during the menopausal transition.

Fatty liver, abdominal visceral fat, and cardiometabolic risk factors: the Jackson Heart Study

OBJECTIVE

The goal of this study was to examine whether fatty liver and abdominal visceral adipose tissue (VAT) are jointly associated with cardiometabolic abnormalities.

METHODS AND RESULTS

Black participants were from the Jackson Heart Study (n=2882, 65% women) who underwent computed tomography. Fatty liver was measured by liver attenuation in Hounsfield units (LA), and VAT was quantified volumetrically. Cross-sectional associations between LA, VAT, and cardiometabolic risk factors were assessed using linear and logistic regression, and their joint associations were further examined in 4 subgroups: high-LA/low-VAT (n=1704), low-LA/low-VAT (n=422), high-LA/high-VAT (n=436), and low-LA/high-VAT (n=320). Both LA and VAT were associated with most cardiometabolic traits (all P<0.0001), which persisted after additional adjustment for each other (LA, P<0.01-0.0001; VAT, P<0.0001). In bootstrap analyses, the regression coefficient of VAT was significantly greater than LA for triglycerides, high-density lipoprotein cholesterol, impaired glucose, and metabolic syndrome (P=0.009-0.0001). The interaction between LA and VAT was significant for high-density lipoprotein cholesterol (P=0.002), impaired glucose (P=0.003), and metabolic syndrome (P=0.04). Among 4 subgroups, participants with higher VAT and lower LA had higher prevalence of cardiometabolic traits than those with each condition alone.

CONCLUSION

Both fatty liver and VAT are independent correlates of cardiometabolic risk, but the associations are stronger for VAT than for fatty liver.

Ratio of visceral to subcutaneous fat area is a biomarker of complicated Crohn's disease

BACKGROUND & AIMS

Fat wrapping and mesenteric hypertrophy are characteristics of Crohn's disease (CD). In patients with CD, mesenteric adipose tissue releases higher levels of adiponectin, which could up-regulate production of tumor necrosis factor-α and increase the risk for aggressive disease. We investigated whether a higher ratio of visceral to subcutaneous fat was associated with complicated (fistulating or stricturing) CD.

METHODS

We identified patients with a confirmed diagnosis of CD who had computed tomography scans of their abdomens (n = 50). Areas of subcutaneous and visceral fat were measured in 1 cross-sectional scan that was taken at the level of the umbilicus. The mesenteric fat index (MFI), defined as the ratio of areas of visceral to subcutaneous fat, was compared between patients with complicated (strictures and fistulas) and inflammatory CD.

RESULTS

The mean age of the patients with complications (n = 29) was 49.3 ± 15.6 years, and in patients with inflammatory CD (n = 21) it was 37.7 ± 19.1 years. The MFI was significantly higher (P = .001) in patients with complicated disease (0.67 ± 0.29) than in those with uncomplicated disease (0.23 ± 0.10) and was the only variable that remained significantly different on multivariate analysis. The area under the receiver operating curve for the MFI was 0.95 (95% confidence interval, 0.89-1.0), and an MFI of 0.29 identified patients with complicated CD with 93% sensitivity and 81% specificity.

CONCLUSIONS

A high ratio of areas of visceral to subcutaneous fat (MFI) is a marker of aggressive CD. Further studies are needed to determine the roles of adipose tissue in pathogenesis of CD.

Adiposity attenuates muscle quality and the adaptive response to resistance exercise in non-obese, healthy adults

BACKGROUND

Emerging data have revealed a negative association between adiposity and muscle quality (MQ). There is a lack of research to examine this interaction among young, healthy individuals, and to evaluate the contribution of adiposity to adaptation after resistance exercise (RE).

OBJECTIVE

The purpose of this investigation was to examine the influence of subcutaneous adipose tissue (SAT) on muscle function among non-obese individuals before and after RE.

DESIGN

Analyses included 634 non-obese (body mass index <30 kg m(-2)) subjects (253 males, 381 females; age=23.3 ± 5.2 years). SAT and muscle mass (magnetic resonance imaging-derived SAT and biceps muscle volume), isometric and dynamic biceps strength, and MQ (strength/muscle volume), were analyzed at baseline and after 12 weeks of unilateral RE.

RESULTS

At baseline, SAT was independently associated with lower MQ for males (β=-0.55; P<0.01) and females (β=-0.45; P<0.01), controlling for body mass and age. Adaptation to RE revealed a significant negative association between SAT and changes for strength capacity (β=-0.13; p=0.03) and MQ (β=-0.14; P<0.01) among males. No attenuation was identified among females. Post-intervention SAT remained a negative predictor of MQ for males and females (β=-0.47; P<0.01).

CONCLUSIONS

The findings reveal that SAT is a negative predictor of MQ among non-obese, healthy adults, and that after 12 weeks of progressive RE this association was not ameliorated. Data suggest that SAT exerts a weak, negative influence on the adaptive response to strength and MQ among males.

Invited commentary: Discrimination--an emerging target for reducing risk of cardiovascular disease?

A growing body of research suggests that perceived discrimination, in multiple societies, is a neglected but important predictor of increased risk of disease for a broad range of health status indicators. Several prior studies propose that discrimination is adversely related to increased cardiovascular disease risk. The studies by Hunte (Am J Epidemiol. 2011;173(11):1223-1231) and Lewis et al. (Am J Epidemiol. 2011;173(11):1232-1239) find that self-reported discrimination is associated with increased risk of adiposity for men and women. These studies highlight the potentially important role of discrimination as a risk factor for excess fat but also raise important research questions regarding the role of fat in cardiovascular disease and racial differences in these processes. More generally, they also provide an important reminder to epidemiologists and medical professionals that discrimination and other aspects of racism persist in contemporary society and that increased efforts are needed to document the extent to which they may have pathogenic consequences and to identify the most promising initiatives to reduce any observed negative effects. Equally important, these studies remind us that, although social stressors are difficult to measure accurately and comprehensively, understanding how multiple stressors combine over the life course to affect the risk of morbidity and mortality remains an important priority for concerted research attention.

Trunk versus extremity adiposity and cardiometabolic risk factors in white and African American adults

OBJECTIVE

To determine contributions of trunk and extremity adiposity to cardiometabolic risk factors (blood pressure, fasting blood glucose, HDL cholesterol, and triglycerides) among white and African American adults.

RESEARCH DESIGN AND METHODS

The sample consisted of 1,129 white women, 779 African American women, 1,012 white men, and 300 African American men.

RESULTS

Higher trunk adiposity was significantly associated with an increased risk of having two or more cardiometabolic risk factors among African American and white men and women. After adjustment for trunk and arm adiposity, higher leg adiposity was significantly associated with a decreased risk of having two or more cardiometabolic risk factors among white men and women and African American women.

CONCLUSIONS

In contrast with adverse risk with high trunk adiposity, high leg adiposity is associated with a decreased risk of having two or more cardiometabolic risk factors in both African American and white adults.

Body composition phenotypes in pathways to obesity and the metabolic syndrome

Dynamic changes in body weight have long been recognized as important indicators of risk for debilitating diseases. While weight loss or impaired growth can lead to muscle wastage, as well as to susceptibility to infections and organ dysfunctions, the development of excess fat predisposes to type 2 diabetes and cardiovascular diseases, with insulin resistance as a central feature of the disease entities of the metabolic syndrome. Although widely used as the phenotypic expression of adiposity in population and gene-search studies, body mass index (BMI), that is, weight/height(2) (H(2)), which was developed as an operational definition for classifying both obesity and malnutrition, has considerable limitations in delineating fat mass (FM) from fat-free mass (FFM), in particular at the individual level. After an examination of these limitations within the constraints of the BMI-FM% relationship, this paper reviews recent advances in concepts about health risks related to body composition phenotypes, which center upon (i) the partitioning of BMI into an FM index (FM/H(2)) and an FFM index (FFM/H(2)), (ii) the partitioning of FFM into organ mass and skeletal muscle mass, (iii) the anatomical partitioning of FM into hazardous fat and protective fat and (iv) the interplay between adipose tissue expandability and ectopic fat deposition within or around organs/tissues that constitute the lean body mass. These concepts about body composition phenotypes and health risks are reviewed in the light of race/ethnic variability in metabolic susceptibility to obesity and the metabolic syndrome.

Waist circumference, BMI, and visceral adipose tissue in white women and women of African descent

Although waist circumference (WC) is a marker of visceral adipose tissue (VAT), WC cut-points are based on BMI category. We compared WC-BMI and WC-VAT relationships in blacks and whites. Combining data from five studies, BMI and WC were measured in 1,409 premenopausal women (148 white South Africans, 607 African-Americans, 186 black South Africans, 445 West Africans, 23 black Africans living in United States). In three of five studies, participants had VAT measured by computerized tomography (n = 456). Compared to whites, blacks had higher BMI (29.6 ± 7.6 (mean ± s.d.) vs. 27.6 ± 6.6 kg/m², P = 0.001), similar WC (92 ± 16 vs. 90 ± 15 cm, P = 0.27) and lower VAT (64 ± 42 vs. 101 ± 59 cm², P < 0.001). The WC-BMI relationship did not differ by race (blacks: β (s.e.) WC = 0.42 (.01), whites: β (s.e.) WC = 0.40 (0.01), P = 0.73). The WC-VAT relationship was different in blacks and whites (blacks: β (s.e.) WC = 1.38 (0.11), whites: β (s.e.) WC = 3.18 (0.21), P < 0.001). Whites had a greater increase in VAT per unit increase in WC. WC-BMI and WC-VAT relationships did not differ among black populations. As WC-BMI relationship did not differ by race, the same BMI-based WC guidelines may be appropriate for black and white women. However, if WC is defined by VAT, race-specific WC thresholds are required.

The relationship of waist circumference and BMI to visceral, subcutaneous, and total body fat: sex and race differences

The purpose of this study was to examine sex and race differences in the relationship between anthropometric measurements and adiposity in white and African-American (AA) adults. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas were measured with computed tomography (CT). Fat mass (FM) was measured with dual-energy-X-ray absorptiometry (DXA). Correlation coefficients were used to assess the relationship of waist circumference (WC) and BMI to VAT, SAT, and FM within sex-by-race groups. General linear models were used to compare relationships between WC or BMI, and adiposity across sex and race, within age groups (18-39 and 40-64 years). The sample included 1,667 adults (men: 489 white; 120 AA; women: 666 white, 392 AA). WC and BMI correlations were highest for FM and SAT compared to VAT. Women had higher FM levels than men regardless of WC, but the sex difference in FM was attenuated in younger AA adults with a high BMI. For a given level of WC or BMI, women had higher levels of SAT than men; however, significant interactions indicated that the relationship was not consistent across all levels of BMI and WC. Sex and race differences in VAT varied significantly with WC and BMI. In general, white adults had higher levels of VAT than AA adults at higher levels of BMI and WC. Sex differences, and in some instances race differences, in the relationships between anthropometry and fat-specific depots demonstrate that these characteristics need to be considered when predicting adiposity from WC or BMI.

Pediatric obesity epidemiology

PURPOSE OF REVIEW

To provide updated summary of recently published data regarding pediatric obesity epidemiology.

RECENT FINDINGS

There is a burgeoning literature of pediatric obesity epidemiology, with type 2 diabetes trends serving as the harbinger for obesity related diseases in children. The National Health and Nutrition Examination Survey and Pediatric Nutrition Surveillance System report a tripling of the prevalence of BMI at least 95% (obesity) among US school-age children and adolescents over the past three decades. Recent updates provide insight into infants and toddler obesity and explore the impact of ethnicity, socioeconomic status, school setting and geographic variations. International data confirm similar upward shifts in pediatric BMI distribution, especially in countries undergoing economic transitions favoring industrialized, western urban lifestyles.

SUMMARY

The health and financial consequences of this epidemic are a complex global public health dilemma. International efforts are underway to reverse these obesity trends. On-going analysis of obesity prevalence and exploration of potential causal associations are required to implement and assess the effectiveness of interventions and policies.

Are adult body circumferences associated with height? Relevance to normative ranges and circumferential indexes

BACKGROUND

Weight scales as height squared, which is an observation that forms the basis of body mass index (weight/height(2)). If, and how, circumferences, including waist circumference (WC) and hip circumference (HC), scale to height remains unclear, but this is an important consideration when developing normative ranges or applying WC/height and HC/height as risk indexes.

OBJECTIVE

The study aim was to examine the scaling of weight, WC, and HC to height in NHANES (National Health and Nutrition Examination Survey) III participants.

DESIGN

Subjects were adult non-Hispanic white, non-Hispanic black, and Mexican American men (n = 7422) and nonpregnant women (n = 7999) who had complete demographic and anthropometric data. In addition to height, allometric models were developed for each measure that controlled for age, race, and self-reported health status.

RESULTS

After adjustment for age and race, weight scaled to height in men and women with mean (±SEE) powers of 2.29 ± 0.11 and 1.80 ± 0.07, respectively (both P < 0.001). Although univariate circumference-height models were weak or nonsignificant, when adjusted for age and race WC and HC scaled to height with powers of 0.76 ± 0.08 and 0.45 ± 0.05, respectively, in men and 0.80 ± 0.05 and 0.53 ± 0.04, respectively, in women (all P < 0.001). Age- and race-adjusted incremental increases in circumferences ranged from 0.2 to 0.5 cm per centimeter increase in height. Both WC/height and HC/height scaled negatively to height in men and women, and WC/HC scaled negatively to height in women only (all P < 0.001). Health status-adjusted models were similar.

CONCLUSIONS

Circumferences and related ratios scale significantly to height, notably after adjustment for age and race, across subjects who are representative of the US population. These observations have implications for the clinical and epidemiologic use of these anthropometric measures and indexes.

Significant associations of age, menopausal status and lifestyle factors with visceral adiposity in African-American and European-American women

BACKGROUND

Elevated visceral adiposity is strongly predictive of cardiometabolic disease, but, due to the high cost of biomedical imaging, assessment of factors contributing to normal variation in visceral (VAT) and subcutaneous (SAT) adipose tissue partitioning in large cohorts of healthy individuals are few, particularly in ethnic and racial minority populations.

OBJECTIVE

To describe age, menopausal status, smoking and physical activity differences in VAT and abdominal subcutaneous adipose tissue (ASAT) mass in African-American (AA) and European-American (EA) women.

METHODS

Magnetic resonance imaging measures of VAT and ASAT mass and VAT% (VAT/VAT+ASAT, %) were obtained from a cross-sectional sample of 617 EA and 111 AA non-diabetic women aged 18-80 years. Multivariate linear regression was used to test independent effects of the covariates.

RESULTS

VAT and VAT% were higher in EA than AA women (p < 0.01). Differences in VAT, ASAT and VAT% across age groups began in early adulthood in both ethnic groups, but the association of age with VAT% was stronger in EA women (p for interaction = 0.03). Current smokers had higher VAT and VAT% (p < 0.01) and lower TBF than non-smokers. Frequent participation in sports activities was associated with ∼30% lower VAT in older (>55 years) as well as younger ( < 40 years) women (p < 0.0001).

CONCLUSION

Greater allocation of abdominal adipose tissue into the visceral compartment occurs in EA than AA women and in older than younger women. Avoidance of cigarette smoking and frequent participation in sports activities may partially counteract this deleterious phenomenon of ageing.

Delayed onset of lactogenesis among first-time mothers is related to maternal obesity and factors associated with ineffective breastfeeding

BACKGROUND

Delayed onset of lactogenesis (OL) is most common in primiparas and increases the risk of excess neonatal weight loss, formula supplementation, and early weaning.

OBJECTIVE

We examined variables associated with delayed OL among first-time mothers who delivered at term and initiated breastfeeding (n = 431).

DESIGN

We conducted in-person interviews during pregnancy and at days 0, 3, and 7 postpartum and extracted obstetric and newborn information from medical records. We defined OL as delayed if it occurred after 72 h and used chi-square analysis to examine its association with potential risk factors across 6 dimensions: 1) prenatal characteristics, 2) maternal anthropometric characteristics, 3) labor and delivery experience, 4) newborn characteristics, 5) maternal postpartum factors, and 6) infant feeding variables. We examined independent associations by using multivariable logistic regression analysis.

RESULTS

Median OL was 68.9 h postpartum; 44% of mothers experienced delayed OL. We observed significant bivariate associations between delayed OL and variables in all 6 dimensions (P < 0.05). In a multivariate model adjusted for prenatal feeding intentions, independent risk factors for delayed OL were maternal age > or =30 y, body mass index in the overweight or obese range, birth weight >3600 g, absence of nipple discomfort between 0-3 d postpartum, and infant failing to "breastfeed well" > or =2 times in the first 24 h. Postpartum edema was significant in an alternate model excluding body mass index (P < 0.05).

CONCLUSIONS

The risk factors for delayed OL are multidimensional. Public health and obstetric and maternity care interventions are needed to address what has become an alarmingly common problem among primiparas.

Interactions between race/ethnicity and anthropometry in risk of incident diabetes: the multi-ethnic study of atherosclerosis

This study examined how adiposity influences racial/ethnic differences in diabetes incidence by exploring whether relations between anthropometric measures and incident diabetes vary by race/ethnicity. Data from the Multi-Ethnic Study of Atherosclerosis initiated in 2000 (n = 5,446 US men and women aged 45-84 years) were analyzed by using proportional hazards and Poisson regression. The diabetes incidence rate was 2/100 person-years (n = 479 cases). Interactions were present between race and anthropometry (P-interaction((race x body mass index)) = 0.002). The slope of incident diabetes per anthropometric unit was greatest for Chinese, less for whites and Hispanics, and still less for blacks. For small waist, risk of incident diabetes was <1/100 person-years for all racial/ethnic groups. At intermediate waist levels, Chinese had the highest and whites the lowest rates of incident diabetes. At the respective 95th percentiles of waist circumference, risk of incident diabetes per 100 person-years was 3.9 for Chinese (104 cm), 3.5 for whites (121 cm), 5.0 for blacks (125 cm), and 5.3 for Hispanics (121 cm). Adiposity influenced relative diabetes occurrence across racial/ethnic groups, in that Chinese had a steeper diabetes risk per unit of adiposity. However, the generally low level of adiposity in Chinese led to a relatively low diabetes occurrence.