Sarah M. Camhi

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.

Sedentary behavior and cardiovascular morbidity and mortality: A science advisory from the American Heart Association

Epidemiological evidence is accumulating that indicates greater time spent in sedentary behavior is associated with all-cause and cardiovascular morbidity and mortality in adults such that some countries have disseminated broad guidelines that recommend minimizing sedentary behaviors. Research examining the possible deleterious consequences of excess sedentary behavior is rapidly evolving, with the epidemiology-based literature ahead of potential biological mechanisms that might explain the observed associations. This American Heart Association science advisory reviews the current evidence on sedentary behavior in terms of assessment methods, population prevalence, determinants, associations with cardiovascular disease incidence and mortality, potential underlying mechanisms, and interventions. Recommendations for future research on this emerging cardiovascular health topic are included. Further evidence is required to better inform public health interventions and future quantitative guidelines on sedentary behavior and cardiovascular health outcomes.

Leisure Time Sedentary Behavior, Occupational/Domestic Physical Activity, and Metabolic Syndrome in U.S. Men and Women

BACKGROUND This study examines leisure time sedentary behavior (LTSB) and usual occupational/domestic activity (UODA) and their relationship with metabolic syndrome and individual cardiovascular disease (CVD) risk factors, independent of physical activity level. METHODS National Health and Nutrition Examination Survey (NHANES) 2003-2006 data from men (n = 1868) and women (n = 1688) with fasting measures were classified as having metabolic syndrome by the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) definition. LTSB was determined from self-reported television viewing and computer usage. UODA was self-reported daily behavior (sitting, standing, walking, carrying loads). RESULTS LTSB >or=4 hours/day was associated with odds of having metabolic syndrome of 1.94 (95% confidence interval [CI], 1.24, 3.03) in men compared to <or=1 hour/day. LTSB >or=4 hour/day was also associated with higher odds of elevated waist circumference (1.88, CI, 1.03, 3.41), low high-density lipoprotein cholesterol (HDL-C) (1.84, CI, 1.35, 2.51), and high blood pressure (1.55, CI, 1.07, 2.24) in men. LTSB 2-3 hours/day was associated with higher odds of elevated glucose (1.32, CI, 1.00, 1.75) in men. In women, odds of metabolic syndrome were 1.54 (CI, 1.00, 2.37) with >or=4 hours/day LTSB, but LTSB was not associated with risk of the individual CVD risk factors. Higher LTSB was associated with metabolic syndrome in inactive men (1.50, CI, 1.07, 2.09), active men (1.74, CI, 1.11, 2.71), inactive women (1.69, CI, 1.24, 2.33), but not active women (1.62, CI, 0.87,3.01). UODA was not strongly associated with metabolic syndrome or CVD risk factors in either men or women. CONCLUSIONS In men, high LTSB is associated with higher odds of metabolic syndrome and individual CVD risk factors regardless of meeting physical activity recommendations. In women, high LTSB is associated with higher odds of metabolic syndrome only in those not meeting the physical activity recommendations.

Tracking of cardiometabolic risk factor clustering from childhood to adulthood.

Cardiometabolic risk factor clustering is predictive of future cardiovascular disease. If clustering of risk factors is a stable characteristic from childhood to adulthood, then intervention in high-risk children may provide an early opportunity to decrease the progression to overt cardiovascular disease outcomes. Thus, the purpose of this paper was to review the evidence for risk factor clustering being a stable characteristic from childhood to adulthood. Seven articles were identified that met the inclusion criteria. Despite varying definitions of risk factor clustering and different methodologies for assessing tracking, the results generally showed stability of risk factor clustering from childhood into adulthood. Inter-age correlations of risk factor cluster scores ranged from 0.42 to 0.67, and the proportions of individuals remaining in the upper quantiles of risk over time were significantly greater than predicted by chance alone. Future studies are needed to elucidate the effects of gender, ethnicity, and lifestyle behaviors on the tracking of risk factor clustering.

A catalog of rules, variables, and definitions applied to accelerometer data in the National Health and Nutrition Examination Survey, 2003-2006.

Introduction The National Health and Nutrition Examination Survey (NHANES) included accelerometry in the 2003–2006 data collection cycles. Researchers have used these data since their release in 2007, but the data have not been consistently treated, examined, or reported. The objective of this study was to aggregate data from studies using NHANES accelerometry data and to catalogue study decision rules, derived variables, and cut point definitions to facilitate a more uniform approach to these data. Methods We conducted a PubMed search of English-language articles published (or indicated as forthcoming) from January 2007 through December 2011. Our initial search yielded 74 articles, plus 1 article that was not indexed in PubMed. After excluding 21 articles, we extracted and tabulated details on 54 studies to permit comparison among studies. Results The 54 articles represented various descriptive, methodological, and inferential analyses. Although some decision rules for treating data (eg, criteria for minimal wear-time) were consistently applied, cut point definitions used for accelerometer-derived variables (eg, time spent in various intensities of physical activity) were especially diverse. Conclusion Unique research questions may require equally unique analytical approaches; some inconsistency in approaches must be tolerated if scientific discovery is to be encouraged. This catalog provides a starting point for researchers to consider relevant and/or comparable accelerometer decision rules, derived variables, and cut point definitions for their own research questions.

Accelerometer-Determined Steps/Day and Metabolic Syndrome

BACKGROUND There is a lack of knowledge about the relationship between objectively measured physical activity and the odds of having metabolic syndrome (MetS) and cardiovascular (CVD) risk factors. PURPOSE This study aims to investigate associations between accelerometer-determined steps/day and the odds of having MetS and its individual CVD risk factors in the U.S. population. METHODS Adults in 2005-2006 NHANES with accelerometer-determined steps/day and measurements necessary to determine MetS by AHA/NHLBI were included (n=1446, 48.2% men, 33.5% with MetS, mean age=47.5 years, mean BMI=28.7 kg/m(2)). Logistic regression was used to estimate the odds of having MetS or abnormal CVD risk factors from incrementally higher levels of steps/day. RESULTS MetS prevalence decreased as steps/day increased (p<0.0001), with 55.7% of participants in the lowest categoric level of steps/day and 13.3% in the highest level having MetS. The odds of having MetS were 10% lower for each additional 1000 steps/day (OR=0.90, 95% CI=0.86, 0.93). The likelihood of having MetS was OR=0.28 (95% CI=0.18, 0.44) for active to highly active and 0.60 (0.43, 0.82) for low to somewhat-active compared to sedentary adults (p<0.0001). Adults who took more steps/day tended to have lower waist circumference, higher high-density lipoprotein (HDL) cholesterol level, and lower levels of triglycerides. CONCLUSIONS Adults who maintain an active lifestyle by accumulating more steps are likely to have a lower prevalence of MetS and its individual CVD risk factors. Although other concomitant lifestyle behaviors may influence this lower prevalence, the evidence presented here on steps/day and metabolic syndrome, and elsewhere on physical activity and other health and disease states, suggest that it is a fundamental component of daily living.

Accelerometer-determined moderate intensity lifestyle activity and cardiometabolic health

OBJECTIVE Objective To assess the relationship between moderate intensity lifestyle activity (LA) and cardiometabolic health using accelerometer data from the National Health and Nutrition Examination Survey (NHANES) 2005-2006. METHODS One thousand three hundred and seventy-one adults (50% men; 71% non-Hispanic white) provided valid data to quantify time in LA [760-2019 counts per minute (CPM)] and moderate-to-vigorous physical activity (MVPA; ≥ 2020 CPM). Associations between LA [minutes per day (min/day); steps per day (steps/day)], and cardiometabolic risk factors [triglycerides, HDL-cholesterol (HDL-C), blood pressure, glucose, waist circumference], metabolic syndrome, self-reported hypertension and diabetes were investigated using logistic regression. Analyses were adjusted for age, gender, race/ethnicity, and MVPA categories. RESULTS Greater time in LA (min/day), independent from MVPA, was associated with lower odds of elevated triglycerides (OR, 95% CI per 30 LA minutes: (0.88, 0.80-0.98), low HDL-C (0.88, 0.83-0.94), elevated waist circumference (0.89, 0.84-0.95), metabolic syndrome (0.88, 0.80-0.97), and diabetes (0.65, 0.51-0.83) [corrected]. The same cardiometabolic risk factors were also significantly associated with LA steps/day. No significant association was found between LA (min/day or steps/day) and glucose or blood pressure. CONCLUSION Accumulation of time or steps in LA is independently related to lower odds for certain cardiometabolic risk factors. Research should consider the effects of increasing LA, which could influence future physical activity recommendations.

Patterns of adult stepping cadence in the 2005-2006 NHANES.

OBJECTIVE Laboratory studies of adult walking behavior have consistently found that a cadence of 100 steps/min is a reasonable threshold for moderate intensity. The purpose of this study was to determine cadence patterns in free-living adults, and in particular, time spent at increasing cadence increments including 100 steps/min and beyond. METHOD 3744 adults ≥20 years provided at least one valid day (minimally 10/24 h of wear) of minute-by-minute accelerometer-determined step data during the 2005-2006 U.S. National Health and Nutrition Examination Survey (NHANES). Means for time spent (min/day) and steps/day were calculated for 8 cadence categories including zero and each incremental cadence band thereafter beginning with 1-19 through 100-119, and beyond to 120+steps/min. RESULTS U.S. adults accumulate ≅4.8 h/day of zero cadence during wearing time, ≅8.7 h between 1 and 59 steps/min, ≅16 min/day at cadences of 60-79 steps/min, ≅8 min at 80-99 steps/min, ≅5 min at 100-119 steps/min, and ≅2 min at 120+steps/min. CONCLUSION Self-selected walking at 100+steps/min was a rare phenomenon in this large free-living sample of the U.S. population, but study participants did accumulate ≅30 min/day at cadences of 60+steps/min.

Changes in C-reactive protein from low-fat diet and/or physical activity in men and women with and without metabolic syndrome

Change in high-sensitivity C-reactive protein (CRP) from low-fat diet (diet) and physical activity (PA) interventions is relatively unknown for adults with metabolic syndrome. The objective of the study was to assess CRP change (DeltaCRP) with diet and/or PA in men and women with and without metabolic syndrome. Men (n = 149) and postmenopausal women (n = 125) with elevated low-density lipoprotein cholesterol and low high-density lipoprotein cholesterol were recruited into a 1-year randomized controlled trial. Treatment groups were as follows: control, diet (reduced total fat, saturated fat, and cholesterol intake), PA (45-60 minutes at 60%-85% maximum heart rate), or diet + PA. Weight loss was not an intervention focus. Metabolic syndrome was defined using the American Heart Association/National Heart, Lung, and Blood Institute criteria. Stored plasma samples were analyzed for CRP. Change in CRP was compared between treatments, within sex and metabolic syndrome status, using analysis of covariance, including covariates for baseline CRP and body fat change. For women with metabolic syndrome (n = 39), DeltaCRP was greater in diet vs control (-1.2 +/- 0.4, P = .009), diet + PA vs control (-1.3 +/- 0.4, P = .006), and diet + PA vs PA (-1.1 +/- 0.4, P = .02). Women with metabolic syndrome receiving the diet component (diet or diet + PA) had greater DeltaCRP compared with those who did not (control or PA) (P = .001). Change in CRP was not significantly different between intervention groups in men overall, women overall, men with (n = 47) or without metabolic syndrome (n = 102), or women without metabolic syndrome (n = 86). Low-fat diet may be the most effective treatment for reducing CRP in women with metabolic syndrome.

Physical Activity and Screen Time in Metabolically Healthy Obese Phenotypes in Adolescents and Adults

Introduction. The purpose of this study was to examine levels of physical activity (PA) and screen time (ST) in metabolically healthy obese (MHO) and metabolically unhealthy obese (MUO) adolescents and adults. Methods. NHANES data from obese adolescents (12–18 years, BMI z-score ≥ 95th percentile) and adults (19–85 years, BMI ≥ 30 kg/m2) were pooled from 2003–2005 cycles. Metabolic phenotypes were categorized as MHO (0 or 1 cardiometabolic risk factor; triglycerides, HDL-C, blood pressure, or glucose) or MUO (≥2 cardiometabolic risk factors). Logistic regression models estimated associations between phenotype and PA/ST adjusted for age, gender, BMI, race/ethnicity, menopausal status, and NHANES cycle. Results. Among adolescents, PA was not associated with MHO. In contrast, MHO adults 19–44 years were 85% more likely to engage in active transportation and 2.7 times more likely to be involved in light intensity usual daily activity versus sitting. For each minute per day, adults 45–85 years were 36% more likely to have the MHO phenotype with higher levels of moderate PA. ST was not associated with metabolic phenotypes in adolescents or adults. Conclusion. The current study provides evidence that PA, but not ST, differs between MHO and MUO in adults, but not in adolescents. Future studies are needed to confirm results.