A prospective study of sedentary behavior and changes in the body mass index distribution.

PURPOSE: We aimed to determine whether baseline sedentary behavior was associated with changes in body mass index (BMI) over 9 yr. METHODS: Participants were enrolled into the National Institutes of Health American Association of Retired Persons (NIH-AARP) Diet and Health study in 1995-1996 (median age, 63 yr), and BMI was reported at baseline and 9 yr later (n = 158,436). Sitting time (<3 (referent), 3-4, 5-6, 7-8, or ≥9 h·d), television viewing (none, <1, 1-2, 3-4, 5-6, 7-8, or ≥9 h·d), and the covariates (age, sex, race, education, smoking, moderate-to-vigorous physical activity, caloric intake, and sleep duration) were reported at baseline. We used longitudinal quantile regression to model changes at the 10th, 25th, 50th, 75th, and 90th BMI percentiles. RESULTS: More sitting at baseline was associated with additional increases in BMI over time, and the association was stronger at the upper BMI percentiles (e.g., <3 (referent) vs 5-6 h·d of sitting additional increases: 50th percentile = 0.41 kg·m and 95% confidence interval (CI) = 0.34-0.48; 90th percentile = 0.85 kg·m and 95% CI = 0.72-0.98). Similar associations were observed between more television viewing at baseline and additional increases in BMI over time (e.g., no television (referent) vs 3-4 h·d of television: 50th percentile = 1.96 kg·m and 95% CI = 1.77-2.15; 90th percentile = 2.11 kg·m and 95% CI = 1.49-2.73). CONCLUSIONS: Reducing sedentary behavior could help prevent an increase in BMI in adulthood especially at the upper percentiles of the BMI distribution and thereby reduce the prevalence of obesity.

Weight-related child behavioral interventions in Brazil: a systematic review.

CONTEXT: Between 1974 and 1997, the prevalence of overweight increased 300% among Brazilian children and adolescents. A systematic review was conducted between January 2010 and December 2011 of obesity-related interventions targeting Brazilian children and adolescents. EVIDENCE ACQUISITION: Manuscripts from 1965 to December 2010 were evaluated based on inclusion criteria including evaluating obesity-related outcomes and at least 50% of participants living in Brazil. Methods were adapted from the CDC's Community Guide. Evidence was based on the number of available studies, study design, execution, quality, and effect size. EVIDENCE SYNTHESIS: Sixteen articles were abstracted; five met final inclusion criteria. All intervention samples (range n=14-78; mean n=40.6) included overweight or obese children aged 8-17 years. The intervention duration range was 3-6 months, and dose frequency ranged from two to five times per week. Three of the five interventions included healthy eating and physical activity; two included only physical activity. Two interventions studies were rated as having greatest design suitability. Only one intervention had the greatest design suitability and a large effect size. CONCLUSIONS: Intervention approaches that combined physical activity and healthy eating had the strongest effects. However, small sample bias, 95% CIs of primary effects, and poor-to-moderate quality of research designs and implementation suggest the combined evidence is best rated as Insufficient. This prohibits the recommendation of specific strategies or settings. Findings suggest that more well-designed evidence-based childhood obesity interventions in Brazil are needed and that promising, but yet unproven, interventions should be evaluated rigorously.

Metabolism and breast cancer risk: frontiers in research and practice.

Fifty years ago the causes of cancer were largely unknown. Since then, it has become clear that a strong relationship exists between obesity and many cancers, particularly postmenopausal breast cancer. A major challenge in understanding the link between obesity and cancer risk has been elucidating the biological basis underlying the association. Although this remains unresolved, the main candidate systems linking adiposity and cancer risk are insulin and the insulin-like growth factor-1 axis, endogenous reproductive hormones, and chronic inflammation. Our purpose is to provide a mechanistic overview of the hypothesized relationship between diet, physical activity, and obesity with breast cancer risk and progression. In addition, we will provide examples of recently funded randomized clinical trials examining metabolic risk factors in relation to breast cancer risk and survival. Additional research is warranted to validate the strength and consistency of the relationships among diet, these biomarkers, and breast cancer risk. As these relationships become clearer, future studies will be needed to develop effective intervention programs to prevent breast cancer and improve cancer prognosis by promoting a healthy lifestyle.

Sedentary behavior and adiposity-associated inflammation: the Multi-Ethnic Study of Atherosclerosis.

BACKGROUND: Sedentary behavior is associated with adiposity and cardiometabolic risk. PURPOSE: To determine the associations between sedentary behavior and measures of adiposity-associated inflammation. METHODS: Between 2002 and 2005, a total of 1543 Multi-Ethnic Study of Atherosclerosis participants completed detailed health history questionnaires, underwent physical measurements, and had blood assayed for adiponectin, leptin, tumor necrosis factor-alpha (TNF-α) and resistin. Analyses included linear regression completed in 2010. The mean age was 64.3 years and nearly 50% were female. Forty-one percent were non-Hispanic white, 24% Hispanic-American, 20% African-American, and 14% Chinese-American. RESULTS: In linear regression analyses and with adjustment for age, gender, ethnicity, education, BMI, smoking, alcohol consumption, hypertension, diabetes mellitus, dyslipidemia, hormone therapy and waist circumference, sedentary behavior was associated with higher natural log ("ln") of leptin and ln TNF-α but a lower ln adiponectin-to-leptin ratio (ß=0.07, ß=0.03 and -0.07, p<0.05 for all). Compared to the first tertile, and after the same adjustment, the second and third tertiles of sedentary behavior were associated with higher levels of ln leptin (ß=0.11 and ß=0.12, respectively; p<0.05 for both) but lower levels of the adiponectin-to-leptin ratio (ß=-0.09 and -0.11, respectively; p<0.05 for both). CONCLUSIONS: Sedentary behavior is associated with unfavorable levels of adiposity-associated inflammation.

Family circumstance, sedentary behaviour and physical activity in adolescents living in England: Project STIL.

BACKGROUND: Identification of non-modifiable correlates of physical activity and sedentary behaviour in youth contributes to the development of effective targeted intervention strategies. The purpose of this research was to examine the relationships between family circumstances (e.g. socio-economic status, single vs. dual parent household, presence/absence of siblings) and leisure-time physical activity and sedentary behaviours in adolescents. METHODS: A total of 1171 adolescents (40% male; mean age 14.8 years) completed ecological momentary assessment diaries every 15 minutes for 3 weekdays outside of school hours and 1 weekend day. Analysed behaviours were sports/exercise, active travel, TV viewing, computer use, sedentary socialising (hanging-out, using the telephone, sitting and talking) and total sedentary behaviour. Linear regression was employed to estimate levels of association between individual family circumstance variables and each behaviour. RESULTS: Compared to girls from higher socioeconomic status (SES) groups, girls from low SES groups reported higher weekend TV viewing and higher weekday total sedentary behaviour. For boys, single parent status was associated with greater total sedentary behaviour compared to those from dual parent households. Boys and girls from low socio-economic neighbourhoods reported lower participation in sports/exercise compared to those living in higher socio-economic neighbourhoods. CONCLUSION: Associations were not consistent across behaviours or between genders. Overall, findings indicate that boys from single parent households and girls from low socio-economic families may be at increased risk of high sedentary behaviour. Those living in low socioeconomic neighbourhoods may be at increased risk of reduced participation in sports and exercise.

Overall obesity and abdominal adiposity as predictors of mortality in u.s. White and black adults.

PURPOSE: The association of overall obesity and abdominal adiposity in predicting risk of all-cause mortality in white and black adults was compared. METHODS: This prospective study included a national sample of 3219 non-Hispanic white and 2,561 non-Hispanic black adults 30 to 64 years of age enrolled in the third National Health and Nutrition Examination Survey during 1988-1994. Multiple measures of adiposity were measured and calculated, including body mass index (BMI), waist circumference, waist-to-hip ratio (WHR), and waist-to-thigh ratio (WTR). Vital status was ascertained with the National Death Index through 2000. RESULTS: During 12 years of follow-up (51,133 person-years), 188 white and 222 black adults died. After adjustment for age, education, smoking, and existing disease, positive dose-response associations between WTR and mortality in both sexes and races, and WHR in white and black women were observed (p(trend) < 0.05 for all). These results were unchanged after additional adjustment for BMI. In contrast, BMI and waist circumference alone exhibited curvilinear-shaped associations with mortality. A higher WTR was associated with a higher risk of mortality among normal weight (BMI: 18.5-24.9 kg/m(2)) and obese (BMI: > or =30.0 kg/m(2)) white and black adults. CONCLUSIONS: These results suggest ratio measures of abdominal adiposity, particularly WTR in both sexes and WHR in women, strongly and positively predict mortality, independent of BMI, among white and black adults. Furthermore, WTR offers additional prognostic information beyond that provided by BMI alone.

The relation of leptin and insulin with obesity-related cardiovascular risk factors in US adults.

Previous studies of leptin with cardiovascular disease (CVD) risk factors have been limited by clinical samples or lack of representation of the general population. This cross-sectional study, designed to examine whether leptin or insulin may mediate the endogenous relation of obesity with metabolic, inflammatory, and thrombogenic cardiovascular risk factors, included 522 men and 514 women aged >or=40 years who completed a physical examination during the third National Health and Nutrition Examination Survey. Participants were free of existing CVD, cancer (except non-melanoma skin cancer), diabetes, or respiratory disease. In multivariable analyses adjusted for race/ethnicity and lifestyle factors, waist circumference (WC) was positively associated with blood pressure, triglyceride, LDL cholesterol, total cholesterol:HDL ratio, apolipoprotein B, C-reactive protein (CRP), and fibrinogen concentrations, and negatively associated with HDL cholesterol and apolipoprotein A1 levels. The associations of WC with the metabolic CVD risk factors were largely attenuated after adjustment for insulin levels, while the associations of WC with the inflammatory and thrombogenic factors (CRP and fibrinogen, respectively) were largely explained by adjustment for leptin concentrations. However, leptin levels were not independently associated with CRP and fibrinogen in men and CRP in women when adjusted for WC. Positive associations of leptin and insulin with fibrinogen in women, independent of WC, were noted. These results suggest that insulin may be an important mediator of the association of obesity with metabolic but not inflammatory or thrombogenic CVD risk factors, while leptin does not appear to influence cardiovascular risk through a shared association with these risk factors. However, we cannot rule out the possibility that leptin and insulin influence cardiovascular risk in women through independent effects on fibrinogen concentrations.

Environmental interventions for eating and physical activity: a randomized controlled trial in middle schools.

BACKGROUND: Our objective was to evaluate the effects of environmental, policy, and social marketing interventions on physical activity and fat intake of middle school students on campus. DESIGN: Twenty-four middle schools were randomly assigned to intervention or control conditions. Baseline measures were collected in spring 1997, and interventions were conducted during the 1997-1998 and 1998-1999 school years SETTING/PARTICIPATION: The schools had mean enrollments of 1109, with 44.5% nonwhite students. Over 2 years, physical activity interventions were designed to increase physical activity in physical education classes and throughout the school day. Nutrition interventions were designed to provide and market low-fat foods at all school food sources, including cafeteria breakfasts and lunches, a la carte sources, school stores, and bag lunches. School staff and students were engaged in policy change efforts, but there was no classroom health education. MAIN OUTCOMES MEASURES: Primary outcomes were measured by direct observation and existing records. RESULTS: Randomized regression models (N =24 schools) revealed a significant intervention effect for physical activity for the total group (p <0.009) and boys (p <0.001), but not girls (p <0.40). The intervention was not effective for total fat (p <0.91) or saturated fat (p <0.79). Survey data indicated that the interventions reduced reported body mass index for boys (p <0.05). CONCLUSIONS: Environmental and policy interventions were effective in increasing physical activity at school among boys but not girls. The interventions were not effective in reducing fat intake at school. School environmental and policy interventions have the potential to improve health behavior of the student population, but barriers to full implementation need to be better understood and overcome.