David Berrigan

Reaction norms for age and size at maturity in response to temperature: A puzzle for life historians.

Ectotherms mature later at smaller size when growth rates are lowered by reductions in food quality but they mature later at larger sizes when growth rate is lowered by reductions in temperature. We argue that this general pattern has been neglected by life history theorists and suggest that an explanation for these strikingly different responses to two environmental cues might be found by considering correlations between the growth coefficient of the Bertalanffy equation and asymptotic size in a model for the evolution of age and size at maturity

Sedentary Activity Associated With Metabolic Syndrome Independent of Physical Activity

OBJECTIVE This study examined the association between objectively measured sedentary activity and metabolic syndrome among older adults. RESEARCH DESIGN AND METHODS Data were from 1,367 men and women, aged ≥60 years who participated in the 2003–2006 National Health and Nutrition Examination Survey (NHANES). Sedentary time during waking hours was measured by an accelerometer (<100 counts per minute). A sedentary bout was defined as a period of time >5 min. A sedentary break was defined as an interruption in sedentary time (≥100 counts per minute). Metabolic syndrome was defined according to the Adult Treatment Panel (ATP) III criteria. RESULTS On average, people spent 9.5 h (65% of wear time) as sedentary. Compared with people without metabolic syndrome, people with metabolic syndrome spent a greater percentage of time as sedentary (67.3 vs. 62.2%), had longer average sedentary bouts (17.7 vs. 16.7 min), had lower intensity during sedentary time (14.8 vs. 15.8 average counts per minute), and had fewer sedentary breaks (82.3 vs. 86.7), adjusted for age and sex (all P < 0.01). A higher percentage of time sedentary and fewer sedentary breaks were associated with a significantly greater likelihood of metabolic syndrome after adjustment for age, sex, ethnicity, education, alcohol consumption, smoking, BMI, diabetes, heart disease, and physical activity. The association between intensity during sedentary time and metabolic syndrome was borderline significant. CONCLUSIONS The proportion of sedentary time was strongly related to metabolic risk, independent of physical activity. Current results suggest older people may benefit from reducing total sedentary time and avoiding prolonged periods of sedentary time by increasing the number of breaks during sedentary time.

Patterns of health behavior in U.S. adults

BACKGROUND Associations between health-related behaviors are important for two reasons. First, disease prevention and health promotion depend on understanding both prevalence of health behaviors and associations among such behaviors. Second, behaviors may have synergistic effects on disease risk. METHODS We document patterns of adherence to recommendations concerning five behaviors (physical activity, tobacco use, alcohol consumption, fruit and vegetable consumption, and dietary fat intake) in U.S. adults (n = 15,425) using data from the Third National Health and Nutrition Examination Survey. Division of individuals into categories associated with adherence or nonadherence to lifestyle recommendations results in 32 patterns of adherence/nonadherence. RESULTS Proportions of U.S. adults with 21 of 32 behavior patterns characterized here deviated from proportions expected if health behaviors are independent of each other. The two extreme patterns, all adherence (5.9%) and all nonadherence (4.9%), were found in about double the proportion expected. Age, gender, race/ethnicity, education, and income were associated with a number of patterns, including the two extremes. CONCLUSIONS This analysis of behavior patterns highlights population subgroups of public health importance, provides a benchmark for studies of multivariate associations between health behaviors, and supports a multidimensional model of health behavior.

The association between urban form and physical activity in U.S. adults

BACKGROUND Physical inactivity is associated with multiple adverse health outcomes. Results from the transportation literature suggest that aspects of the urban environment may influence walking for transportation. In this paper we examine the association between a proxy measure of the urban environment and walking behavior. METHODS We analyzed the association between home age and walking behavior in U.S. adults using data from the Third National Health and Nutrition Examination Survey. Logistic regression was used to estimate odds ratios and 95% confidence intervals and to control for the effects of gender, race/ethnicity, age, education level, household income, and activity limitations. RESULTS Adults who lived in homes built before 1946 and from 1946 to 1973 were significantly more likely to walk 1+ miles > or =20 times per month than those who lived in homes built after 1973. This association was present among people living in urban and suburban counties, but absent among those living in rural counties. The association was also found in models that controlled for gender, race/ethnicity, age, education, income, and any health-related activity limitation. Other forms of leisure-time physical activity were not independently associated with home age. CONCLUSIONS These results support the hypothesis that environmental variables influence walking frequency and suggest that home age may be a useful proxy for features of the urban environment that influence physical activity in the form of walking. Such proxy measures could facilitate testing ecologic models of health behavior using survey data.

Temperature, demography, and ectotherm fitness.

Temperature has profound effects on ectotherms such as plants, invertebrates, and lower vertebrates (Hochachka and Somero 1984; Cossins and Bowler 1987). The impact of temperature is often depicted graphically as a “thermal performance curve,” which plots performance as a function of body temperature (Huey and Stevenson 1979). Typically, performance increases gradually with temperature up to some maximal or optimal level but then declines precipitously as temperature approaches damaging levels and upper lethal limits. The impact of temperature on Darwinian fitness of ectotherms can be depicted similarly. However, one must first choose an appropriate measure of fitness (Stearns 1982). Several measures are available (Tuljupurkar 1990; Roff 1992; Stearns 1992; Carey 1993; Kozlowski 1993; Charlesworth 1994), but r (“intrinsic rate of increase”; see “Material and Methods”) and Ro (“net reproductive rate”; see “Material and Methods”) are by far the two most commonly used ones. The intrinsic rate of increase is the rate of population increase in a closed population, assuming constant age-specific schedules of death and reproduction and a stable age distribution, whereas the net reproductive rate is the average number of female offspring born to a female over her lifetime, again assuming constant agespecific schedules of death and reproduction (Carey 1993). Both measures estimate population growth rates, but r is scaled to time, whereas Ro is scaled per generation and is independent of time. Surprisingly, however, whether these

Levels and Patterns of Objectively Assessed Physical Activity—A Comparison Between Sweden and the United States

This study compares levels and patterns of objectively assessed physical activity in Sweden and the United States by using identical accelerometer metrics. Data of adult respondents with > or =4 days with > or =10 hours per day of accelerometer wear from Sweden (2001-2002, n = 1,172) and the United States (2003-2004, n = 2,925) were compared. Outcomes reported by age and body mass index within sex include accelerometer counts per minute and amounts and bouts of activity at different intensities, that is, sedentary, low, lifestyle, and moderate or higher intensity physical activity. The mean counts per minute were 375 (95% confidence interval (CI): 360, 390) and 377 (95% CI: 363, 391) for Swedish and US males, respectively, and 363 (95% CI: 347, 379) and 298 (95% CI: 289, 307) for Swedish and US females. Older respondents and those with higher body mass index had lower activity levels. Swedish and US males spent 36 (95% CI: 34, 38) and 33 (95% CI: 31, 36) minutes per day, and Swedish and US females spent 32 (95% CI: 29, 34) and 19 (95% CI: 17, 21) minutes per day in moderate or higher intensity physical activity. Older Swedes were more active in moderate or higher intensity activities than were older US respondents. However, younger Swedish males had more sedentary behavior time than did younger US males. These results provide a framework for international comparisons of physical activity levels and patterns, and they represent strong evidence for the importance of investment in objective measurement of physical activity.

Association of Sedentary Time with Mortality Independent of Moderate to Vigorous Physical Activity

Background Sedentary behavior has emerged as a novel health risk factor independent of moderate to vigorous physical activity (MVPA). Previous studies have shown self-reported sedentary time to be associated with mortality; however, no studies have investigated the effect of objectively measured sedentary time on mortality independent of MVPA. The objective our study was to examine the association between objectively measured sedentary time and all-cause mortality. Methods 7-day accelerometry data of 1906 participants aged 50 and over from the U.S. nationally representative National Health and Nutrition Examination Survey (NHANES) 2003–2004 were analyzed. All-cause mortality was assessed from the date of examination through December 31, 2006. Results Over an average follow-up of 2.8 years, there were 145 deaths reported. In a model adjusted for sociodemographic factors, lifestyle factors, multiple morbidities, mobility limitation, and MVPA, participants in third quartile (hazard ratio (HR):4.05; 95%CI:1.55–10.60) and fourth quartile (HR:5.94; 95%CI: 2.49–14.15) of having higher percent sedentary time had a significantly increased risk of death compared to those in the lowest quartile. Conclusions Our study suggests that sedentary behavior is a risk factor for mortality independent of MVPA. Further investigation, including studies with longer follow-up, is needed to address the health consequences of sedentary behavior.

Thermodynamics Constrains the Evolution of Insect Population Growth Rates: “Warmer Is Better”

Diverse biochemical and physiological adaptations enable different species of ectotherms to survive and reproduce in very different temperature regimes, but whether these adaptations fully compensate for the thermodynamically depressing effects of low temperature on rates of biological processes is debated. If such adaptations are fully compensatory, then temperature‐dependent processes (e.g., digestion rate, population growth rate) of cold‐adapted species will match those of warm‐adapted species when each is measured at its own optimal temperature. Here we show that cold‐adapted insect species have much lower maximum rates of population growth than do warm‐adapted species, even when we control for phylogenetic relatedness. This pattern also holds when we use a structural‐equation model to analyze alternative hypotheses that might otherwise explain this correlation. Thus, although physiological adaptations enable some insects to survive and reproduce at low temperatures, these adaptations do not overcome the “tyranny” of thermodynamics, at least for rates of population increase. Indeed, the sensitivity of population growth rates of insects to temperature is even greater than predicted by a recent thermodynamic model. Our findings suggest that adaptation to temperature inevitably alters the population dynamics of insects. This result has broad evolutionary and ecological consequences.

Physical Activity in US Youth: Effect of Race/Ethnicity, Age, Gender, and Weight Status

PURPOSE To describe physical activity (PA) levels by race/ethnicity, age, gender, and weight status in a representative sample of US youth. METHODS Cross-sectional data from the 2003-2004 and 2005-2006 National Health and Nutrition Examination Survey were combined and analyzed. Youth aged 6-19 yr with at least four 10-h days of PA measured by accelerometry were included (n = 3106). Outcomes included mean counts per minute and minutes spent in moderate-to-vigorous PA (MVPA). RESULTS Among the groups, the 6- to 11-yr-olds spent more time (88 min·d) in MVPA than the 12- to 15-yr-olds (33 min·d) and 16- to 19-yr-olds (26 min·d; P < 0.001 for both). Females spent fewer minutes per day in MVPA than males (P < 0.001). Overall, obese youth spent 16 fewer minutes per day in MVPA than normal-weight youth. However, non-Hispanic white males spent three to four fewer minutes per day in vigorous PA than Mexican American (MA; P = 0.004) and non-Hispanic black (P < 0.001) males but had lower obesity rates and obese 12- to 15-yr-old MA recorded similar minutes in MVPA per day as normal-weight MA (P > 0.050). There was a significant three-way age-body mass index-race/ethnicity interaction for mean minutes per day in MVPA (P < 0.001). Adjustment for total energy intake did not qualitatively alter these results. CONCLUSIONS Females and older youth were the least active groups. Obese youth were generally less active, but this did not hold uniformly across race/ethnic groups. Cultural or biological factors could moderate the association between PA and obesity in youth.

Self-reported and Objectively Measured Activity Related to Biomarkers Using Nhanes

PURPOSE The purpose of this study was to examine the independent associations of self-reported and objectively measured (using accelerometers) moderate to vigorous physical activity (MVPA) with physiological and anthropometric biomarkers in a nationally representative sample of U.S. adults. METHODS Data from the cross-sectional National Health and Nutrition Examination Survey 2003-2006 data were analyzed. Adults 20 yr and older (N=5797) with self-reported PA and 4 d or more of accelerometer data were included in the analyses. Pregnant or lactating women were excluded. Outcomes were blood pressure, body mass index, waist circumference, triceps and subscapular skinfolds, cholesterol, triglyceride, C-reactive protein, homocysteine, and insulin resistance and hyperinsulinemia indices. RESULTS Objectively measured MVPA displayed stronger independent associations with the biomarkers than did self-reported MVPA, even after adjusting for sociodemographic and health factors (adjusted Wald F values=3.9-85.6, P<0.05-0.0001). Self-reported and objectively measured MVPA were independently associated with skinfold measures, HDL, and C-reactive protein when both were included in the model. CONCLUSIONS Objectively measured MVPA displayed stronger associations with physiological and anthropometric biomarkers than self-reported MVPA. However, self-reported and objectively measured MVPA appear to capture distinct aspects of PA that are independently associated with certain biomarkers. Further understanding of the distinct contributions of self-reported and objectively measured PA to health outcomes could help to better identify optimal activity level and pattern.