Dane R. Van Domelen

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.

Objective measurements of daily physical activity patterns and sedentary behaviour in older adults: Age, Gene/Environment Susceptibility-Reykjavik Study

BACKGROUND objectively measured population physical activity (PA) data from older persons is lacking. The aim of this study was to describe free-living PA patterns and sedentary behaviours in Icelandic older men and women using accelerometer. METHODS from April 2009 to June 2010, 579 AGESII-study participants aged 73-98 years wore an accelerometer (Actigraph GT3X) at the right hip for one complete week in the free-living settings. RESULTS in all subjects, sedentary time was the largest component of the total wear time, 75%, followed by low-light PA, 21%. Moderate-vigorous PA (MVPA) was <1%. Men had slightly higher average total PA (counts × day(-1)) than women. The women spent more time in low-light PA but less time in sedentary PA and MVPA compared with men (P < 0.001). In persons <75 years of age, 60% of men and 34% of women had at least one bout ≥10 min of MVPA, which decreased with age, with only 25% of men and 9% of women 85 years and older reaching this. CONCLUSION sedentary time is high in this Icelandic cohort, which has high life-expectancy and is living north of 60° northern latitude.

Employment and physical activity in the U.S.

BACKGROUND Physical inactivity is a risk factor for obesity, cardiovascular disease, hypertension, and other chronic diseases that are increasingly prevalent in the U.S. and worldwide. Time at work represents a major portion of the day for employed people. PURPOSE To determine how employment status (full-time, part-time, or not employed) and job type (active or sedentary) are related to daily physical activity levels in American adults. METHODS Cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) were collected in 2003-2004 and analyzed in 2010. Physical activity was measured using Actigraph uniaxial accelerometers, and participants aged 20-60 years with ≥4 days of monitoring were included (N=1826). Accelerometer variables included mean counts/minute during wear time and proportion of wear time spent in various intensity levels. RESULTS In men, full-time workers were more active than healthy nonworkers (p=0.004), and in weekday-only analyses, even workers with sedentary jobs were more active (p=0.03) and spent less time sedentary (p<0.001) than nonworkers. In contrast with men, women with full-time sedentary jobs spent more time sedentary (p=0.008) and had less light and lifestyle intensity activity than healthy nonworkers on weekdays. Within full-time workers, those with active jobs had greater weekday activity than those with sedentary jobs (22% greater in men, 30% greater in women). CONCLUSIONS In men, full-time employment, even in sedentary occupations, is positively associated with physical activity compared to not working, and in both genders job type has a major bearing on daily activity levels.

Changes in daily activity patterns with age in U.S. men and women: National Health and Nutrition Examination Survey 2003-04 and 2005-06.

To compare daily and hourly activity patterns according to sex and age.

Association of Chronic Widespread Pain With Objectively Measured Physical Activity in Adults: Findings From the National Health and Nutrition Examination Survey

UNLABELLED Chronic widespread pain (CWP) is a common and potentially debilitating disorder. Patterns of physical activity (PA) in adults with CWP have primarily been investigated using subjective, self-report measures. The current study sought to characterize PA among community-dwelling individuals with CWP, chronic regional pain, or no chronic pain using objective measurements obtained via accelerometry in the 2003 to 2004 National Health and Nutrition Examination Survey. Data from 3,952 participants ages 20 and older were analyzed to assess relationships between pain status and objective measurements of PA. Prevalence of CWP was 3.3% and 5.4% in men and women, respectively. In men and women, the average activity counts per minute and time spent in moderate-to-vigorous PA were significantly lower for the CWP group than for the no chronic pain group. Interestingly, time spent in sedentary, light, and lifestyle activities was not associated with pain status. Statistical interaction tests indicated that the effects of chronic pain on counts per minute were stronger in men than in women. Despite recommendations for increased moderate-to-vigorous PA as a pain management strategy for CWP, results from this nationally representative study indicate that adults with CWP participate in less moderate-to-vigorous PA than individuals without chronic pain. PERSPECTIVE Using objective measurement of PA in a nationally representative sample, this study demonstrates that adults with CWP participate in reduced daily and moderate-to-vigorous PA in comparison to people with no chronic pain. Findings indicate that clinicians should emphasize the importance of increasing PA in patients with CWP.

Examining differences in physical activity levels by employment status and/or job activity level: Gender-specific comparisons between the United States and Sweden

OBJECTIVES The aim of the study was to examine the relationship between employment status and job activity level with physical activity (PA) and sedentary time, stratified by gender and country. DESIGN Cross-sectional study design. METHODS Data from working age adults (18-65 years) from two cross-sectional studies, the Swedish 2001-2002 and 2007-2008 Attitude Behavior and Change Study (ABC; n=1165) and the 2003-2006 US National Health and Nutrition Examination Survey (NHANES; n=4201), were stratified by employment status (employed and not employed) and job activity level (active, sedentary and mixed). PA in counts×min(-1) and time spent in sedentary, low and moderate or higher intensity were measured with accelerometers. Analyses were conducted in 2012-2013. RESULTS In NHANES, the employed had significantly higher counts×min(-1) and spent more time in moderate or higher intensity PA than those not employed. In ABC, no significant differences were observed between employed and unemployed. Adults with active versus sedentary occupations had higher counts×min(-1) and less sedentary time in both the USA and Sweden and in both men and women. For example, counts×min(-1) were 20-40% greater in active versus sedentary jobs. CONCLUSIONS Employment status is related to PA and sedentary time among men and women in the USA but not in Sweden. Among the employed, occupational PA is associated with total PA and sedentary time for both genders and in both countries. Comparisons of PA levels based on objective measurements can refine understanding of country differences in activity.

Association of change in brain structure to objectively measured physical activity and sedentary behavior in older adults: Age, Gene/Environment Susceptibility-Reykjavik Study.

Many studies have examined the hypothesis that greater participation in physical activity (PA) is associated with less brain atrophy. Here we examine, in a sub-sample (n=352, mean age 79.1 years) of the Age, Gene/Environment Susceptibility-Reykjavik Study cohort, the association of the baseline and 5-year change in magnetic resonance imaging (MRI)-derived volumes of gray matter (GM) and white matter (WM) to active and sedentary behavior (SB) measured at the end of the 5-year period by a hip-worn accelerometer for seven consecutive days. More GM (β=0.11; p=0.044) and WM (β=0.11; p=0.030) at baseline was associated with more total physical activity (TPA). Also, when adjusting for baseline values, the 5-year change in GM (β=0.14; p=0.0037) and WM (β=0.11; p=0.030) was associated with TPA. The 5-year change in WM was associated with SB (β=-0.11; p=0.0007). These data suggest that objectively measured PA and SB late in life are associated with current and prior cross-sectional measures of brain atrophy, and that change over time is associated with PA and SB in expected directions.

Is There a Sex Difference in Accelerometer Counts During Walking in Older Adults

BACKGROUND Accelerometers have emerged as a useful tool for measuring free-living physical activity in epidemiological studies. Validity of activity estimates depends on the assumption that measurements are equivalent for males and females while performing activities of the same intensity. The primary purpose of this study was to compare accelerometer count values in males and females undergoing a standardized 6-minute walk test. METHODS The study population was older adults (78.6 ± 4.1 years) from the AGES-Reykjavik Study (N = 319). Participants performed a 6-minute walk test at a self-selected fast pace while wearing an ActiGraph GT3X at the hip. Vertical axis counts · s(-1) was the primary outcome. Covariates included walking speed, height, weight, BMI, waist circumference, femur length, and step length. RESULTS On average, males walked 7.2% faster than females (1.31 vs. 1.22 m · s(-1), P < .001) and had 32.3% greater vertical axis counts · s(-1) (54.6 vs. 39.4 counts · s(-1), P < .001). Accounting for walking speed reduced the sex difference to 19.2% and accounting for step length further reduced the difference to 13.4% (P < .001). CONCLUSION Vertical axis counts · s(-1) were disproportionally greater in males even after adjustment for walking speed. This difference could confound free-living activity estimates.

A Discriminant Function Approach to Adjust for Processing and Measurement Error When a Biomarker is Assayed in Pooled Samples

Pooling biological specimens prior to performing expensive laboratory assays has been shown to be a cost effective approach for estimating parameters of interest. In addition to requiring specialized statistical techniques, however, the pooling of samples can introduce assay errors due to processing, possibly in addition to measurement error that may be present when the assay is applied to individual samples. Failure to account for these sources of error can result in biased parameter estimates and ultimately faulty inference. Prior research addressing biomarker mean and variance estimation advocates hybrid designs consisting of individual as well as pooled samples to account for measurement and processing (or pooling) error. We consider adapting this approach to the problem of estimating a covariate-adjusted odds ratio (OR) relating a binary outcome to a continuous exposure or biomarker level assessed in pools. In particular, we explore the applicability of a discriminant function-based analysis that assumes normal residual, processing, and measurement errors. A potential advantage of this method is that maximum likelihood estimation of the desired adjusted log OR is straightforward and computationally convenient. Moreover, in the absence of measurement and processing error, the method yields an efficient unbiased estimator for the parameter of interest assuming normal residual errors. We illustrate the approach using real data from an ancillary study of the Collaborative Perinatal Project, and we use simulations to demonstrate the ability of the proposed estimators to alleviate bias due to measurement and processing error.

A variant of sparse partial least squares for variable selection and data exploration

When data are sparse and/or predictors multicollinear, current implementation of sparse partial least squares (SPLS) does not give estimates for non-selected predictors nor provide a measure of inference. In response, an approach termed “all-possible” SPLS is proposed, which fits a SPLS model for all tuning parameter values across a set grid. Noted is the percentage of time a given predictor is chosen, as well as the average non-zero parameter estimate. Using a “large” number of multicollinear predictors, simulation confirmed variables not associated with the outcome were least likely to be chosen as sparsity increased across the grid of tuning parameters, while the opposite was true for those strongly associated. Lastly, variables with a weak association were chosen more often than those with no association, but less often than those with a strong relationship to the outcome. Similarly, predictors most strongly related to the outcome had the largest average parameter estimate magnitude, followed by those with a weak relationship, followed by those with no relationship. Across two independent studies regarding the relationship between volumetric MRI measures and a cognitive test score, this method confirmed a priori hypotheses about which brain regions would be selected most often and have the largest average parameter estimates. In conclusion, the percentage of time a predictor is chosen is a useful measure for ordering the strength of the relationship between the independent and dependent variables, serving as a form of inference. The average parameter estimates give further insight regarding the direction and strength of association. As a result, all-possible SPLS gives more information than the dichotomous output of traditional SPLS, making it useful when undertaking data exploration and hypothesis generation for a large number of potential predictors.