Sam Leary

Objective measurement of levels and patterns of physical activity

Objective: To measure the levels and patterns of physical activity, using accelerometers, of 11-year-old children participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Design: Cross-sectional analysis. Setting: ALSPAC is a birth cohort study located in the former county of Avon, in the southwest of England. This study used data collected when the children were 11 years old. Participants: 5595 children (2662 boys, 2933 girls). The children are the offspring of women recruited to a birth cohort study during 1991–2. The median age (95% CI) of the children is now 11.8 (11.6 to 11.9) years. Methods: Physical activity was measured over a maximum of 7 consecutive days using the MTI Actigraph accelerometer. Main outcome measures: Level and pattern of physical activity. Results: The median physical activity level was 580 counts/min. Boys were more active than girls (median (IQR) 644 (528–772) counts/min vs 529 (444–638) counts/min, respectively). Only 2.5% (95% CI 2.1% to 2.9%) of children (boys 5.1% (95% CI 4.3% to 6.0%), girls 0.4% (95% CI 0.2% to 0.7%) met current internationally recognised recommendations for physical activity. Children were most active in summer and least active in winter (difference = 108 counts/min). Both the mother and partner’s education level were inversely associated with activity level (p for trend <0.001 (both mother and partner)). The association was lost for mother’s education (p for trend = 0.07) and attenuated for partner’s education (p for trend = 0.02), after adjustment for age, sex, season, maternal age and social class. Conclusions: A large majority of children are insufficiently active, according to current recommended levels for health.

Objectively measured physical activity and fat mass in a large cohort of children

Background Previous studies have been unable to characterise the association between physical activity and obesity, possibly because most relied on inaccurate measures of physical activity and obesity. Methods and Findings We carried out a cross sectional analysis on 5,500 12-year-old children enrolled in the Avon Longitudinal Study of Parents and Children. Total physical activity and minutes of moderate and vigorous physical activity (MVPA) were measured using the Actigraph accelerometer. Fat mass and obesity (defined as the top decile of fat mass) were measured using the Lunar Prodigy dual x-ray emission absorptiometry scanner. We found strong negative associations between MVPA and fat mass that were unaltered after adjustment for total physical activity. We found a strong negative dose-response association between MVPA and obesity. The odds ratio for obesity in adjusted models between top and the bottom quintiles of minutes of MVPA was 0.03 (95% confidence interval [CI] 0.01–0.13, p-value for trend <0.0001) in boys and 0.36 (95% CI 0.17–0.74, p-value for trend = 0.006) in girls. Conclusions We demonstrated a strong graded inverse association between physical activity and obesity that was stronger in boys. Our data suggest that higher intensity physical activity may be more important than total activity.

Prospective associations between objective measures of physical activity and fat mass in 12-14 year old children: the Avon Longitudinal Study of Parents and Children (ALSPAC)

Objective To investigate associations between physical activity at age 12 and subsequent adiposity at age 14. Design Prospective birth cohort study with data collected between 2003 and 2007. Setting Original recruitment in 1991-2 of 14 541 pregnant women living in the former County of Avon (United Kingdom). Participants At age 12, 11 952 children were invited to attend the research clinic. Of these, 7159 attended, and 4150 (1964 boys, 2186 girls) provided sufficient data on exposure, outcome, and confounding variables. Main outcome measure Fat mass at age 14, measured by dual emission x ray absorptiometry, associated with physical activity at age 12, measured by accelerometry. Results Prospective associations of fat mass at age 14 (outcome) with physical activity at age 12 (exposure) were strong for both total activity (accelerometer counts/min) and for daily amount of moderate-vigorous physical activity (min/day). An extra 15 minutes of moderate-vigorous physical activity per day at age 12 was associated with lower fat mass at age 14 in boys (by 11.9% (95% confidence interval 9.5% to 14.3%)) and girls (by 9.8% (6.7% to 12.8%)). The proportion of physical activity due to moderate-vigorous physical activity was between 20% and 30% in boys and girls at the two ages. Conclusions Higher levels of physical activity, in particular activity of moderate to higher intensities, are prospectively associated with lower levels of fat mass in early adolescence. Interventions to raise levels of physical activity in children are likely to be important in the fight against obesity.

Calibration of an accelerometer during free-living activities in children

OBJECTIVE The aims of this study were to develop an equation to predict energy expenditure and to derive cut-points for moderate and vigorous physical activity intensity from the Actigraph accelerometer output in children aged 12 years. METHODS The children performed a series of activities (lying, sitting, slow walking, fast walking, hopscotch and jogging) while wearing an Actigraph and a portable metabolic unit. The sample was divided into a developmental and a validation group. Random intercepts models were used to develop a prediction equation in the developmental group. The equation was assessed in the validation group by calculating limits of agreement (actual minus predicted energy expenditure). Thresholds for moderate and vigorous activity were derived by refitting the energy expenditure model with VO2 as the outcome. RESULTS The developmental group comprised 163 children, while the validation group comprised 83 children. The equation, adjusted for age and gender, adequately predicted energy expenditure from accelerometer counts. Physical activity intensity cut-points were derived from resting VO2. The lower threshold for moderate intensity (four METs), adjusted for age and gender, was 3581 counts per minute. The lower threshold for vigorous activity (six METs) was 6130 counts per minute. CONCLUSION The prediction equation and the derived cut-points will help to better interpret the output of the Actigraph in children aged 12 years. The cut-point for moderate to vigorous physical activity is higher than that reported previously.

Is there an intrauterine influence on obesity? Evidence from parent–child associations in the Avon Longitudinal Study of Parents and Children (ALSPAC)

Background: It has been suggested that increasing obesity levels in young women lead to intrauterine environments that, in turn, stimulate increased obesity among their offspring, generating an intergenerational acceleration of obesity levels. If this mechanism is important, the association of maternal body mass index (BMI) with offspring BMI should be stronger than the association of paternal with offspring BMI. Objective: To compare the relative strengths of association of maternal and paternal BMI with offspring BMI at age 7.5, taking into account the possible effect of non-paternity. Methods: We compared strength of association for maternal–offspring and paternal–offspring BMI for 4654 complete parent–offspring trios in the Avon Longitudinal Study of Parents and Children (ALSPAC), using unstandardised and standardised regression analysis. We carried out a sensitivity analysis to investigate the influence of non-paternity on these associations. Results: The strength of association between parental BMI and offspring BMI at age 7.5 was similar for both parents. Taking into account correlations between maternal and paternal BMI, performing standardised rather than unstandardised regression and carrying out a sensitivity analysis for non-paternity emphasised the robustness of the general similarity of the associations. The associations between high parental BMI (top decile) and offspring BMI are also similar for both parents. Conclusion: Comparison of mother–offspring and father–offspring associations for BMI suggests that intergenerational acceleration mechanisms do not make an important contribution to levels of childhood BMI within the population. Associations at later ages and for different components of body composition now require study.

Exploring the Developmental Overnutrition Hypothesis Using Parental–Offspring Associations and FTO as an Instrumental Variable

Background The developmental overnutrition hypothesis suggests that greater maternal obesity during pregnancy results in increased offspring adiposity in later life. If true, this would result in the obesity epidemic progressing across generations irrespective of environmental or genetic changes. It is therefore important to robustly test this hypothesis. Methods and Findings We explored this hypothesis by comparing the associations of maternal and paternal pre-pregnancy body mass index (BMI) with offspring dual energy X-ray absorptiometry (DXA)–determined fat mass measured at 9 to 11 y (4,091 parent–offspring trios) and by using maternal FTO genotype, controlling for offspring FTO genotype, as an instrument for maternal adiposity. Both maternal and paternal BMI were positively associated with offspring fat mass, but the maternal association effect size was larger than that in the paternal association in all models: mean difference in offspring sex- and age-standardised fat mass z-score per 1 standard deviation BMI 0.24 (95% confidence interval [CI]: 0.22 to 0.26) for maternal BMI versus 0.13 (95% CI: 0.11, 0.15) for paternal BMI; p-value for difference in effect < 0.001. The stronger maternal association was robust to sensitivity analyses assuming levels of non-paternity up to 20%. When maternal FTO, controlling for offspring FTO, was used as an instrument for the effect of maternal adiposity, the mean difference in offspring fat mass z-score per 1 standard deviation maternal BMI was −0.08 (95% CI: −0.56 to 0.41), with no strong statistical evidence that this differed from the observational ordinary least squares analyses (p = 0.17). Conclusions Neither our parental comparisons nor the use of FTO genotype as an instrumental variable, suggest that greater maternal BMI during offspring development has a marked effect on offspring fat mass at age 9–11 y. Developmental overnutrition related to greater maternal BMI is unlikely to have driven the recent obesity epidemic.

Sedentary Behavior and Obesity in a Large Cohort of Children

The purpose of this study was to examine the association between sedentary behavior and obesity among 12‐year‐old children, while adjusting for moderate‐to‐vigorous physical activity (MVPA) and other potential confounding variables. Cross‐sectional analyses were carried out with data from 5,434 children who participated in the Avon Longitudinal Study of Parents and Children (ALSPAC). Fat mass was derived using dual‐energy X‐ray emission absorptiometry, and height and weight measurements were used to calculate BMI (kg/m2). The children wore an accelerometer for 7 days. The cut points for sedentary behavior and MVPA were ≤199 and ≥3,600 counts per minute (cpm), respectively. Logistic regression analyses were performed to estimate odds ratios (ORs), adjusting for potential confounders of physical activity that included gender, social factors, early life factors, and maturation. The minimally adjusted association between sedentary behavior and obesity was positive, OR = 1.18 (1.08, 1.28). After adjusting for the series of potential confounders of physical activity the positive association remained, OR = 1.32 (1.14, 1.53). The crude association between 15 min of MVPA per day and obesity was negative, OR = 0.54 (0.48, 0.62). When 15 min of MVPA per day was additionally controlled for in the models, the positive associations between sedentary behavior and obesity were negated. Sedentary behavior was positively associated with obesity in the 12‐year‐old children, but this association was not independent of MVPA; low levels of MVPA among the sedentary children increased the odds of obesity. These findings support the importance of specifically engaging in MVPA during childhood to reduce the prevalence of obesity.

Diet in childhood and adult cardiovascular and all cause mortality: the Boyd Orr cohort

Objective: To examine the association between childhood diet and cardiovascular mortality. Design: Historical cohort study. Setting: 16 centres in England and Scotland. Participants: 4028 people (from 1234 families) who took part in Boyd Orr’s survey of family diet and health in Britain between 1937 and 1939 followed up through the National Health Service central register. Exposures studied: Childhood intake of fruit, vegetables, fish, oily fish, total fat, saturated fat, carotene, vitamin C, and vitamin E estimated from household dietary intake. Main outcome measures: Deaths from all causes and deaths attributed to coronary heart disease and stroke. Results: Higher childhood intake of vegetables was associated with lower risk of stroke. After controlling for age, sex, energy intake, and a range of socioeconomic and other confounders the rate ratio between the highest and lowest quartiles of intake was 0.40 (95% confidence interval 0.19 to 0.83, p for trend 0.01). Higher intake of fish was associated with higher risk of stroke. The fully adjusted rate ratio between the highest and lowest quartile of fish intake was 2.01 (95% confidence interval 1.09 to 3.69, p for trend 0.01). Intake of any of the foods and constituents considered was not associated with coronary mortality. Conclusions: Aspects of childhood diet, but not antioxidant intake, may affect adult cardiovascular risk.

Endothelial dysfunction in childhood infection.

Background—Atherosclerosis begins in early life, and endothelial dysfunction is recognized as a key initiating event in the development of atherosclerosis. Although infection has been implicated in endothelial dysfunction and atherogenesis, the impact of acute common childhood infections on the vascular endothelium is unknown. Methods and Results—We studied 600 children aged 10 years drawn from the Avon Longitudinal Study of Parents and Children. The children were divided into 3 groups: those with current acute infection (AI; n=135; 73 boys and 62 girls); a convalescent group with infection in the past 2 weeks (n=166; 78 boys and 88 girls), and a healthy control group (n=299; 131 boys and 168 girls). Endothelial function was determined in all subjects by high-resolution ultrasound to measure brachial artery flow-mediated dilation (FMD) and was expressed as the percentage change in diameter from baseline after reactive hyperemia. FMD was repeated in 40 children in the AI group and 50 in the control group after a mean interval of 1 year. FMD was lower in both the AI group (6.3±2.7%, mean±SD) and the convalescent group (8.1±3.1%) than in the control group (9.7±2.5%; P<0.001 for both). The observed differences in FMD remained after adjustment for potential confounding variables. At the repeat visit, FMD was unchanged in controls (P=0.85) but improved in the AI group (P<0.001). Conclusions—Acute infection in childhood is associated with impaired endothelium-dependent vasodilation. These findings support a potential role for previously unsuspected extrinsic inflammatory stimuli in the pathogenesis of early atherosclerosis.

Physical Activity and Blood Pressure in Childhood. Findings From a Population-Based Study

The pathological processes associated with development of cardiovascular disease begin early in life. For example, elevated blood pressure (BP) can be seen in childhood and tracks into adulthood. The relationship between physical activity (PA) and BP in adults is well-established, but findings in children have been inconsistent, with few studies measuring PA mechanically. Children aged 11 to 12 years were recruited from the Avon Longitudinal Study of Parents and Children. 5505 had systolic and diastolic BP measurements, plus valid (at least 10 hours for at least 3 days) accelerometer measures of PA; total PA recorded as average counts per minute (cpm) over the period of valid recording, and minutes per day spent in moderate to vigorous PA (MVPA). Data on a number of possible confounders were also available. Small inverse associations were observed; for systolic BP, &bgr;=−0.44 (95% confidence interval −0.59, −0.28) mm Hg per 100 cpm, and &bgr;=−0.66 (95% CI −0.92, −0.39) mm Hg per 15 minutes/d MVPA, adjusting for child’s age and gender. After adjustment for potential confounders, associations were weakened but remained. When PA variables were modeled together, associations with total PA were only a little weaker, whereas those with MVPA were substantially reduced; for systolic BP, &bgr;=−0.42 (95% CI −0.71, −0.13) mm Hg per 100 cpm, and &bgr;=−0.03 (95% CI −0.54, 0.48) mm Hg per 15 minutes/d MVPA. In conclusion, higher levels of PA were associated with lower BP, and results suggested that the volume of activity may be more important than the intensity.