Publications by authors named "Peter L Kristensen"

17 Publications

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Children's moderate-to-vigorous physical activity on weekdays versus weekend days: a multi-country analysis.

Int J Behav Nutr Phys Act 2021 02 10;18(1):28. Epub 2021 Feb 10.

MRC Epidemiology Unit & Centre for Diet and Activity Research, University of Cambridge, Cambridge, UK.

Purpose: The Structured Days Hypothesis (SDH) posits that children's behaviors associated with obesity - such as physical activity - are more favorable on days that contain more 'structure' (i.e., a pre-planned, segmented, and adult-supervised environment) such as school weekdays, compared to days with less structure, such as weekend days. The purpose of this study was to compare children's moderate-to-vigorous physical activity (MVPA) levels on weekdays versus weekend days using a large, multi-country, accelerometer-measured physical activity dataset.

Methods: Data were received from the International Children's Accelerometer Database (ICAD) July 2019. The ICAD inclusion criteria for a valid day of wear, only non-intervention data (e.g., baseline intervention data), children with at least 1 weekday and 1 weekend day, and ICAD studies with data collected exclusively during school months, were included for analyses. Mixed effects models accounting for the nested nature of the data (i.e., days within children) assessed MVPA minutes per day (min/day MVPA) differences between weekdays and weekend days by region/country, adjusted for age, sex, and total wear time. Separate meta-analytical models explored differences by age and country/region for sex and child weight-status.

Results/findings: Valid data from 15 studies representing 5794 children (61% female, 10.7 ± 2.1 yrs., 24% with overweight/obesity) and 35,263 days of valid accelerometer data from 5 distinct countries/regions were used. Boys and girls accumulated 12.6 min/day (95% CI: 9.0, 16.2) and 9.4 min/day (95% CI: 7.2, 11.6) more MVPA on weekdays versus weekend days, respectively. Children from mainland Europe had the largest differences (17.1 min/day more MVPA on weekdays versus weekend days, 95% CI: 15.3, 19.0) compared to the other countries/regions. Children who were classified as overweight/obese or normal weight/underweight accumulated 9.5 min/day (95% CI: 6.9, 12.2) and 10.9 min/day (95% CI: 8.3, 13.5) of additional MVPA on weekdays versus weekend days, respectively.

Conclusions: Children from multiple countries/regions accumulated significantly more MVPA on weekdays versus weekend days during school months. This finding aligns with the SDH and warrants future intervention studies to prioritize less-structured days, such as weekend days, and to consider providing opportunities for all children to access additional opportunities to be active.
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http://dx.doi.org/10.1186/s12966-021-01095-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877033PMC
February 2021

Hyperinsulinaemic-hypoglycaemic glucose clamps in human research: a systematic review of the literature.

Diabetologia 2021 Apr 10;64(4):727-736. Epub 2021 Feb 10.

Department of Endocrinology and Nephrology, Nordsjællands Hospital, Hillerød, Denmark.

Aims/hypothesis: The hyperinsulinaemic-hypoglycaemic glucose clamp technique has been developed and applied to assess effects of and responses to hypoglycaemia under standardised conditions. However, the degree to which the methodology of clamp studies is standardised is unclear. This systematic review examines how hyperinsulinaemic-hypoglycaemic clamps have been performed and elucidates potential important differences.

Methods: A literature search in PubMed and EMBASE was conducted. Articles in English published between 1980 and 2018, involving adults with or without diabetes, were included.

Results: A total of 383 articles were included. There was considerable variation in essential methodology of the hypoglycaemic clamp procedures, including the insulin dose used (49-fold difference between the lowest and the highest rate), the number of hypoglycaemic steps (range 1-6), the hypoglycaemic nadirs (range 2.0-4.3 mmol/l) and the duration (ranging from 5 to 660 min). Twenty-seven per cent of the articles reported whole blood glucose levels, most venous levels. In 70.8% of the studies, a dorsal hand vein was used for blood sampling, with some form of hand warming to arterialise venous blood in 78.8% of these. Key information was missing in 61.9% of the articles.

Conclusions/interpretation: Although the hyperinsulinaemic-hypoglycaemic clamp procedure is considered the gold standard to study experimental hypoglycaemia, a uniform standard with key elements on how to perform these experiments is lacking. Methodological differences should be considered when comparing results between hypoglycaemic clamp studies.

Prospero Registration: This systematic review is registered in PROSPERO (CRD42019120083).
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http://dx.doi.org/10.1007/s00125-020-05361-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7940281PMC
April 2021

The potential for improvement of outcomes by personalized insulin treatment of type 1 diabetes as assessed by analysis of single-patient data from a randomized controlled cross-over insulin trial.

Diabetes Res Clin Pract 2017 Jan 16;123:143-148. Epub 2016 Nov 16.

Department of Clinical Research, Nordsjællands University Hospital, Hillerød, Denmark; Steno Diabetes Center, Gentofte, Denmark; Faculties of Health Sciences, University of Aarhus, Denmark.

Aims: The evidence for optimal insulin treatment in type 1 diabetes is mainly based on randomised controlled trials applying a parallel-group design. Such trials yield robust general results but crucial individual treatment effects cannot be extracted. We aimed to assess the potential for further improvement of outcomes by personalized insulin therapy by analyzing data from a cross-over trial at individual level.

Methods: Post hoc analysis of data from a two-year multicentre, prospective, randomised, open, blinded endpoint (PROBE) trial (the HypoAna trial). In a cross-over design 114 patients with type 1 diabetes and recurrent severe hypoglycemia were treated with basal-bolus therapy based on analog (detemir/aspart) or human (NPH/regular) insulin aiming at maintenance of baseline HbA1c levels. For each patient a superior outcome was defined as fewer events of severe hypoglycemia defined by need for third party treatment assistance or a more than 0.4% (4.4mmol/mol) lower HbA1c.

Results: Only one quarter had comparable outcome of the two treatments in terms of rate of severe hypoglycemia or HbA1c. Twice as many patients had superior outcome of analog-based as compared to human insulin-based insulin treatment. The rate of severe hypoglycemia with the superior treatment was lower compared to the rates obtained with analog insulin and with human insulin (0.67, 1.09, and 1.57 episode per patient-year, respectively (p<0.0001)).

Conclusions: Personalized insulin treatment of type 1 diabetes based on single-patient evidence may improve outcomes significantly compared to a general treatment approach.
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http://dx.doi.org/10.1016/j.diabres.2016.11.003DOI Listing
January 2017

Impact of the TCF7L2 genotype on risk of hypoglycaemia and glucagon secretion during hypoglycaemia.

Endocr Connect 2016 Nov 10;5(6):53-60. Epub 2016 Oct 10.

Department of CardiologyNephrology and Endocrinology, Nordsjællands Hospital, Hillerød, Denmark.

Introduction: In healthy carriers of the T allele of the transcription factor 7-like 2 (TCF7L2), fasting plasma glucagon concentrations are lower compared with those with the C allele. We hypothesised that presence of the T allele is associated with a diminished glucagon response during hypoglycaemia and a higher frequency of severe hypoglycaemia (SH) in type 1 diabetes (T1DM).

Material And Methods: This is a post hoc study of an earlier prospective observational study of SH and four mechanistic studies of physiological responses to hypoglycaemia. 269 patients with T1DM were followed in a one-year observational study. A log-linear negative binomial model was applied with events of SH as dependent variable and TCF7L2 alleles as explanatory variable. In four experimental studies including 65 people, TCF7L2 genotyping was done and plasma glucagon concentration during experimental hypoglycaemia was determined.

Results: Incidences of SH were TT 0.54, TC 0.98 and CC 1.01 episodes per patient-year with no significant difference between groups. During experimental hypoglycaemia, the TCF7L2 polymorphism did not influence glucagon secretion.

Discussion: Patients with T1DM carrying the T allele of the TCF7L2 polymorphism do not exhibit diminished glucagon response during hypoglycaemia and are not at increased risk of severe hypoglycaemia compared with carriers of the C allele.
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http://dx.doi.org/10.1530/EC-16-0050DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5097143PMC
November 2016

A Longitudinal Study of Objectively Measured Built Environment as Determinant of Physical Activity in Young Adults: The European Youth Heart Study.

J Phys Act Health 2015 Jul 22;12(7):909-14. Epub 2014 Aug 22.

Dept of Sport Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.

Background: This longitudinal study aimed to examine if a Movability Index (MI), based on objectively measured built environment characteristics, was a determinant for objectively measured physical activity (PA) among young adults.

Methods: Data collected from 177 persons participating in the Danish part of the European Youth Hearth Study (EYHS) was used to examine the effect of the built environment on PA. A MI was developed using objectively measured built environment characteristics, and included residential density, recreational facilities, daily destinations and street connectivity.

Results: Results showed a positive cross-sectional association between MI and PA. PA decreased from baseline to follow-up. MI increased, primarily due to participants relocating to larger cities. An increase in MI from baseline to follow-up was associated with a reduced decrease in PA for females.

Conclusions: Our findings suggest that the built environment is a determinant for PA, especially for females. The found gender differences might suggest the need to develop gender specific environmental indices in future studies. The validity of the measures can be further improved by creating domain specific PA measures as well as domain specific environmental indices and this can potentially reveal more specific built environment determinants for PA.
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http://dx.doi.org/10.1123/jpah.2014-0039DOI Listing
July 2015

Glucose-dependent insulinotropic polypeptide augments glucagon responses to hypoglycemia in type 1 diabetes.

Diabetes 2015 Jan 22;64(1):72-8. Epub 2014 Jul 22.

Center for Diabetes Research, Department of Medicine, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.

Glucose-dependent insulinotropic polypeptide (GIP) is glucagonotropic, and glucagon-like peptide-1 (GLP-1) is glucagonostatic. We studied the effects of GIP and GLP-1 on glucagon responses to insulin-induced hypoglycemia in patients with type 1 diabetes mellitus (T1DM). Ten male subjects with T1DM (C-peptide negative, age [mean ± SEM] 26 ± 1 years, BMI 24 ± 0.5 kg/m(2), HbA1c 7.3 ± 0.2%) were studied in a randomized, double-blinded, crossover study, with 2-h intravenous administration of saline, GIP, or GLP-1. The first hour, plasma glucose was lowered by insulin infusion, and the second hour constituted a "recovery phase." During the recovery phase, GIP infusions elicited larger glucagon responses (164 ± 50 [GIP] vs. 23 ± 25 [GLP-1] vs. 17 ± 46 [saline] min ⋅ pmol/L, P < 0.03) and endogenous glucose production was higher with GIP and lower with GLP-1 compared with saline (P < 0.02). On the GIP days, significantly less exogenous glucose was needed to keep plasma glucose above 2 mmol/L (155 ± 36 [GIP] vs. 232 ± 40 [GLP-1] vs. 212 ± 56 [saline] mg ⋅ kg(-1), P < 0.05). Levels of insulin, cortisol, growth hormone, and noradrenaline, as well as hypoglycemic symptoms and cognitive function, were similar on all days. Our results suggest that during hypoglycemia in patients with T1DM, exogenous GIP increases glucagon responses during the recovery phase after hypoglycemia and reduces the need for glucose administration.
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http://dx.doi.org/10.2337/db14-0440DOI Listing
January 2015

Intervention effects on adolescent physical activity in the multicomponent SPACE study: a cluster randomized controlled trial.

PLoS One 2014 12;9(6):e99369. Epub 2014 Jun 12.

Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark; Centre for Intervention Research in Health Promotion and Disease Prevention, National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Background: Multicomponent school-based interventions have the potential to reduce the age-related decline in adolescents' physical activity (PA), yet there is not consistent evidence to guide non-curricular and school environment interventions. The aim of this study was to assess the effectiveness of a multicomponent environmental school-based intervention, designed to reduce the age-related decline in PA among adolescents.

Methods: A cluster randomized controlled trial was conducted with 7 intervention and 7 control schools. Baseline measurements were carried out in spring 2010 with 2 years of follow-up. A total of 1,348 students (11-13 years, in grade 5 and 6) enrolled in the study at baseline. The 14 schools included in the study were located in the Region of Southern Denmark. The intervention consisted of organizational and physical changes in the school environment with a total of 11 intervention components. The primary outcome measure was overall PA (cpm, counts per minute) and was supported by analyses of time spent in MVPA, and time spent sedentary. Furthermore, a secondary outcome measure was PA in school time and during recess. PA was measured using accelerometer (Actigraph GT3X).

Results: A total of 797 students completed the trial and had valid accelerometer data. No significant difference was found for overall PA with an adjusted difference of -19.1 cpm (95% CI: -93, 53) or for school time activity with an adjusted difference of 6 cpm (95% CI: -73, 85). A sensitivity analysis revealed a positive significant intervention effect of PA in recess with an adjusted difference of 95 cpm.

Conclusions: No evidence was found of the overall effect of a non-curricular multicomponent school-based intervention on PA among Danish adolescents. The intervention was positively associated with PA during school time and recess, however, with small estimates. Lack of effect on overall PA could be due to both program theory and different degrees of implementation.

Trial Registration: www.Controlled-Trials.com ISRCTN79122411.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0099369PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4055775PMC
January 2015

The effect of multiple reminders on response patterns in a Danish health survey.

Eur J Public Health 2015 Feb 22;25(1):156-61. Epub 2014 May 22.

1 National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Background: Reminders are routinely applied in surveys to increase response rates and reduce the possibility of bias. This study examines the effect of multiple reminders on the response rate, non-response bias, prevalence estimates and exposure-outcome relations in a national self-administered health survey.

Methods: Data derive from the Danish National Health Survey 2010, in which 298,550 individuals (16 years of age or older) were invited to participate in a cross-sectional survey using a mixed-mode approach (paper and web questionnaires). At least two reminders were sent to non-respondents, and 177,639 individuals completed the questionnaire (59.5%). Response patterns were compared between four groups of individuals (first mailing respondents, second mailing respondents, third mailing respondents and non-respondents).

Results: Multiple reminders led to an increase in response rate from 36.7 to 59.5%; however, the inclusion of second and third mailing respondents did not change the overall characteristics of respondents compared with non-respondents. Furthermore, only small changes in prevalence estimates and exposure-outcome relationships were observed when including second and third mailing respondents compared with only first mailing respondents.

Conclusions: Multiple reminders were an effective way to increase the response rate in a national Danish health survey. However, when differences do exist between respondents and non-respondents, the results suggest that second and third mailings are unlikely to eliminate these differences. Overall, multiple reminders seemed to have only minor effect on response patterns and study conclusions in the present study.
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http://dx.doi.org/10.1093/eurpub/cku057DOI Listing
February 2015

Association between body mass index and caries among children and adolescents.

Community Dent Oral Epidemiol 2014 Feb 14;42(1):53-60. Epub 2013 Jun 14.

National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Objective: The aim of this article was to examine the relationship between childhood caries, body mass index (BMI) and subsequent changes in BMI over 6 years, and to investigate whether these associations were modified by social class.

Methods: Data were from the European Youth Heart Study (EYHS) merged with data on caries experience from the Danish National Board of Health, (SCOR register).

Results: At baseline, 26.2% of the children/adolescents were caries free and 39% at follow-up. A larger percentage of normal weight children/adolescents were caries free, compared with the overweight/obese group of children/adolescents. The linear regression analysis showed that childhood caries was generally not associated with either BMI or subsequent changes in BMI. However, among children whose mothers were well educated, there was an inverse association between caries at baseline and subsequent changes in BMI over a period of 6 years, for example, a high caries experience was associated with a smaller increment in BMI, compared with the group of children with a low caries experience. No association was found for those with lower SES.

Conclusion: An inverse association between caries and subsequent changes in BMI was found, but only among children with well-educated mothers, suggesting that high caries experience may be a marker for low future risk of overweight among the more advantaged. Associations did not appear to be significant among the less advantaged; however, numbers in this group were low, and an association may have been overlooked. Hence, more studies are needed to confirm these findings.
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http://dx.doi.org/10.1111/cdoe.12055DOI Listing
February 2014

Between-school variation in physical activity, aerobic fitness, and organized sports participation: a multi-level analysis.

J Sports Sci 2013 20;31(2):188-95. Epub 2012 Sep 20.

Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.

A large proportion of a child's day is spent at school interacting with certain physical surroundings, teachers, and school friends. Thus, schools could have a marked impact on establishing physical activity habits. The aim of the present study was to assess between-school variation in physical activity, aerobic fitness, and organized sports participation. Altogether, we tested 1766 nine- and fifteen-year-old children attending 242 school classes at 35 different schools in Denmark in 1997-2003. The intra-class correlation coefficient (ICC) for objectively assessed physical activity ranged between 0.06 and 0.18 depending on the dimension of physical activity and the time considered (i.e. school time vs. leisure time). For aerobic fitness, an ICC of 0.10 was observed, whereas that for organized sports participation ranged between 0.01 and 0.10 depending on the age group. Studying between-school variation in physical activity provides information about the extent to which children adjust their physical activity habits according to the social and environmental circumstances that they share, and helps to plan future school-based physical activity studies, especially in terms of sample size and power calculation.
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http://dx.doi.org/10.1080/02640414.2012.723818DOI Listing
July 2013

SPACE for physical activity--a multicomponent intervention study: study design and baseline findings from a cluster randomized controlled trial.

BMC Public Health 2011 Oct 10;11:777. Epub 2011 Oct 10.

Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.

Background: The aim of the School site, Play Spot, Active transport, Club fitness and Environment (SPACE) Study was to develop, document, and assess a comprehensive intervention in local school districts that promote everyday physical activity (PA) among 11-15-year-old adolescents. The study is based on a social ecological framework, and is designed to implement organizational and structural changes in the physical environment.

Methods/design: The SPACE Study used a cluster randomized controlled study design. Twenty-one eligible schools in the Region of Southern Denmark were matched and randomized in seven pairs according to eight matching variables summarized in an audit tool (crow-fly distance from residence to school for 5-6th graders; area household income; area education level; area ethnicity distribution; school district urbanity; condition and characteristics of school outdoor areas; school health policy; and active transport in the local area). Baseline measurements with accelerometers, questionnaires, diaries, and physical fitness tests were obtained in Spring 2010 in 5-6th grade in 7 intervention and 7 control schools, with follow-up measurements to be taken in Spring 2012 in 7-8th grade. The primary outcome measure is objective average daily physical activity and will be supported by analyses of time spent in moderate to vigorous activity and time spent sedentary. Other secondary outcome measures will be obtained, such as, overweight, physical fitness, active commuting to/from school and physical activity in recess periods.

Discussion: A total of 1348 adolescents in 5-6th grade in the Region of Southern Denmark participated at baseline (n = 14 schools). The response rate was high in all type of measurements (72.6-97.4%). There were no significant differences between intervention and control groups at baseline according to selected background variables and outcome measures: gender (p = .54), age (p = .17), BMI (p = .59), waist circumference (p = .17), physical fitness (p = .93), and physical activity (accelerometer) (p = .09). The randomization and matched pair design produced equivalent groups according to central outcome measures and background variables. The SPACE for physical activity Study will provide new insights on the effectiveness of multicomponent interventions to improve adolescents' physical activity level.

Trial Registration: Current Controlled Trials ISRCTN79122411.
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http://dx.doi.org/10.1186/1471-2458-11-777DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202239PMC
October 2011

Television viewing, food preferences, and food habits among children: a prospective epidemiological study.

BMC Public Health 2011 May 13;11:311. Epub 2011 May 13.

Research Unit for Dietary Studies, Institute of Preventive Medicine, Copenhagen University Hospital, Centre for Health and Society, DK-1357 Copenhagen K, Denmark.

Background: Obesity has increased since the early 1980s, and despite numerous attempts, effective strategies to counter this worldwide epidemic are lacking. Food preferences are established early in life and are difficult to change later. There is therefore a need to identify factors that influence the development of food preferences. Our aim was therefore, to investigate cross-sectional and prospective associations between TV viewing habits and food preferences and habits, respectively. We hypothesized that more TV viewing was associated with less healthy concomitant and future food preferences and food habits.

Methods: Data are from the Danish part of European Youth Heart Study (EYHS) I and II, a prospective cohort study conducted among 8-10-year-old and 14-16-year-old Danes in 1997-98. Six years later 2003-04 the 8-10-year-olds were followed up at age 14-16 years, and a new group of 8-10-year olds were included. Data were analysed using mixed linear regression analysis. Cross-sectional analyses included 697 8-10-year-olds and 495 14-16-year-olds. Prospective analyses included 232 pupils with complete data at baseline and follow-up. Associations between TV viewing habits and the sum of healthy food preferences (ΣHFP), and the sum of healthy food habits (ΣHFH), respectively, were examined.

Results: Inverse cross-sectional associations between TV viewing (h/day) and both ΣHFP and ΣHFH were present for both the 8-10-year-old and the 14-16-year-old boys and girls. The frequency of meals in front of the TV (times/week) was also inversely associated with ΣHFP among 8-10-year-old boys, and with ΣHFH in all sex- and age groups. Among girls, baseline TV viewing (h/day) was directly associated with adverse development in the ΣHFP during follow-up. The concomitant 6-year changes in ΣHFH and TV viewing (h/day) were inversely associated in boys.

Conclusions: Long time spent on TV viewing, and possibly to a lesser degree, frequent consumption of meals during TV viewing, seem to be associated with generally having unhealthy food preferences and food habits among school-aged children. These associations, however, were not generally persistent after 6 years of follow-up.
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http://dx.doi.org/10.1186/1471-2458-11-311DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3112126PMC
May 2011

Cardiovascular disease risk factors and blood pressure response during exercise in healthy children and adolescents: the European Youth Heart Study.

J Appl Physiol (1985) 2010 Oct 15;109(4):1125-32. Epub 2010 Jul 15.

Centre for Research in Childhood Health, Institute of Sports Science and Clinical Biomechanics, Univ. of Southern Denmark, Campusvej 55, 5230 Odense, Denmark.

Raised blood pressure (BP) response during exercise independently predicts future hypertension. Subjects with higher BP in childhood also have elevated BP later in life. Therefore, the factors related to the regulation of exercise BP in children needs to be well understood. We hypothesized that physiological cardiovascular disease (CVD) risk factors would influence BP response during exercise in children and adolescents. This is a cross-sectional study of 439 Danish third-grade children and 364 ninth-grade adolescents. Systolic blood pressure (SBP) was measured with sphygmomanometer during a maximal aerobic fitness test. Examined CVD risk factors were high-density lipoprotein (HDL)- and low-density lipoprotein (LDL)-cholesterol, triglyceride, homeostasis model of assessment of insulin resistance (HOMA-IR) score, body mass index (BMI), waist circumference, and aerobic fitness. A random effect model was used to test the hypotheses. In boys, HOMA-IR score and BMI were positively related to SBP response during exercise (β = 1.03, P = 0.001, and β = 0.58, P = 0.017, respectively). The effects sizes of HOMA-IR score and BMI and the significance levels only changed slightly (β = 0.91, P = 0.004, and β = 0.43, P = 0.08, respectively) when the two variables were added in the same model. A significant positive association was observed between aerobic fitness and SBP response in girls (β = 3.13 and P = 0.002). HOMA-IR score and BMI were found to be positively related to the SBP response in male children and youth. At least partly, adiposity and insulin sensitivity seem to influence exercise SBP through different mechanisms. The positive relationship observed between aerobic fitness and SBP response in girls remains unexplainable for us, although post hoc analyses revealed that it was the case in the ninth graders only.
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http://dx.doi.org/10.1152/japplphysiol.00316.2010DOI Listing
October 2010

Six-year change in youth physical activity and effect on fasting insulin and HOMA-IR.

Am J Prev Med 2008 Dec 9;35(6):554-60. Epub 2008 Oct 9.

Department of Exercise, Nutrition and Health Sciences, University of Bristol, Bristol, England.

Background: There is a shortage of longitudinal data analyzing associations between physical activity and indicators of insulin resistance among children and adolescents after accounting for adiposity change. To guide future prevention efforts, data were used from the Danish arm of the European Youth Heart Study to examine these issues.

Methods: Participants were 384 students in Grade 9 (aged 15 years) from the municipality of Odense, Denmark, who participated in surveys in 1997 and 2003. Physical activity was monitored for at least 3 days by accelerometer, and mean counts per minute (CPM) and minutes >3000 CPM per day were obtained. Blood samples were collected, and levels of fasting insulin, fasting glucose, and homeostasis model of assessment of insulin resistance (HOMA-IR) were obtained. Data were analyzed in 2008.

Results: Physical activity declined from 45 minutes >3000 CPM in 1997 to 35 minutes >3000 CPM in 2003. Longitudinal regression analyses showed that a change in minutes >3000 CPM was negatively associated with fasting insulin levels (z=-2.47, p=0.014) and HOMA-IR (z=-2.31, p=0.021) in 2003. Similar findings were found when CPM was used as the physical activity variable. Results demonstrated that a 6-year decline in physical activity was associated with higher insulin and HOMA-IR levels.

Conclusions: The 6-year change in the volume of physical activity engaged in by adolescents aged 15 years was negatively associated with fasting insulin and HOMA-IR. Preventing an age-related decline in physical activity may be an effective means of preventing youth insulin resistance.
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http://dx.doi.org/10.1016/j.amepre.2008.07.007DOI Listing
December 2008

Longitudinal associations of cycling to school with adolescent fitness.

Prev Med 2008 Sep 18;47(3):324-8. Epub 2008 Jun 18.

Exercise, Nutrition and Health Sciences, University of Bristol, UK.

Objective: To investigate whether change in transport to school from non-cycling to cycling was associated with change in cardio-respiratory fitness (CRF) over a six-year follow-up.

Methods: Participants were 384 children (9.7 (0.5) years) who participated in the Danish arm of the European Youth Heart Study in 1997 and who were followed up 6 years later. CRF was assessed by a maximal cycle ergometer test and travel to school was investigated by questionnaire at both time points. Linear regression models were used to investigate associations between CRF and change in mode of travel to school between baseline and follow-up.

Results: Higher CRF was significantly associated with cycling to school in children and adolescents of both sexes. Longitudinal regression models showed that a change in travel mode from non-cycling to cycling was a significant predictor of CRF at follow-up (P<0.001) after adjustment for potential confounders. Participants who did not cycle to school at baseline, but who had changed to cycling at follow-up, were significantly fitter (0.33 W kg(-1)) than those who did not cycle to school at either time point (P=0.001), a difference of 9%.

Conclusion: Cycling to school may contribute to higher cardiovascular fitness in young people.
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http://dx.doi.org/10.1016/j.ypmed.2008.06.009DOI Listing
September 2008

Unit-specific calibration of Actigraph accelerometers in a mechanical setup - is it worth the effort? The effect on random output variation caused by technical inter-instrument variability in the laboratory and in the field.

BMC Med Res Methodol 2008 Apr 11;8:19. Epub 2008 Apr 11.

Institute of Sport Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.

Background: Potentially, unit-specific in-vitro calibration of accelerometers could increase field data quality and study power. However, reduced inter-unit variability would only be important if random instrument variability contributes considerably to the total variation in field data. Therefore, the primary aim of this study was to calculate and apply unit-specific calibration factors in multiple accelerometers in order to examine the impact on random output variation caused by inter-instrument variability.

Methods: Instrument-specific calibration factors were estimated in 25 MTI- and 53 CSA accelerometers in a mechanical setup using four different settings varying in frequencies and/or amplitudes. Calibration effect was analysed by comparing raw and calibrated data after applying unit-specific calibration factors to data obtained during quality checks in a mechanical setup and to data collected during free living conditions.

Results: Calibration reduced inter-instrument variability considerably in the mechanical setup, both in the MTI instruments (raw SDbetween units = 195 counts*min-1 vs. calibrated SDbetween units = 65 counts*min-1) and in the CSA instruments (raw SDbetween units = 343 counts*min-1 vs. calibrated SDbetween units = 67 counts*min-1). However, the effect of applying the derived calibration to children's and adolescents' free living physical activity data did not alter the coefficient of variation (CV) (children: CVraw = 30.2% vs. CVcalibrated = 30.4%, adolescents: CVraw = 36.3% vs. CVcalibrated = 35.7%). High correlations (r = 0.99 & r = 0.98, respectively) were observed between raw and calibrated field data, and the proportion of the total variation caused by the MTI- and CSA monitor was estimated to be only 1.1% and 4.2%, respectively. Compared to the CSA instruments, a significantly increased (9.95%) mean acceleration response was observed post hoc in the batch of MTI instruments, in which a significantly reduced inter-instrumental reliability was observed over time.

Conclusion: The application of unit-specific calibration factors to data collected during free living conditions had no apparent effect on inter-instrument variability. In all probability, the effect of technical calibration was primarily attenuated in the field by other more dominant sources of variation. However, routine technical assessments are still very important for determining the acceleration responses in the batch of instruments being used and, if performed after every field use, for preventing decidedly broken instruments from being returned into the field repeatedly.
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http://dx.doi.org/10.1186/1471-2288-8-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2383921PMC
April 2008

Tracking and prevalence of cardiovascular disease risk factors across socio-economic classes: a longitudinal substudy of the European Youth Heart Study.

BMC Public Health 2006 Jan 27;6:20. Epub 2006 Jan 27.

Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.

Background: The highest prevalence of several cardiovascular disease risk factors including obesity, smoking and low physical activity level is observed in adults of low socioeconomic status. This study investigates whether tracking of body mass index and physical fitness from childhood to adolescence differs between groups of socioeconomic status. Furthermore the study investigates whether social class differences in the prevalence of overweight and low physical fitness exist or develop within the age range from childhood to adolescence.

Methods: In all, 384 school children were followed for a period of six years (from third to ninth grade). Physical fitness was determined by a progressive maximal cycle ergometer test and the classification of overweight was based on body mass index cut-points proposed by the International Obesity Task Force. Socioeconomic status was defined according to The International Standard Classification of Occupation scheme.

Results: Moderate and moderately high tracking was observed for physical fitness and body mass index, respectively. No significant difference in tracking was observed between groups of socioeconomic status. A significant social gradient was observed in both the prevalence of overweight and low physical fitness in the 14-16-year-old adolescents, whereas at the age of 8-10 years, only the prevalence of low physical fitness showed a significant inverse relation to socioeconomic status. The odds of both developing and maintaining risk during the measurement period were estimated as bigger in the group of low socioeconomic status than in the group of high socioeconomic status, although differences were significant only with respect to the odds of developing overweight.

Conclusion: The results indicate that the fundamental possibilities of predicting overweight and low physical fitness at an early point in time are the same for different groups of socio-economic status. Furthermore, the observed development of social inequalities in the absolute prevalence of overweight and low physical fitness underline the need for broad preventive efforts targeting children of low socioeconomic status in early childhood.
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http://dx.doi.org/10.1186/1471-2458-6-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1403767PMC
January 2006