Study population and design
This study was part of the Amsterdam Born Children and their Development (ABCD)-study, a prospective cohort study based in the Netherlands. The ABCD-study aims to examine the associations between maternal lifestyle, health and psychosocial circumstances during pregnancy and the child’s health at birth and later in life.(23) Between January 2003 and March 2004, 12,373 pregnant women were approached (>99% of the target population) during their first prenatal visit to an obstetric care provider, of which 8,266 agreed to participate and filled out a pregnancy questionnaire without getting any incentives.
Two weeks after their child’s fifth birthday, mothers who gave permission for follow-up and whose addresses could be retrieved (n= 6,161) received a questionnaire on the health, development and behaviour of their child and an invitation for the child’s health check. The questionnaire was returned for 4,488 children, of which 2,041 participated in the health check consisting of among other, a finger prick for blood collection after an overnight fast, measurements of height, weight, waist circumference and measurements of blood pressure. After the health check children received a small gift. For those children who participated in the health check, mothers were also asked to fill in a validated food frequency questionnaire (FFQ).(24) Information on all ICH components was available from 1,666 children at age 5-6 years. A randomly selected subgroup of 1,081 children were approached for participation in follow-up health measurements at age 11-12 years (March 2015 to June 2016). The health check was similar to the health check at the age of 5, but ultrasound measurements of CIMT were added. For participation children received a gift voucher worth of 10 euros. From this group, 607 children participated at both time points and 559 children had information on the cardiovascular profile. Information from these 559 children were used to investigate the association between ICH at age 5-6 and cardiovascular health at age 11-12. The information of 459 children could be used for the association between ICH at age 5-6 and CIMT. Flowchart of the study population is presented in figure 1.
For inclusion in stage 1 of the current study the children had to meet the following criteria: 1) availability of information on maternal smoking status during pregnancy, 2) participating in the five year health check with cardiovascular measurements, 3) filled out FFQ, 4) filled out questionnaire on physical activity, sedentary behaviour and sleep duration. For inclusion in stage 2 of the study, children had to participate in the eleven year health check with cardiovascular measurements. Exclusion criteria’s from participating in the study were: non-fasting blood samples, congenital heart malformations or use of medication altering blood pressure or lipid concentrations.
Ethnicity was based on the mother and her mother`s country of birth, derived from the pregnancy questionnaire and categorized into Dutch, Turkey, Moroccan and Surinamese (the three most common non-Western ethnicities in the Netherlands). The remaining ethnicities were categorized into western and non-western ethnicities. Information on mother’s and father’s weight and height to calculate parent’s body mass index (BMI) was derived from the questionnaire mother’s received after their child’s fifth birthday. Information on socioeconomic status (maternal education level) and cardiovascular diseases in the immediate family was also derived from this questionnaire. Maternal educational level was divided into low (primary school, technical secondary education, lower vocational secondary education), moderate (degree higher vocational secondary education, academic secondary education, intermediate vocational education) or high (degree higher vocational education, university). Cardiovascular diseases in the immediate family were answered by marking ‘no’, ‘yes’ or ‘don’t know’ for the following diseases by the mother, the child’s biological father and their first degree relatives: overweight, hypertension <55 years, high cholesterol, stroke < 55 years, heart attack < 55 years and dead from heart attack < 55 years.(25) Information on the child’s sexual maturation at the age of 11-12 was assessed by the Tanner scale, scored by the mother.(26)
Considered health behaviours were weight status, physical activity, diet, screen time, sleep duration and prenatal smoke exposure, apart from weight status all reported by the mother. Weight and height were measured once to calculate BMI (weight in kg/height in cm2). Weight was measured to the nearest 100g by using a Marsden weighing scale (model MS-4102, Oxfordshire, UK) and height to the nearest mm with a Leicester portable height measure (Seca, Hamburg, Germany). The health check was administered at both time points by trained student assistants, trained PhD-candidates and research staff of the ABCD-study. At age 5-6 years the measurements took place at the child’s primary school except for those children enrolled in small schools, children who moved outside Amsterdam and the 11-12-year-old children. For these children, the health check took place at a central location during the weekend and holidays. For defining metabolic syndrome, waist circumference was measured placing a Seca measuring tape around the abdomen between the costal border and iliac crest. Children aged 5-6 wore underwear only, children at age 11-12 wore sport outfits. Information on physical activity included both recreational and organized physical activity outside school hours as well as transport to and from school cycling. Hours of recreational physical activity was assessed by asking the hours of playing outside at schooldays and in weekends for both summer and winter. The total hours of organized sport activities per week and the total hours of cycling to and from school were added to a total physical activity score.(27)
The FFQ that was used to evaluate the children’s food consumption consisted of questions regarding the 71 most consumed food items by Dutch children.(23) For the present study, we included information regarding fruits and vegetable intake, fish intake, fibre intake and intake of sugar-sweetened beverages in line with the healthy diet definition of the AHA.(4) The AHA guideline looks at the intake of fibre-rich whole grains, while the FFQ used in this present study measures total intake. Fibre intake was considered sufficient if it accounted 3g/MJ, recommended by the Health council of the Netherlands.(28) Sodium intake could not be assessed with our FFQ. For other components besides fibre and sodium, the AHA cut-offs for a healthy diet were used: ≥450 g of fruits and vegetables/day, ≥2 servings of fish/week with a total weight of ≥200 g and ≤450 kcal of sugar-sweetened beverages/week based on a 2000kcal diet. A comparison of our definition with the AHA definition can be found in supplementary table 2.
For the assessment of screen time, the number of hours per day children were watching TV, DVD or VIDEO and how many hours they played games on computer, XBOX or other types of videogames were asked. Hours of screen time for both schooldays and weekends were ranked in six categories from ‘(almost) never’ to ‘five or more hours per day’.(29) Information on children’s sleep duration included the total hours of sleep per day, separately for schooldays and in the weekends. The average hours of sleep per day was calculated by multiplying the hours of sleep on schooldays by five and the hours of sleep in the weekend by two and then adding these two numbers together, divided by seven. For all the above stated behaviours, a weighted weekly average was calculated . Mother’s smoking habits during pregnancy were assessed from the pregnancy-questionnaire in which mothers scored the number of cigarettes smoked daily.
At age 5-6, plasma glucose, serum lipids and triglyceride concentrations were determined in capillary blood, collected after an overnight fast by a finger puncture by using a validated kit, developed for ambulatory purposes (Demecal: LabAnywhere, Haarlem, The Netherlands).(30) At age 11-12, capillary blood was collected by finger puncture after 3 hours fasting and analysed by the point-of-care analyser Alere Cholestech LDX machine using Lipid Profile and GLU cassettes (Cholestech Alere Health Hayward, CA, USA).(31) At both time points, blood pressure was measured by the Omron 705 IT (Omron Health Inc, Bannockburn, IL, USA)(32) in sitting position with the arm supported at the heart level. After a test reading and fifteen minutes of rest, blood pressure was measured twice on the upper right arm with an appropriate cuff. If these measurements differed >10mmHg, a third measurement was performed.(33) The systolic and diastolic blood pressure were determined by averaging the two closest measurement. The research location and research staff were similar to those reported by the calculation of weight and height.
Defining ICH at age 5-6 years
On each ICH component, children could score ‘ideal’ (score=1) or ‘non-ideal’ (score=0). To define ICH components as ideal, the AHA recommendation was used for the following components: BMI <85th percentile according to the WHO growth reference(34) ideal diet when three out of four components were met,(4) fasting plasma glucose <5.6 mmol/L, total cholesterol <4.40 mmol/L and blood pressure <90th percentile based on reference values from the guideline of the American Academy of Pediatrics(35). Physical activity was considered ideal according to the AHA when children were physically active at moderate or vigorous intensity for at least 60 minutes per day. In our study the children of mother’s who reported a total physical activity score of ≥7 hours per week were considered ideal.(9)
For the extended ICH score, a score on three additional health behaviours were added. There is no evidence-based cut-off for screen time. Based on a commonly used cut-off, we considered ≤2 hours of screen time per day as ideal.(29) Sleep duration was considered ideal if children slept ≥10 hours per night as recommended by the National Sleep Foundation.(36) Children from mothers who reported not having smoked during pregnancy received an ideal smoking score. The definition of each component according to AHA and the additions are listed in supplementary table 2.
The score on extended ICH ranged from zero to nine; zero to five points was considered poor, six and seven points intermediate and eight or nine points good ICH. This subdivision was made to create roughly equal groups in size, to compare groups with relatively poor, intermediate and good cardiovascular health..
Carotid intima-media thickness
Ultrasound measurements of the common carotid artery (CCA) were performed with the automated Panasonic Cardio Health Station V1.8 (Diagnostic Ultrasound System GM-72P00A) by three experienced ultrasound technicians at the central locations where the health check took place. During this measurement, children were in lying position with their head at a 45 degree angle. CIMT was measured bilaterally at angles 150, 120 and 90 on the right CCA and at 210, 240 and 270 on the left CCA. The software automatically identified the region of interest and froze the image. Mean CIMT was calculated by averaging the measured angles, with a minimum of at least three angles. Out of 559 individuals, 459 individuals had a CIMT measurement with at least three angles, whereof 442 individuals had all six angles measured. Increased risk CIMT was defined as a CIMT of ≥90th percentile of the cohort.
Secondary outcomes were glucose, total cholesterol, high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), systolic and diastolic blood pressure and BMI at the age of 11-12 (all continuous). The following outcome variables were dichotomized: low HDL-C (<10th percentile), high TG (≥75th percentile), (pre) hypertension (systolic and/or diastolic blood pressure ≥90th percentile) and overweight (BMI ≥85th percentile). Participants were considered having metabolic syndrome when they met three or more of the following criteria: waist circumference ≥75th percentile, (pre) hypertension, low HDL-C, high TG and glucose ≥75th percentile.(37) All percentiles in this paragraph are based on data of the own cohort.
We investigated the representativeness of the included subgroup by comparing the baseline characteristics between the non-included group (i.e. those who were approached at age 5-6, but did not participate in the questionnaire and/or health check at age 5-6) and the included group (i.e. those who participated both in the questionnaire and health check at age 5-6) by an independent samples t-test for continuous variables and the χ2 test for categorical variables.
Stage 1 - Differences in demographic characteristics between the poor, intermediate and good ICH groups (based on extended ICH score) were tested by one-way analysis of variance (ANOVA) for continuous variables and the χ2 test for the categorical variables. The association of individual health behaviours, health factors and lipids with the extended ICH score at age 5-6 was evaluated by means of sex- and age adjusted multivariable linear regression models. P-for-trend was calculated considering ICH as a continuous variable.
Stage 2 - We studied the association between the extended ICH score at age 5-6 with CIMT and cardiometabolic outcomes at age 11-12 by means of multivariable linear regression models for continuous outcomes and multivariable logistic regression models for dichotomous outcomes. We considered the ICH variable as a continuous variable to calculate p-for-trend. For these analyses, all models included age, sex and maturation. To examine whether the association with respect to the dichotomous outcomes was present in children with a healthy weight at baseline, we repeated the logistic regression analysis excluding children with overweight at age 5-6.
All analyses were repeated with the original ICH score.
IBM SPSS Statistic software version 20.0 (IBM Corp, Armonk, NY, USA) was used for the analysis. A p-value of <0.05 was considered statistically significant.