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EYHS database

Content of the EYHS database – click here 

Methods used in EYHS

Testing was conducted throughout the majority of the school year to
account for seasonal effects on the assessed parameters, and daily
order of testing was standardized to minimize between-test
interaction. Many of the tests and protocols utilized in the EYHS are
standard procedures and have been well validated for children of this
age. Where this is not the case, validation studies were performed.
The EYHS design minimizes testing error within the constraints of
finance, human and physical resources, and testing time available.
Physical Measures. Height and weight were assessed by standard
anthropometric procedures. Pubertal status was assessed according to
Tanner stages. Pubertal stage was assessed by a researcher of the
same gender as the child, using brief observation. In both age and
gender groups, pubertal stage was identified using a 5-point scale of
pictures — girls according to breast development and pubic hair
growth and boys according to genital development and pubic hair
growth.
Skinfold thicknesses were measured with Harpenden fat calipers at the
biceps, triceps, subscapular, suprailiac, and medial calf sites. Two
measurements were taken at each position, and if the difference
between the two measurements was more than 2 mm, a third
measurement was taken. The mean value of the two closest
measurements was used for analysis. Waist circumference was
measured twice with a metal anthropometric tape midway between the
lower rib margin and the iliac crest, at the end of gentle expiration. Hip
circumference was measured twice with a metal anthropometric tape
at the level of the great trochanter (not lower than symphysis level).
The mean value of the two measurements was used for analysis.
Blood Pressure. Resting systolic and diastolic blood pressure were
measured in the sitting position using the child’s left arm, with a
Dinamap adult/pediatric and neonatal vital signs monitor (model XL,
Critikron, Inc., Tampa, FL). Measurements were taken using a
standard pressure cuff of the correct size. The children were
introduced to the monitor and allowed to sit quietly by themselves for
at least 5 min prior to measurement. Five measurements were then
taken at 2-min intervals. The mean of the last three measurements
was used for analysis.
Blood Sampling and Analysis. Fasting (overnight) intravenous blood
samples were taken at the start of the day from the antecubital vein,
application of an anesthetic cream (lidocaine/prilocaine; EMLA cream,
AstraZeneca). Breakfast was provided immediately after blood
sampling. Blood samples were aliquoted and separated within 30 min
of venipuncture and samples were stored at –80°C until transported to
a WHO-certified laboratory for analysis.
Total cholesterol, high density lipoprotein cholesterol (HDL-C), and
triglyceride (TG) were measured by enzymatic methods. Glucose was
analyzed by the hexokinase method. Each of these was measured on
an Olympus autoanalyser (model AU600, Olympus Diagnostica GmbH,
Hamburg, Germany). Insulin was measured by enzyme immunoassay
(microtitre plate format; Dako Diagnostics Ltd., Ely, England). The
HDL-C:TC ratio was subsequently calculated, and low-density
lipoprotein cholesterol (LDL-C) was calculated using the Friedwald
equation.11 Spun white blood cells were stored at –80C for DNA
extraction.
Food Intake. Dietary intake was assessed using a 24-h recall face-toface
interview supported by a parent-assisted food record. This
method provides valid estimates of children’s food intake for the
purpose of group comparison.12 The advantages of the 24-h recall are
that the burden on the child to complete the food-intake interview is
relatively minor, and that reading or writing skills are not required.
Disadvantages are that the subject could have difficulty remembering
what and how much they ate during the last 24-h, and that a single
recall represents only a snapshot of a child’s usual intake as the result
of day-to-day variations. This method has been found, however, to be
a suitable instrument for cross-sectional measures of dietary intake
among children from the age of 8 y.13
To aid in estimating food amounts during the interview, different-sized
drinking glasses, plates, spoons, etc. were shown to the children
together with pictures of different portion sizes of the most common
foods and food groups. The interview lasted 20 to 30 min, and the
quality of each interview was rated on a scale of 1 (very satisfactory)
to 5 (very unsatisfactory) by the interviewer. Interviews rated 4 or 5
were noted for potential future exclusion from analyses.
Physical Activity. The MTI accelerometer (model 7164; former
Computer Science Applications) was chosen for use in this study. The
MTI accelerometer is an electronic motion sensor comprising a single
plane (vertical) accelerometer. The monitors are small (4.5 × 3.5 ×
1.0 cm) and light (about 43 g) and are worn in an elastic belt around
the waist. Verbal and written instructions were given to both the
children and their parents regarding its use. All children were
instructed to wear the monitor continuously during the day, except
when doing water-based activities. The activity counts detected by the
accelerometer were averaged and stored every 60 or 20 s for at least
4 consecutive days. After receiving accelerometers back from children
the collected data were downloaded to a computer and derivative
variables were calculated using customized software. Over 100
derivative variables were calculated comprising measures of all
relevant dimensions of children’s activity.
The MTI accelerometer has been validated in both children and
adolescents using heart rate telemetry, indirect calorimetry,
observational techniques, and doubly labeled water. In the latter
study, accelerometer counts were significantly related to energy
expenditure as measured by total energy expenditure (r = 0.39, P <
0.05), activity energy expenditure (r = 0.54, P < 0.01), and physical
activity level (r = 0.58, P < 0.01). Furthermore, in a mechanical
setting, the MTI accelerometer demonstrates good intra-instrument
reliability (coefficient of variation 4.4%) and reasonable interinstrument
reliability (coefficient of variation 5%) within the “normal”
range of human locomotion.
Cardiorespiratory Fitness. Cardiorespiratory fitness, defined as
maximal power output per kilogram of body weight, was measured
using a graded maximal exercise test on an electronically braked cycle
ergometer (Monark Ergomedic 839, Vansbro, Sweden), according to a
previously reported protocol.
Two test protocols were used: a) for 9 year-olds, initial and
incremental workloads were 20 W for children weighing less than 30
kg and 25 W for those weighing 30 kg or more; and b) for 15 yearolds,
initial and incremental workloads were 40 W for girls and 50 W
for boys.
Workload was programmed to increase after every 3 min. Heart rate
(HR) was recorded continuously (Polar Vantage, Kempele, Finland)
throughout the test, and the test continued until the subject was no
longer able to continue. Criteria for a maximal effort were a) HR P185
or b) subjective observation from the researcher that the child could
not continue (after vocal encouragement if necessary). If the child’s
pedaling rate dropped below 30 rpm, the child was considered to have
stopped the test. The cycle ergometer was electronically calibrated
once every test day and mechanically calibrated after being moved
between schools.
Self-reported Variables. A computer-based child’s questionnaire was
used to gather information about children’s smoking habits, alcohol
intake, diet preferences, and various types of physical activity.
Questions addressing psychosocial and environmental factors that
influence children’s physical activity were also asked. A computerbased
questionnaire is feasible in this study because of the small
number of children tested daily (n < 10).
A separate questionnaire was completed by the parents, based on the
questionnaire used in the Northern Ireland Childhood Coronary
Prevention Study. Data collected separately from both parents
included demographic data, self-reported health status, family income,
level of education, ethnicity, level of CVD risk, family history of CVD,
the child’s birth weight, and breast-feeding practices. Socioeconomic
position was assessed using parental education, occupation, and family
income data.
Both questionnaires were translated into the relevant languages and
back-translated to ensure accuracy. Discussions with researchers from
each country ensured that the true meanings of questions were notlost during the process.