Preventing Childhood Obesity - Evidence Policy and Practice.pdf

Monitoring of childhood obesity
Nooyens et al recently showed that older people do
have lower mean BMI compared to middle - aged
people but, when followed prospectively, also, older
people gain weight. 17 This example is taken from data
in adults but clearly, age - period - cohort effects are also
present in children and adolescents.
There are many methodological pitfalls to consider
in the interpretation of secular trends in overweight
and obesity, as well as risk factors and disease incidence.
The associations between these trends usually
depend on the strengths of the association between
obesity and a particular disease, and the time lag
between the onset of obesity and the incidence of
disease. For instance, the rise in the prevalence of type
2 diabetes is usually related to an increase in the prevalence
of obesity because of the strength of the association
between the two. 18 Time trends in obesity, on the
other hand, may not be related to trends in the incidence
of cardiovascular disease 19,20 or cancer. 21 This is
because of the relatively low risk associated with
obesity, the importance of many other risk factors for
these diseases that may be unrelated to changes in
obesity and the long lag - time between obesity and the
incidence of cardiovascular disease endpoints and different
types of cancer. This means, for instance, that
there is a decreasing secular trend observed in cardiovascular
risk factors and the incidence of cardiovascular
disease when at the same time there is an increase
in the prevalence of obesity. 19,20 This is despite the fact
that, on an individual basis, there is a significant association
between measures of overweight such as BMI
and cardiovascular risk. 19,20
As population characteristics change over time,
these changes may have an influence on relative risk
estimates of obesity for diseases, such as cancer, for
other exposures because of effect - measure modification.
The impact of population changes on comparability
between epidemiologic studies can be kept to a
minimum if investigators assess obesity - disease associations
within strata of other exposures, and present
results in a manner that allows comparisons across
studies. Effect - measure modification is an important
component of data analysis that is needed to obtain a
complete understanding of disease etiology. 22
Monitoring determinants and consequences of
obesity can, therefore, lead to interesting hypotheses
about potential explanations of associations but
are usually weak in their level of evidence for causal
relationships. These methodological problems also
hamper the evaluation of effectiveness of policy interventions
on obesity and health.
Screening — m easuring c hildren for
o besity c ase finding
When heights and weights are routinely monitored,
there is will be individuals who meet the criteria for
overweight or obesity. If the data are subsequently
reported to the children and/or their parents, or are
followed by referral to interventions, this would bring
monitoring into the realms of screening. In essence, it
would be screening for individuals who may benefit
from interventions aimed at weight gain prevention
or weight management, even though the primary
purpose of the measurement may have been for monitoring
population trends
Following the original criteria for screening by
Wilson and Jungner 23 and published by WHO in
1968, there have been more extensive lists of criteria
for the viability, effectiveness and appropriateness of
a screening programme (see below) (Table 21.1 ).
Screening for obesity in different medical settings
has been evaluated. Wilson and McAlpine have
reviewed this for primary care. 25 Whitlock et al 26 and
Westwood et al 27 have reviewed the usefulness of
screening in children. In all three reviews it is argued
that screening is compromised by the fact that there
is little generalizable evidence for the effectiveness of
primary care interventions in unselected patients.
Although there is not much scientific literature on
this, there are indications that the consequences of
routinely assessed weight and height in individuals in
surveys may lead to differences in participation rates.
If it is known in advance that routinely measured
weights and heights measured at children in school are
followed by a referral to an intervention requiring the
participation of parents and children this may lead to
a lower likelihood that parents of children who are
overweight or obese and who are not interested in an
intervention will give their permission for their child
to be measured.
There are ethical questions surrounding the feedback
of information obtained by screening. The issue
is whether or not parents or (in the case of adolescents)
the children themselves have a right to access
the measurements taken and their interpretation. In
The UK National Child Measurement Programme
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