Page 22 - Hello Philippines November 2015 'B' issue

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Lack of exercise ‘highest risk’ for women over 30
“HEART disease warning:
Lack of exercise is worse risk for
over-30s women than smoking or
obesity,” The Independent reports.
It is important to stress that this
headline is based on a result that is
applicable to a population, not to an
individual.
The Australian study the headline
is reporting on looked at population
attributable risk, or PARs. PARs can
be used to estimate the proportion
of cases of a disease, such as heart
disease, that would not occur in a
population if the risk factor, such as
inactivity, was eliminated.
The researchers wanted to
determine the proportion of heart
disease that was attributable to
four specific risk factors: smoking,
physical inactivity, high body mass
index, and high blood pressure.
They looked at groups of women of
different ages.
Two key findings of the study
were that:
• smoking had the greatest PAR
in women under 30 – if women
aged under 30 gave up smoking,
approximately 55-60% of cases of
heart disease would be eliminated
• physical activity had the
greatest PAR in women aged 31
and older – if women aged 31 to
36 increased their physical activity,
about 51% of cases of heart disease
could be eliminated
It pays to emphasise that factors
could have the greatest PAR
simply because they are the most
common, rather than because they
are associated with the greatest
increase in risk for the individual. In
fact, smoking was associated with
the greatest increase in risk of heart
disease at all ages.
It would be unwise to think
you could offset one risk against
another. Just because you take
regular exercise does not mean that
it is safe for you to smoke.
Where did the story come
from? The study was carried out
by researchers from the University
of Sydney and the University of
Queensland in Australia.
Some of the data came from
the Australian Longitudinal Study
on Women’s Health, funded by
the Australian Department of
Health. One of the researchers
was supported by the Australian
National Health and Medical
Research Council.
The study was published in the
peer-reviewed British Journal of
Sports Medicine.
The results of the study were
reported well by BBC News and
The Daily Telegraph. However, the
Daily Mail has misinterpreted the
meaning of the figures reported in
the study – specifically, how the
population attributable risk tool
“works”.
HEALTH and Lifestyle
It reports that individual women
in their thirties who are inactive are
almost 50% more likely to develop
heart disease. However, the study
refers to outcomes at the population
level.
The 50% figure actually refers
to the proportion of heart disease
cases that could be eliminated from
the population as a whole if this
inactivity was not present.
It could be the case that
eliminating a risk factor reduces the
number of cases the most because
it is the most common risk factor in
a population, rather than because
it is associated with the greatest
increase in risk for the individual.
What kind of research was
this? This was an analysis of data
from cohort studies. It aimed to
determine the proportion of heart
disease attributable to four specific
risk factors in Australian women of
different ages.
The figure the researchers were
calculating is called population
attributable risk, or PAR. It indicates much energy is burned off over a
the proportion of cases of a disease
that would not occur in a population
if a risk factor was eliminated. PAR
depends on how common a risk
factor is (its prevalence) and the
strength of its association with the
disease.
Researchers and policy makers
can use these figures to help them
decide which risk factors they
should be targeting to get the
greatest reduction in disease in the
population as a whole.
What did the research involve?
The researchers calculated
population attributable risk for
heart disease that was attributable
to four risk factors:
• high body mass index (BMI)
• smoking
• high blood pressure
• physical inactivity
To do this, they used relative
risks of heart disease associated
with high BMI, smoking, high
blood pressure and physical activity
from the Global Burden of Disease
reports.
The relative risks give a measure
of the strength of the association
between each risk factor and
heart disease. The Global Burden
Smoking was associated with the
greatest increase in risk of heart
disease at all ages. Of the four
factors assessed, smoking had the
highest population attributable risk
in women aged 22 to 27 (59%) and
25 to 30 (56.6%).”
of Disease reported relative risks
based on pooling of results (meta-
analyses) of epidemiological studies.
As the risk associated with risk
factors varies by age and with sex,
the researchers used relative risks
specifically for women and the age
groups they were looking at.
Relative risks in the Global
Burden of Disease reports compared
the risk of heart disease for:
• high BMI (>23kg/m2) versus
low BMI (23kg/m2)
• current smokers versus non-
smokers
• high blood pressure
(>115mmHg average) versus
low blood pressure (<115mmHg
average)
• no, low and moderate physical
activity versus high physical activity was 50.9%.
The latter was assessed using
what is known as MET (metabolic
equivalents), a calculation of how
minute during certain activities. For
example, for most people, running
at 10 mph is equal to 16 METs.
The researchers used estimates
of how common each risk factor was
(prevalence) in Australian women
from the Australian Longitudinal
Study on Women’s Health between
1999 and 2012. This study surveyed
women born from 1973-78 (the
younger cohort), 1946-51 (the mid-
aged cohort), and 1921-26 (the older
cohort) every three years.
The risk factors were defined as:
• high BMI (>23kg/m2)
• current smoking
• high blood pressure (defined
as being diagnosed or treated for
hypertension)
• no or low physical activity
(defined by the Global Burden of
Disease study) – MET minutes per
week were calculated from reported
time spent walking briskly and in
moderate and vigorous leisure time
activities
The researchers used the relative
risks and prevalence estimates to
calculate population attributable
risks using standard methods.
What were the basic results?
The risk of heart disease associated
with each risk factor varied across
age groups, as did the prevalence of
each risk factor.
November 2015 / Fortnightly – No. 22 • UK & Europe Edition
Exercise is important for women of all ages highest population attributable risk
Smoking was associated with the
greatest increase in risk of heart
disease at all ages. Of the four
factors assessed, smoking had the
highest population attributable risk
in women aged 22 to 27 (59%) and
25 to 30 (56.6%).
The population attributable
risk associated with smoking was
lower in women aged 47 to 64 and
in the older cohort, and was 5% in
women aged 73 to 78 (the oldest
group of women with smoking data
available).
In women aged 31 to 90, physical
inactivity (no or low physical
activity) had the highest population
attributable risk of the four
factors assessed. The population
attributable risk of physical
inactivity in women aged 31 to 36
On average, the population
attributable risk was:
• 48% in the younger cohort
(aged 22 to 39)
• 33% in the mid-aged cohort
(aged 47 to 64)
• 24% in the older cohort (aged
73 to 90)
How did the researchers interpret
the results? The researchers
concluded that, “From about age 30,
the population risk of heart disease
attributable to inactivity outweighs
that for other risk factors, including
high BMI.
“Programmes for the promotion
and maintenance of physical activity
deserve to be a much higher public
health priority for women than they
are now, across the adult lifespan.”
Conclusion. This study has found
that the proportion of heart disease
attributable to four risk factors
(smoking, high BMI, high blood
pressure and physical inactivity)
in Australian women changes with
age.
The figures calculated in
this study – called population
attributable risk – indicate the
proportion of cases that would
not occur in a population if risk
factors were eliminated. Population
attributable risk depends on the
increase in risk of heart disease
associated with the factor, and the
number of women with the risk
factor.
A risk factor could have the
if it is the most common risk factor
in a population. But this is not
necessarily because it is associated
with the greatest increase in risk for
the individual.
This study has found that
smoking had the highest population
attributable risk in women under
30. If women in this age group gave
up smoking, approximately 55-60%
of cases of heart disease would be
estimated to be eliminated.
In women aged 30 or over,
physical inactivity (low or no
physical activity) had the highest
population attributable risk of the
four factors assessed. If inactive
women aged 31 to 36 increased
their physical activity, about 51%
of cases of heart disease could be
eliminated.
The population attributable risk
for inactivity was lower in older age
groups, but if women aged 47 to 64
increased their physical activity,
33% of heart disease cases could be
eliminated. If women aged 73 to 90
did the same, 24% of heart disease
cases could be eliminated.
One important factor to note is
that these population attributable
risk figures are estimates designed
to give an indication of the
maximum effect that might be
achieved by removing these risk
factors. Achieving this change may
be difficult.
The estimates also do not take
into account interactions between
these and other risk factors. They
therefore may overestimate the
impact of each factor individually.
As population attributable factors
take into account the prevalence of
risk factors, they will also change
depending on how common a risk
factor is, and will therefore differ
across populations with different
behaviours and characteristics.
Overall, the findings of this study
do not change the message for
individuals about the importance
of reducing unhealthy behaviours
such as smoking, and making sure
we stay active.
If you are concerned about your
fitness level, why not try the NHS
fitness plan, which is designed to
get fitness phobes up to speed in 12
weeks. n NHS Choices