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Consumers were left more confused than ever
when the media reported on two obesity-related
studies from the Journal of the
American Medical Association last week. One
seemed to find it was more important to be fit
than thin for your heart health; the other that it
was more important to be thin than fit to prevent
diabetes. As Eric Berger of the Houston
Chronicle wrote, the two studies disagreed
and settled "nothing"
in the debate over what matters most to a person's
health: his overall fitness or his weight.
But in fact, the controversy has already been
repeatedly answered in the scientific literature.
The trouble is, it's not what a lot of people want
to hear...and others without science backgrounds
don't realize.
These side-by-side JAMA studies provided an
invaluable opportunity for the media to help
consumers sort through medical information and
come away with a very important message: not all
studies are created equal.
Most anything can be and
is called a "study" nowadays and many aren't
actual clinical studies or even examining real
people. That surprises many consumers. Medical
news is all too often taken at face value. But
before believing headlines or making any changes
or decisions about one's health, it's important to
know that some studies are sounder and have more
validity than others. So those "should have more
influence," said Dr. Peter Jones, an associate
professor of medicine at Baylor. A study also
needs to be considered in light of the entire body
of scientific evidence.
When we look at these
two JAMA studies, their differences quickly become
apparent.
When a
Study Isn't a Study
The first study led by
Amy Weinstein, MD claimed to find obesity was more
important in predicting type 2 diabetes than
physical activity. This was a type of study often
called a "data dredge" because it mines a large
database of characteristics from a population,
looking for correlations. This study used numbers
from the Women's Health Study -- a database of
questionnaires collected from nearly 40,000 women
since 1992, based at Brigham and Women's Hospital
in Boston. I call these databanks "Rorschach
tests" of epidemiology, because researchers can
pull out numbers in almost unlimited combinations
to find all sorts of correlations and conclude
just about anything they set out to find. Just
like the Rorschach test, seeing patterns where
none exists, finding connections that are there
but not as strongly as believed, and seeing what
one expects to see, are common.
The biggest and
longest-running Rorschach test is the Nurses
Health Study -- a huge quarry of questionnaires
(essentially unverified anecdotes) gathered since
1976 from over 120,000 nurses, headed by JoAnne
Manson, MD, DrPH of Brigham and Women's Hospital
in Boston. Over 500 "studies" have been released
all using the Nurses Health Study numbers and,
interestingly, they frequently disagree. You may
remember they reported just a week ago that sugary
drinks were associated with obesity and type 2
diabetes. That contradicted their own earlier 2002
"study" which found sugar and glycemic load was
unrelated to diabetes or weight.
No wonder consumers are
confused -- hearing "science" has found one thing
one day, only to find something entirely different
the next. My advice is to ignore these data dredge
studies. Wait until a real study comes
out.
These types of
epidemiological studies can only manipulate
numbers from groups of people to find possible
relationships. They were never meant to apply to
individuals, nor can they ever show a cause for
anything because they don't actually test
anything. Their purpose is to identify possible
hypotheses for later clinical tests, which can
then try to identify if and explain why something
happens. But correlations themselves can never
prove causation. For example, ice cream sales
correlate with drownings, as the winner of the
Purdue University 1998 Spurious
Correlations Contest noted, but it is not
sound to conclude that ice cream causes drownings!
Yet even to claim a
correlation in these types of studies, it must
also be statistically significant enough to be
over what one would find by chance -- more than
the toss of the dice -- or due to error, missing
relevant factors, or statistical bias. So
scientists do not take as credible anything which
doesn't appear two to three times over baseline,
or a 100- to 200-percent difference. The National
Cancer Institute found anything less than 100
percent wasn't tenable.
But Ernst Wynder, MD, founder and director of the
American Health Foundation and editor of Preventative
Medicine prior to his death, said anything
less than three is suspect. And Marcia Angell, MD,
former editor-in-chief of the New England
Journal of Medicine said they looked for three
or more before accepting a study for publication.
Yet, we frequently see epidemiological findings of
5-, 30- or 50-percent reported as if that means
anything.
Type 2 diabetes appears
to be correlated to obesity but it and the
"diabetes epidemic" are just as spurious as ice
cream. Rising diabetes rates can also be partially
explained by an aging population, increased
awareness and testing for the condition, and
because of changes in the definition itself.
Just like "overweight,"
diabetes has been redefined to include increasing
numbers of the population. It used to be defined
as fasting blood sugars >140, in 1998 that was
changed to >126, and last November they deemed
100 abnormal, creating a new malady "prediabetes."
That latest change alone added another 40 percent
of the adult population to the roster in need of
treatment, according to Dr. Frank Vinicor,
diabetes chief for the Centers for Disease Control
and Prevention. Vinicor told CNN on April 29,
lowering the cut-off was "based on emerging
science from the last two to three years." But
others question if prediabetes even exists.
According to Paul Zimmet, MD, PhD, world-renowned
diabetes researcher and founding director of the
International Diabetes Institute, it may be
"inappropriate to use the term 'prediabetes' when
there is only a 50% chance of developing diabetes
in the next ten years."
Sadly data dredge studies are
increasingly being misused and misinterpreted. In
the Weinstein study, you'll see several classic
strategies identified by Dr. John
Brignell, PhD in The
Epidemiologists: Have they got scares for you!
(Brignell, 2004). For
example:
·The trojan
horse number to increase the impressiveness of
the study. They claimed the study was of nearly
38,000 women, yet the researchers actually only
clinically confirmed type 2 diabetes in 89 women
of the (1361) self-reported cases.
·
The
authors selected the characteristics they wanted
to look at, but disregarded ones they didn't, and
didn't even consider factors that might have been
important, such as race and ethnicity. The groups
with different body mass indexes were similar in
many lifestyle factors, except the slender group
drank three times more alcohol than the fat group.
But you sure didn't hear them conclude that
drinking alcohol, especially more than one drink a
day, prevents diabetes!
·
Another
notable drawback to this study is that it relied
on self-reported information of recreational
physical activity. That's a more nebulous way to
arrive at determinations of metabolic fitness than
studying fitness on a treadmill, for
example.
Most noteworthy is that
this study's findings contradict many stronger
clinical and epidemiological studies that have
found that exercise reduces type 2 diabetes and
improves insulin resistance, unrelated to weight.
For example, researchers at the Cooper Institute
in Dallas, Texas led by Timothy S. Church, MD,
PhD, followed over 2,000 diabetics for 25 years,
using a range of health assessments, including
treadmill tests to gauge their fitness levels.
They found that premature deaths from all causes
were significantly lower among the fit. Weight was
irrelevant. Researchers at the Veterans Affairs,
Palo Alto Health Care System, Stanford University
studied over 6,000 men for six years and found
exercise capacity was more important in risks of
dying than "known" risk factors including obesity,
cholesterol, hypertension, smoking and even
diabetes. Even a small clinical study at Queen's
University, Kingston, Ontario, Canada following 54
obese women found daily exercise, without dieting
or weight loss, substantially reduced insulin
resistance in just 14
weeks.
Studies on Real
People
Which brings us to that
second study led by Timothy R. Wessel, MD. It
concluded that being fit significantly reduces
heart attacks, strokes and heart problems among
women. Weight was again irrelevant. It was a
cohort study -- a type of study where researchers
gather clinical information on a group of people
and then follow them, observing their health
outcomes. The soundness of the data they used is
notably superior to the Weinstein study. For four
years, the researchers followed more than 900
women who had been examined at four major medical
centers using multiple clinical diagnostic tests
of heart disease and correlated it with treadmill
capacity assessments.
Most significant, this
study is just one of dozens of clinical studies
over decades which have found the exact same thing
in men and women: when fitness is considered,
weight is irrelevant to long-term health, heart
disease, diabetes or premature death from all
causes.
The list is too
extensive to cite here, but clinical studies
concluding 'fitness not weight is what counts'
include the Harvard Alumni Health Study of 12,516
men followed for 16 years; the St. James Women
Take Heart Project of 5,721 women studied for 8
years; and the Aerobics Center Longitudinal Study,
an ongoing study that includes 25,389 patients
examined at the Cooper Clinic in Dallas from 1970
to 1989. Even the Women's Health Study published
findings in 2001 that found merely light to
moderate activity was dramatically associated with
lowered heart disease in women, including those
who were overweight, had high cholesterol or
smoked.
Ending the Debate
What the public didn't
read last week was a poignant editorial in this
same issue of JAMA by Dr. Steven Blair, PED and
Dr. Church, of the Cooper Institute for Aerobic
Research in Dallas, Texas, where much of the
country's landmark research on fitness and
preventative health has been done. They chastised
today's obesity researchers, saying that "failure
to adequately quantify physical activity when
examining the risks of obesity is similar to
exploring risk factors for cancer and
misclassifying tobacco use."
Drs. Blair and Church
emphasized that death rates and heart disease
among obese people, with just moderate fitness,
are half that
of "normal" weight people who aren't fit. The
amount of exercise to attain this health-giving
level of moderate fitness isn't much, either, and
has been proven in 24 clinical studies: it's
merely 150 minutes of moderate-intensity activity
a week. They say that's equivalent to 30 minutes,
5 times a week of: walking, gardening, housework,
bicycling, swimming or other activities enjoyed in
daily life.
Now that's news that people
can use.
This article originally
appeared in Tech Central Station http://www.techcentralstation.com |
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