Little Doubt Left that Severe Obesity Can Lead to
Heart Failure
Study in 7,000 men and women ties obesity,
inflammatory proteins to heart failure
May
1, 2008 - Any remaining doubt that being severely overweight leads to
heart failure was probably erased today by the release of what is
described as the first wide-scale evidence of prolonged inflammation and
resulting damage to heart tissue causing failure of the body's
blood-pumping organ among the obese.
The latest findings from the Multiethnic Study of
Atherosclerosis (MESA), to be published in the May 6 issue of the
Journal of the American College of Cardiology, appear to nail down yet
one more reason for the estimated 72 million obese American adults to be
concerned about their health, say scientists who conducted the research.
“The biological effects of obesity on the heart are
quite profound,” says senior study investigator João Lima, M.D. “Even if
obese people feel otherwise healthy, there are measurable and early
chemical signs of damage to their heart, beyond the well-known
implications for diabetes and high blood pressure.”
He adds that there is “now even more reason for
them to lose weight, increase their physical activity and improve their
eating habits.”
In the latest study, researchers conducted tests
and tracked the development of heart failure in an ethnically diverse
group of nearly 7,000 men and women, age 45 to 84, who were enrolled in
the MESA study, starting in 2000.
Of the 79 who have developed congestive heart
failure so far, 35 (44 percent) were physically obese, having a body
mass index, or BMI, of 30 or greater. And on average, obese participants
were found to have higher blood levels of interleukin 6, C-reactive
protein and fibrinogen, key immune system proteins involved in
inflammation, than non-obese adults.
A near doubling of average interleukin 6 levels
alone accounted for an 84 percent greater risk of developing heart
failure in the study population.
The researchers from Johns Hopkins and four other
universities across the United States also found alarming links between
inflammation and the dangerous mix of heart disease risk factors known
as the metabolic syndrome. Its combined risk factors for heart disease
and diabetes - high blood pressure, elevated blood glucose levels,
excess abdominal fat and abnormal cholesterol levels, and particularly
obesity - double a person’s chances of developing heart failure.
“More practically, physicians need to monitor their
obese patients for early signs of inflammation in the heart and to use
this information in determining how aggressively to treat the
condition,” says Lima, a professor of medicine and radiology at the
Johns Hopkins University School of Medicine and its Heart Institute.
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All MESA study participants, who will be followed
through to 2012, had no pre-existing symptoms of heart disease. Upon
enrollment, they all underwent a physical exam, including weight and
body measurements, blood analysis and an MRI scan to assess heart
function.
“Our results showed that when the effects of other
known disease risk factors - including race, age, sex, diabetes, high
blood pressure, smoking, family history and blood cholesterol levels -
were statistically removed from the analysis, inflammatory chemicals in
the blood of obese participants stood out as key predictors of who got
heart failure,” says Lima.
The chemicals are all known to be part of the
body’s defensive response to disease. They are well-recognized for
producing symptoms that stem from the widening of small blood vessels,
including redness and fever, and the release of immune system cells that
make blood vessels leak fluid into surrounding tissue, causing swelling
and cell death. The inflammatory process eventually leads to cell damage
and the buildup of scar tissue near the damaged areas.
In obese participants, interleukin 6, a chemical
that activates white blood cells and drives inflammation, was higher
than in non-obese participants.
Similarly, a near tripling of average levels of
C-reactive protein in study participants increased the chance of heart
failure by 36 percent.
C-reactive protein levels are widely known to rise
dramatically and speed up the early stages of inflammation when cells
swell up with fluid, leading to widespread arterial damage.
One-fifth higher than average blood levels of
fibrinogen, best known for its role in blood clotting but also a major
player in muscle scarring, bumped up the risk of heart failure by 37
percent.
When the inflammatory protein levels were included
in the scientists’ statistical analysis, the heightened risk from
obesity disappeared.
“What this tells us is that both obesity and the
inflammatory markers are closely tied to each other and to heart
failure,” says lead researcher Hossein Bahrami, M.D., M.P.H.
Each year, nearly 300,000 Americans die from heart
failure.
Bahrami says study results also point to
inflammation as a possible catalyst in metabolic syndrome. Increased
blood levels of albuminuria, a chemical more known for its association
with impaired kidney function and metabolic syndrome boosted risk of a
progressively weakening heart nearly tenfold among MESA participants.
Bahrami, a senior cardiology research fellow at
Hopkins, says “the basic evidence is building the case that inflammation
may be the chemical route by which obesity targets the heart, and that
inflammation may play an important role in the increased risk of heart
failure in obese people, especially those with the metabolic syndrome.”
He notes that previous studies, also done at
Hopkins, have shown that even moderate exercise to lose abdominal fat
dramatically offsets the harmful effects of metabolic syndrome on heart
function.
Bahrami says the team’s next steps are to determine
how, over a longer timeframe, heart function changes with levels of
inflammatory markers, and to see if alterations to the immune system
proteins halts or speeds up disease.
Editor's Notes:
BMI is calculated from a person’s weight and height
and serves as a good indicator of overall body fatness (where a person’s
weight in kilograms is divided by the square of height in meters; or
using weight in pounds, divided by the height in inches squared,
multiplied by a metric conversion factor of 703.)
MESA is funded by the National Heart, Lung and
Blood Institute, a member of the National Institutes of Health.
Besides Lima and Bahrami, other Hopkins
investigator involved in this study were David Bluemke, M.D., Ph.D., and
Moyses Szklo, M.D., Dr.P.H. Study co-authors were Richard Kronmal,
Ph.D., from the University of Washington in Seattle; Alain Bertoni,
M.D., M.P.H., from Wake Forest University in Winston-Salem, N.C.; Donald
Lloyd-Jones, M.D., Sc.M., from Northwestern University in Chicago; and
Eyal Shahar, M.D., M.P.H., from the University of Arizona.
May
1, 2008 - Any remaining doubt that being severely overweight leads to
heart failure was probably erased today by the release of what is
described as the first wide-scale evidence of prolonged inflammation and
resulting damage to heart tissue causing failure of the body's
blood-pumping organ among the obese.
