More belly weight increases danger of heart disease even if BMI does not indicate obesity
American Heart Association
"This scientific statement provides the most recent research and information on the relationship between obesity and obesity treatment in coronary heart disease, heart failure and arrhythmias," said Tiffany M. Powell-Wiley, M.D., M.P.H., FAHA, chair of the writing committee and a Stadtman Tenure-Track Investigator and chief of the Social Determinants of Obesity and Cardiovascular Risk Laboratory in the Division of Intramural Research at the National Heart, Lung, and Blood Institute at the National Institutes of Health in Bethesda, Maryland.
"The timing of this information is important because the obesity
epidemic contributes significantly to the global burden of cardiovascular
disease and numerous chronic health conditions that also impact heart disease."
A
greater understanding of obesity and its impact on cardiovascular health
highlights abdominal obesity, sometimes referred to as visceral adipose tissue,
or VAT, as a cardiovascular disease risk marker. VAT is commonly determined by
waist circumference, the ratio of waist circumference to height (taking body
size into account) or waist-to-hip ratio, which has been shown to predict
cardiovascular death independent of BMI.
Experts
recommend both abdominal measurement and BMI be assessed during regular health
care visits because a high waist circumference or low waist-to-hip ratio, even
in healthy weight individuals, could mean an increased risk of heart disease.
Abdominal obesity is also linked to fat accumulation around the liver that
often leads to non-alcoholic fatty liver disease, which adds to cardiovascular
disease risk.
"Studies that have examined the relationship between abdominal fat and cardiovascular outcomes confirm that visceral fat is a clear health hazard," said Powell-Wiley.
The
risk-inducing power of abdominal obesity is so strong that in people who are
overweight or have obesity based on BMI, low levels of fat tissue around their
midsection and organs could still indicate lower cardiovascular disease risks.
This concept, referred to as "metabolically healthy obesity," seems
to differ depending on race/ethnicity and sex.
Worldwide, around 3 billion people are overweight (BMI = 25 to 29.9 kg/m2) or have obesity obese(BMI ?30 kg/m2). Obesity is a complex disease related to many factors, including biologic, psychological, environmental and societal aspects, all of which may contribute to a person's risk for obesity.
Obesity is associated with
greater risk of coronary artery disease and death due to cardiovascular disease
and contributes to many cardiovascular risk factors and other health
conditions, including dyslipidemia (high cholesterol), type 2 diabetes, high
blood pressure and sleep disorders.
For this statement, experts evaluated research on managing and treating obesity, particularly abdominal obesity. The writing group reports that reducing calories can reduce abdominal fat, and the most beneficial physical activity to reduce abdominal obesity is aerobic exercise.
Their analysis found that meeting
the current recommendations of 150 min/week of physical activity may be
sufficient to reduce abdominal fat, with no additional loss from longer
activity times. Exercise or a combination of dietary change and physical
activity has been shown in some instances to reduce abdominal obesity even
without weight loss.
Lifestyle
changes and subsequent weight loss improve blood sugar, blood pressure,
triglyceride and cholesterol levels -- a cluster of factors referred to as
metabolic syndrome -- and reduce inflammation, improve blood vessel function
and treat non-alcoholic fatty liver disease. However, studies of lifestyle
change programs have not shown a reduction in coronary artery disease events
(such as heart attack or chest pain).
In
contrast, bariatric surgery for weight loss treatment is associated with a reduction
in coronary artery disease risk compared to non-surgical weight loss. This
difference may be attributed to the larger amount of weight loss and the
resultant changes in metabolism that are typical after bariatric surgery.
"Additional
work is needed to identify effective interventions for patients with obesity
that improve cardiovascular disease outcomes and reduce cardiovascular disease
mortality, as is seen with bariatric surgery," said Powell-Wiley.
The
statement also addresses the "obesity paradox," which is sometimes
observed in research, particularly in populations that have overweight or have
Class I obesity (BMI = 30 to 34.9 kg/m2). The paradox suggests that even though
overweight and obesity are strong risk factors for the development of cardiovascular
disease, they are not always a risk factor for negative cardiovascular
outcomes. The writing group notes that people with overweight or obesity are
often screened earlier for cardiovascular disease than people with healthy
weight, thus resulting in earlier diagnoses and treatment.
"The
underlying mechanisms for the obesity paradox remain unclear," said
Powell-Wiley. "Despite the existence of the paradox for short-term
cardiovascular disease outcomes, the data show that patients with overweight or
obesity suffer from cardiovascular disease events at an earlier age, live with
cardiovascular disease for more of their lives and have a shorter average
lifespan than patients with normal weight."
In
reviewing the effects of obesity on a common heart rhythm disorder, the writing
group reports there is now "convincing data" that obesity may cause
atrial fibrillation, a quivering or irregular heartbeat. Estimates suggest
obesity may account for one-fifth of all atrial fibrillation cases and 60% of
recently documented increases in people with atrial fibrillation. Research has
demonstrated people with atrial fibrillation who had intense weight loss
experienced a significant reduction in cumulative time spent in atrial
fibrillation.
"The
research provides strong evidence that weight management be included as an
essential aspect of managing atrial fibrillation, in addition to the standard
treatments to control heart rate, rhythm and clotting risk," said
Powell-Wiley.
The
statement identifies areas of future research, including a call for further
study of lifestyle interventions that may be most effective in decreasing
visceral adiposity and improving cardiovascular outcomes. Powell-Wiley said,
"It's important to understand how nutrition can be personalized based on
genetics or other markers for cardiovascular disease risk.
She
added, "as overweight and obesity prevalence increases among adolescents
worldwide, it is critical to address how best to develop upstream primary
prevention interventions and better treatment strategies, particularly for
young patients with severe obesity."
