Tuesday August 14 2007
Does a pot belly put you at risk?
Even a small pot belly is associated with a greater risk of heart disease, reported The Times. People with even a little fat around their waists are “significantly more vulnerable to heart disease, even if their overall weight was normal”, the newspaper explained.
The Daily Telegraph stated that this research indicates that measuring the waist-to-hip ratio may be “more important than the body mass index (BMI)”. It reported that men with a waist-to-hip ratio of more than one, and women with a ratio of 0.8 or more, are at greatest risk.
These reports are based on a relatively large study in the US, which compared how common atherosclerosis (the build-up of fatty deposits within the arteries and hardening of the artery walls that can restrict blood flow and increase the risk of a heart attack) was in people with and without certain indicators of obesity, such as a high waist-to-hip ratio or a high BMI. The findings do indicate an association between the waist-to-hip ratio and atherosclerosis. However, it remains to be seen how much this measurement can add to existing cardiovascular risk assessments, or whether the waist-to-hip ratio can be used to predict symptomatic heart disease.
Where did the story come from?
Raphael See, James de Lemos and colleagues at the University of Texas Southwestern Medical Center carried out the research. It was funded by the Donald W Reynolds Foundation and National Institutes for Health and was published in the peer-reviewed medical journal Journal of the American College of Cardiology.
What kind of scientific study was this?
The researchers used cross sectional data from almost 3,000 18 to 65-year-olds who were enrolled in the Dallas Heart study between 2000 and 2002. This study was set up to look at heart health in a community-wide study. This part of the study aimed to assess whether there was an association between different measures of obesity, such as body mass index and waist-to-hip ratio, and atherosclerosis.
The researchers measured the participants’ waist and hip measurements, and calculated their body mass index (BMI) based on their height and weight. This data gave a measure of how overweight or obese participants were. Researchers then used sophisticated imaging machinery to look at the blood vessels supplying the participants’ hearts (the coronary arteries) and see how much calcium had built up in the walls of these arteries. A significant build-up of calcium in the vessels indicated that the participant had atherosclerosis.
The participants were then divided into five groups based on how high their waist and hip measurements, their waist-to-hip ratios and their BMIs were. The researchers then compared the number of people with atherosclerosis in the four groups who had the highest levels of obesity measurements with the fifth group of people, who had the lowest obesity measurements (the slimmest group). Statistical methods were used to adjust for other factors that might influence how likely a person was to have atherosclerosis, including age, levels of cholesterol and other fats in the blood, being a smoker, high blood pressure or diabetes. The researchers also looked at whether adding any of these obesity measurements to the traditional risk factor assessments would improve the performance of these assessments for predicting atherosclerosis.
What were the results of the study?
researchers found that the 20% of people with the highest waist-to-hip ratios were significantly more likely to have atherosclerosis than the 20% of people with the lowest waist-to-hip ratios.
They also found that the people with higher BMIs and waist circumferences were not significantly more likely to have atherosclerosis than the people with the lowest BMIs and waist circumferences, once adjustments were made for traditional risk factors.
However, adding any of these obesity measurements to traditional risk factor assessments did not significantly improve the ability to identify people with atherosclerosis.
What interpretations did the researchers draw from these results?
The researchers concluded that high waist-to-hip ratios are associated with the presence of atherosclerosis independently of traditional risk factors, and are better predictors of the presence of atherosclerosis than BMI. They also suggest that their findings indicate that obesity may increase cardiovascular mortality by increasing atherosclerosis.
What does the NHS Knowledge Service make of this study?
This was a relatively large study, which shows that waist-to-hip ratio may be a better indicator of whether a person has atherosclerosis than BMI. However, a number of factors should be considered when interpreting this study:
- This study only looked at people who had no symptoms of atherosclerosis. This study did not look at association between obesity measurements and symptomatic heart disease, and therefore conclusions about any potential relationships between these outcomes cannot be drawn.
- The results of this study cannot be interpreted to mean that a high waist-to-hip ratio causes atherosclerosis, because the study does not establish the sequence of events; that is, it does not tell us whether people develop a high waist-to-hip ratio before they develop atherosclerosis.
- The study found that adding a measurement of waist-to-hip ratio to traditional risk assessment tools may not improve their performance in identifying who has atherosclerosis.