Thursday November 13 2008
“The size of your waist is a more important determinant of health than your weight,” The Independent said today. It reported that one of the largest studies conducted into waist size and health found that people with a large waist have a greater likelihood of a premature death - even if they are slim. It said those with a large waist had twice the risk of dying early.
Obesity is often measured using the body mass index (BMI) which is a calculation of an individual’s weight and height. This study of more than 350,000 people highlights that measurements of BMI can be reliably supplemented with waist measurements. The link is already well known and this study may mean that waists are now more commonly measured in general practice.
These researchers say that it is important to consider where fat accumulates as well as how much total fat there is. Their conclusion that it is better to be a pear shape (narrow waists and wide hips) rather than an apple shape (wide waist and narrow hips) should be endorsed.
Where did the story come from?
Dr Tobias Pischon from the German Institute of Human Nutrition in Potsdam-Rehbruecke, Germany, carried out this research with over 40 colleagues from around Europe. The research was supported by grants from several public and private research agencies, cancer societies and foundations. The study was published in the peer-reviewed The New England Journal of Medicine.
What kind of scientific study was this?
In this prospective cohort study, the researchers aimed to clarify the relationship between abdominal obesity, using either measurements of waist circumference or waist–to-hip ratio, with the risk of death.
It is known that these measurements are linked with the risk of disease. International guidelines define abdominal obesity in people who already have a BMI of between 25.0 and 34.9 as:
- a waist circumference of at least 102cm in men and 88cm in women, or
- a waist-to-hip ratio of 1.0 in men and 0.85 in women
The European Prospective Investigation into Cancer and Nutrition (EPIC) study has data on 519,978 men and women between the ages of 25 and 70. These people were enrolled between 1992 and 2000 from the general population of towns or provinces in 10 European countries (Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden, and the United Kingdom). The researchers excluded any participants who withdrew from the study and others where there was missing data. After these exclusions, the researchers were left with 359,387 participants for analysis.
The participants had their weight and height measured when they were clothed and not wearing shoes. Waist circumference was measured either at the narrowest circumference of the body or at the midpoint between the lower ribs and the bony part of the hip/pelvis. The participants were then separated into five categories according to their increasing waist circumference. Their hip circumference was measured horizontally at the level of the largest bulge of the hips or over the buttocks. Cause of death was collected from the national cancer registries and death indexes.
The researchers used statistical methods to adjust for a range of factors that could have influenced the results, such as smoking, educational achievement, alcohol consumption and physical activity.
What were the results of the study?
The study ran for 9.7 years during which 14,723 participants (out of about 360,000) died. Men with a BMI of 25.3 and women with a BMI of 24.3 had the lowest risk of death. The participants’ BMI, waist circumference and waist-to-hip ratio were all strongly associated with their risk of death. This was still significant after statistical adjustment for smoking, educational achievement, alcohol consumption and physical activity.
When comparing the chance of dying between the participants with the largest waist circumference and the participants with the smallest, the researchers found that men with the largest waists had nearly double the risk (RR 2.05; 95% CI 1.80 to 2.33) and women had just under double the risk (RR 1.78; 95% CI, 1.56 to 2.04).
BMI remained significantly associated with the risk of death when waist circumference or waist-to-hip ratio were also taken into account (P<0.001), suggesting that both BMI and waist circumference are independent and important indicators of risk.
What interpretations did the researchers draw from these results?
The researchers say that both “general adiposity [fat] and abdominal adiposity are associated with the risk of death” and that the findings mean that waist circumference or waist-to-hip ratio should be measured in addition to BMI when assessing the risk of death.
What does the NHS Knowledge Service make of this study?
The findings from this large study corroborates what has been found in previous studies and confirms what is already generally accepted knowledge. However, one benefit of this study is that it was in a large European population, and so the results can be directly applied to the UK population.
One possible limitation of the study is that the technique of measuring waist circumference is difficult to standardise. It is possible that there is some variation between how the researchers measured it in different parts of the study and this would have led to some inaccuracy in the measurements. For example, the researchers mention that the results in the Greek arm of the study showed systematic differences that could have been explained by the different technique of measurement. However, they were not certain if it was the different measurement technique, if there could have been real differences in the Greek populations waist size or even if the differences had arisen by chance. They say any analysis of the differences between the sub groups, which each have few participants, should be treated with caution.
In general, this is a reliable study which reinforces the use of waist circumference as a measurement for identifying people at higher risk of death. The findings strengthen the advice that people should aim to be a “slim pear” shape rather than a “large apple”.