The importance of waist circumference
A marker of high risk internal fat
Body Mass index (BMI) is simply a ratio of weight in relation to height. BMI is not a direct measurement of body fat, and importantly this ratio provides no information about distribution of body fat.
In contrast, the measurement of waist circumference provides information regarding fat topography - where body fat is stored. This is important because people who carry their weight centrally are particularly at risk of developing heart disease and type 2 diabetes. As you can see from the graph below, waist circumference is a good indicator of high risk intra-abdominal or visceral fat accumulation.
Visceral fat in particular appears to be associated with insulin resistance which leads to type 2 diabetes. Visceral fat is also associated with adverse lipid profiles which in turn predispose to cardiovascular disease.
Determining an individual's waist circumference measurement helps to target treatment towards particularly at-risk patients who have a tendency to store their excess weight centrally1. For this reason, waist circumference measurement is increasingly recognised as being a more important tool than simple BMI measurement in assessing an individual's health risks associated with overweight and obesity.
Measuring waist: measuring risk
Several large multinational studies involving many thousands of people, such as IDEA, INTERHEART, EPIC and the US Cancer Prevention Study II Nutrition Cohort, have confirmed that measurement of abdominal obesity and central fat accumulation is an important tool in assessing risk of heart disease, risk of developing type 2 diabetes and risk of death.
International Day for the Evaluation of Abdominal Obesity (IDEA)
This international study involved the measurement of BMI and waist circumference of 168,000 patients by randomly chosen physicians in primary care in 63 countries and simultaneously recording, from the patients medical notes, the presence of cardiovascular disease (defined as history of coronary heart disease, stroke or revascularisation) and diabetes (type 1 or type 2 diabetes) in these patients.2
The study took place in 2005 over two specified half days. Ninety-seven percent of the eligible patients aged between 18-80 years who attended to see their GPs at the time when IDEA data collection was taking place agreed to participate in this study.
The IDEA study demonstrated a statistically significant graded increase in the frequency of cardiovascular disease and diabetes with both BMI and waist circumference. Importantly a stronger relationship was observed for waist circumference than was observed for BMI in relation to cardiovascular disease and diabetes. This finding was demonstrated observed for both men and women across the regions studied as part of this international investigation.
IDEA study findings: waist circumference and cardiovascular disease
Waist circumference was divided into five categories or quintiles during data analysis as part of the IDEA study. Men in the highest waist circumference quintile (≥107cm) had 2.2 times more cardiovascular disease than those in the lowest quintile (<84cm); for women, when the most abdominally obese quintile were compared to the least abdominally obese quintile (≥101 versus <76cm), the ratio was 2.6
IDEA study findings: waist circumference and diabetes
The frequency of diabetes showed an even stronger graded increase across waist circumference quintiles; in men it increased >3-fold (from 5.7% diabetes prevalence in the lowest waist circumference quintile group to 19.4% diabetes prevalence in the highest waist circumference quintile group) and in women it increased by almost 6 fold (3.1% to 17.8%)
Furthermore the IDEA study demonstrated that the frequency of both cardiovascular disease and diabetes increased with increasing waist circumference within each BMI category and both cardiovascular disease and diabetes were significantly associated with increased waist circumference even in lean individuals (BMI<25kg/m2)
Abdominal obesity and risk of heart attack (INTERHEART)
The INTERHEART study was published in the Lancet in 20043. This multinational study took place in 52 countries and involved approximately 15,000 patients who had suffered a heart attack, and a similar number of "control patients" who were in hospital for other reasons.
The INTERHEART study gathered data to determine the 9 most important risk factors which contributed over 90% of the risk of having a heart attack in the 16,000 patients studied.
This study confirmed that central fat accumulation or abdominal obesity contributed as much risk to developing heart disease as smoking (odds ratio 2.24 for abdominal obesity vs. 2.27 for smoking)
Waist circumference and all-cause mortality (EPIC)
The European Prospective Investigation into Cancer and Nutrition (EPIC) study has followed up almost 360,000 patients for approximately 10 years4. Patients were categorised as being in one of five waist circumference ranges ("quintiles"). Those in the highest quintile for waist circumference were found to have double the risk of death from all causes compared to those within the lower waist circumference quintile over the 10 year period of follow up.
For every 5cm of waist circumference the study demonstrated a 17% increased relative risk of death for men and 13% for women that was independent of BMI category.
Waist circumference as a risk factor for mortality, regardless of BMI
The association between waist circumference and mortality was examined amongst 48,500 men and 56,343 women aged over 50 years who participated in the US Cancer Prevention Study II Nutrition Cohort5.
Importantly, this study examined the association waist circumference and mortality within each of the standard BMI categories (normal, overweight and obese).
This study also examined mortality in relation to higher levels of waist circumference of >120cm for men and >110cm for women, which are now common.
In this large study, a total of 9315 men and 5332 women died between 1997 and follow up in 2006.
Any waist circumference greater than the smallest sizes (less than 90cm in men and less than 75cm in women) was associated with higher mortality. The mortality risk increased linearly with increasing waist circumference both in men and women.
Waist circumference was related to mortality even within the standard BMI categories.
For men the relative risk of mortality rose 16% (within the normal BMI category), 18% (within the overweight BMI category) and 21% (within the obese BMI category) with every 10cm increase in waist circumference.
For women, it is notable that in this study, the relative risk with every 10cm increase in waist circumference was greatest within the normal BMI category, with a 25% increased relative mortality risk. Within the overweight BMI category, the relative risk increase with each 10cm increase in waist circumference was 15% and in the overweight BMI category, and 13% in the obese BMI category.
These findings suggests that a normal BMI may underestimate risk in the context of an increased waist circumference, particularly in women greater than 50 years of age, but also in men with a 16% relative increased mortality risk with every 10cm increase in waist circumference, regardless of their body weight being within a normal BMI category.
These findings have important implications in the light of the fact that current clinical guidelines do not address waist circumference in normal-weight patients and do not recommend weight loss for abdominally obese patients unless they have a high BMI.
Higher levels of waist circumference in men (>120cm) were associated with a 2-fold relative risk of mortality when compared to waist circumferences <90cm.
In women high level of waist circumference >100cm were associated with a 2.4-fold relative risk of mortality when compared to waist circumferences <75cm.
Waist circumference associated with all-cause mortality
The present study, like the EPIC study described above, identifies an association between waist circumference and all-cause mortality. When analysed by cause of death, the link between waist circumference and mortality was strongest from respiratory causes, followed by cardiovascular disease and then cancer.
What can we learn from this study?
The results of this large prospective study emphasize the importance of waist circumference as a risk factor for mortality in older adults, regardless of whether the BMI is categorised as normal, overweight or obese. The results suggest that regardless of weight, avoiding gains in waist circumference may reduce the risk of premature mortality.
Targeting those at risk
The important message is that the high-risk internal fat store is preferentially reduced as a result of moderate weight loss and waist reduction. A waist reduction of just 5cm can significantly reduce risk.
The table below provides waist circumference cut-off values to help determine those at risk, according to sex and ethnicity6.
|Ethnic South & Central American||Use South Asian recommendations||Use South Asian recommendations|
|Sub-Saharan Africans||Use European data||Use European data|
|Eastern Mediterranean & Middle East (Arab) populations||Use European data||Use European data|
Screening high-risk abdominally obese patients and supporting attempts at moderate weight and waist reduction is a vitally important aspect of diabetes and cardiovascular disease prevention.
The hypertriglyceridaemic waist
The combination of a raised waist circumference measurement and blood test result demonstrating raised fasting triglyceride level ≥2.0 mmol/L categorises the "hypertriglyceridaemic waist phenotype"7. This combination of increased waist measurement and raised fasting triglycerides is an easy way to identify those who are likely to have accumulated high risk intra-abdominal or visceral fat.
Those individuals who have the "hypertriglyceridaemic waist phenotype" are at increased risk of cardiovascular disease8,9 and have the most to gain from reductions in waist circumference and the visceral fat depot through appropriate lifestyle change and weight management interventions.
It is important for healthcare professionals to appreciate that fat is lost from high risk sites first, and reduction in waist circumference in at-risk patients is commonly associated in reduction in blood pressure and markers of metabolic obesity such as fasting triglycerides, ALT as a marker of fatty liver disease (NASH), and also a reduction insulin resistance and improvements in glucose metabolism.
1. Despres J-P, lemieux I, Prud'homme D. Treatment of obesity: need to focus on high risk abdominally obese patients. BMJ 2001; 322:716-720
2. International Day for the Evaluation of Abdominal obesity (IDEA). A study of waist circumference, cardiovascular disease and diabetes mellitus in 168,000 primary care patients in 63 countries. Circulation 2007; 116: 1942-1951
3.Â Yusuf PS, Hawken S, Ounpuu S, Dans T et al. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study):Case-control study. Lancet 2004; 364: 937-952
4. Pischon T, Boeing H, Hoffman K et al. General and abdominal adipocity and risk of death in Europe. New England Journal of Medicine 2008; 359: 2105-20.
5. Jacobs EJ, Newton CC, Wang Y, Patel AV et al. Waist Circumference and All-Cause Mortality in a Large US Cohort. Arch Int Med 2010; 170(15): 1293-1301
6. International Diabetes Federation (IDF). www.idf.org
7. Lemeiux I, Almeras N, Mauriege P, et al. Prevalence of "hypertriglyceridaemic waist" in men who participated in the Quebec Health Survey: association with atherogenic and diabetogenic metabolic risk factors. Can J Cardiol 2002; 18: 725-735
8. St-Pierre J, Lemieux I, Perron P, et al. Relations of the "hypertriglyceridaemic waist" phenotype to earlier manifestations of coronary heart disease in patients with glucose intolerance and type 2 diabetes. Am J Cardiol 2007; 99: 369-373
9. Czernichow A, Brickert E, Bertrais S, et al. Hypertriglyceridaemic waist and 7.5year prospective risk of cardiovascular disease in asymptomatic middle aged men. Int J Obes 2007; 31: 791-796