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.

Adapted from BMJ 2001; 322: 716-720. Reproduced with permission from the BMJ Publishing Group.

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 and EPIC, 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%)

Age and region adjusted frequencies of CVD and diabetes across gender-specific quintiles of waist circumference in the overall IDEA study population of (A) men (n=69,409) and (B) women (n=98,750)

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)

Frequency of known CVD for men (A) and women (B), and known diabetes for men (C) and women (D), adjusted for age, region, and smoking status, by gender specific waist circumference tertiles and BMI categories. The percentage of patients in each of the 9 groups on each graph is shown

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.

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 ethnicity⁵.

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"⁶. 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 disease^7,8 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.

References