April 14, 2005 -- If you don't listen to your doctor, listen to your tailor.
By the time the tailor's tape says your waistline is larger than 39 inches, you may already be on the road to diabetes or heart disease. This holds true for both men and women, find Hans Wahrenberg, MD, and colleagues at Sweden's Karolinska Institute.
"This is like an alarm warning that you are going into the risk area," Wahrenberg tells WebMD.
Why? Wahrenberg's team finds that half of all men and women with waistlines of one meter or more -- that's 39.37 inches or more in the U.S. -- already have insulin resistance. But very few people with smaller waists have developed this dangerous condition.
Wahrenberg and colleagues report their findings in the April 15 Online First edition of the British Medical Journal.
Insulin Resistance: A Risk for Diabetes, Heart Disease
The cells in your body are powered by the sugar molecules called glucose. To keep this powerful fuel from flooding cells' engines, your body uses a hormone -- insulin -- to regulate glucose uptake. Insulin opens cells' gas caps so glucose can flow in.
But cells sometimes stop responding to insulin. This is what doctors call insulin resistance. When you have insulin resistance, your blood floods with glucose, which increases your risk for diabetes. It also fills it with other molecules that promote heart-clogging blood clots.
There are tests that gauge insulin resistance, but they are complicated, cannot be done in an office, and are usually reserved for research purposes. Now, Wahrenberg offers doctors and patients an easy rule of thumb for gauging who likely has insulin resistance.
The researchers looked at data from 2,746 "healthy" volunteers aged 18 to 72, whose waistlines ranged from 25.6 to 59 inches. All underwent complicated testing for insulin resistance.
"Insulin-resistance tests are positive in 50% of those who have a waist circumference above 1 meter [39.37 inches]," Wahrenberg says. "There are still obese people who are not insulin resistant. But if people have a waistline less than 1 meter, there is very little chance they are insulin resistant."
Earlier studies have suggested that insulin resistance can be predicted based on other clinical features. These features include body mass index (BMI), weight, hip circumference, and waist-to-hip ratio. But Wahrenberg says waist circumference alone predicts insulin resistance better than any of these other features alone or in combination.
"We are astonished waist circumference is so good a predictor," he says. "We had not expected it would have such good power."
The results also surprise Youfa Wang, MD, PhD, of the Center for Human Nutrition at the Bloomberg School of Public Health at Johns Hopkins University. Wang has studied ways to predict diabetes and heart disease.
"I am astonished," Wang tells WebMD. "It is quite encouraging that waist circumference is a very good predictor of insulin sensitivity and a good screening tool. It is very impressive that this can replace the other measures such as BMI as predictors."
Waist Under 39 Inches? Risks Remain for Many
Wang notes that insulin resistance isn't the real problem. The real problem is heart disease. And one reason why insulin resistance is so dangerous is that it's part of a group of risk factors called the metabolic syndrome. Those risk factors are high blood-fat levels (triglycerides), low levels of HDL "good" cholesterol, very high levels of LDL "bad" cholesterol, high blood pressure, excess body fat around the waist, and clotting abnormalities.
Though Wahrenberg finds that a 39-inch waistline is the cutoff for insulin resistance in both men and women, other dangerous factors may be brewing at smaller waistlines. This appears particularly true for women.
Wang's recent studies suggest that even these cutoffs may be too high. His work suggests that men already are at risk of heart disease and stroke when their waistlines reach 37.4 inches.