Why BMI Isn't An Accurate Measurement Of Individual Health
As of today, if you are 16 years of age or older in Wisconsin, you are eligible to get a COVID-19 vaccine. This step of opening enrollment comes ahead of schedule but previous to this date, one of the qualifications that could get you a vaccine was a BMI, or body mass index, of 25 or higher.
This BMI range is categorized as overweight and 30 or above is considered obese. This qualification made almost 70% of Wisconsinites eligible, but it also brought up a lot of questions of how we measure health, as well as body weight issues for some.
BMI, however, wasn't created as a measurement of health — but curiosity, Paula Papanek says. She's Marquette University's director of exercise science.
"It was developed without really any clinical or physiology or medical reasons behind it. It was developed in the 1830s by [Adolphe Quetelet], a sociologist who was also a mathematician and basically a stats guy. And at the time, he called it 'social physics' and he was describing what the shape of normal men were in Belgium," she explains.
Papanek notes this system of measurement wasn't given the name "BMI" until 1972. Prior to that, height and weight charts provided by the Metropolitan Life Insurance Company in the United States were used to describe the population. By the 1980s, BMI was used, she says.
"The formula to calculate BMI, weight divided by height in meters squared, is the same all over the world," Papanek explains. And there's also no differences between men and women calculations — even today.
|Normal/Healthy Weight:||18.5 - 24.9|
|Overweight:||25 - 29.9|
|Obese:||30 and above|
BMI does not differentiate between fat and muscle, and it is not especially accurate if you are either very short or very tall, she says. Even most athletes would be considered obese on a medical chart or insurance record because dense muscle weight often categorizes them as having abnormally high BMIs.
Instead of potentially being alarmed by the category you fall under, Papanek says to think of BMI as a tool to find trends in large populations, not necessarily individuals.
What BMI really is is a screening tool. It doesn’t directly measure anything about a disease or your health. It’s used to warn people because of relationships that we have seen with BMI and other diseases.
"What BMI really is is a screening tool," she notes. "It doesn’t directly measure anything about a disease or your health. It’s used to warn people because of relationships that we have seen with BMI and other diseases."
For example high blood sugar or blood pressure are specific measurements of health, and a higher BMI is often associated with an increased risk of lots of diseases. Overall, BMI is not causal but relational, according to Papanek.
There are also better ways to measure individual health than BMI, she says.
"A waist to hip ratio, measuring how big your belly is, knowing where that fat is carried would be a much better risk factor for all these conditions that we're talking about, absolutely," says Papanek. "But they're not easy and they're definitely not something that can be scaled up and not require a trained technician in order to do it."
So why use BMI for vaccine distribution? Because it's simple, non-invasive and can encompass a large population, she says.
"Thirty percent of COVID hospitalizations were attributed to obesity, so it makes sense to target this population," says Papanek. "Remember that if we had all the vaccine in the world, we wouldn't have to create criteria for people to get in line, but we don't. ... So we needed an easy, understandable qualification — something that was objective. Because we know that BMI and the risks of [severe] COVID is very real, it was the next logical choice."
So overall, take your BMI with a grain of salt.
"What we know about BMI is that if you're in the extremes, we're overestimating or underestimating. You have to look at that data and the individual," says Papanek.
Words and labels associated with someone's weight can cause harm, and forcing people struggling with eating disorders or body dysmorphia to look at their BMI can be traumatic. There are also circumstances in which BMI can be misused, especially if it's needed for insurance. Papanek recommends that if you need a more accurate measurement of your physiology, go to a research laboratory or ask your physician for a more effective way to measure your health.