One Clear Value for BMI: Ticket to a Vaccine

BMI stinks. That’s the lead on a lot of stories about how to get a COVID-19 vaccine appointment right now. This is a perfect example of mixed messaging. But it also reflects our very mixed feelings about this measure that’s now almost two centuries old. A BMI of 30 is the threshold for a population-based designation of obesity. It’s not a diagnosis, but in many places, it is a ticket to getting the COVID-19 vaccine right now.

Pretty Average

Here’s a basic fact. A BMI of 30 is pretty average in the U.S. An average man is five feet and nine inches tall and weighs 199.8 pounds. That equals a BMI of 29.5. For an average woman, the numbers are five feet, three and a half inches, 170.8 pounds, and a BMI of 29.8.

Yet if someone wants to get the vaccine, odds are good that they will take umbrage at any suggestion that BMI might qualify them. “That’s a rude thing to say,” would be the retort. And of course that’s right. A person’s body size is not fair game for polite conversations. Thus we have the problem of BMI hesitancy – people with a BMI over 30 who doubt that they are qualified to get a vaccine appointment.

Yes, BMI Has Flaws

BMI definitely has flaws. It’s very useful for population-based studies of metabolic health and obesity. But it is not a measure of individual health. Rather, it is simple number that offers a crude yardstick for adiposity. Fourteen-year-old Tessa Embry explained it well in 2016 when she pushed back on a teacher who wanted to know her BMI as part of a health lesson. She wrote an essay, which says in part:

“One of the formula’s obvious flaws… is that it has absolutely no way of discriminating fat and muscle.

“BMI is an outdated way of determining a person’s body health, and it’s a measurement that should not be used in a school setting where students are already self-conscious and lacking confidence in their unique bodies.

“My BMI is none of your concern because my body and BMI are perfect and beautiful just the way they are.”

Note that she based these statements on a thoughtful conversation with her personal physician about her health and weight status.

But the Biggest Flaw Is Human Bias

Still, despite its limitations, BMI is a useful screening tool. And for COVID-19, it is a good indicator of risk and thus who should go first for a vaccine based on medical risk. The only better predictor of risk is age.

The real reason we have such mixed feelings about BMI as a ticket to a vaccine appointment is because we are so mixed up and biased about obesity. Even smart people (like the AHA) treat BMI as a mark of unhealthy behavior, not a simple screen for body composition.

Thus they promote implicit weight stigma and stigmatize obesity. So if obesity is the ticket to a vaccine appointment, some people will hesitate. Obesity is a medical condition, not a choice. BMI is just a number. But a COVID vaccine can be life-saving. Take it as soon as you can.

Click here, here, and here for more on BMI and the COVID-19 vaccine. For an excellent new analysis of BMI and mortality risk, click here.

30, photograph © Andreas Levers / flickr

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March 19, 2021