The numbers used to assess health are, for the most part, not helpful.
There are the vital signs: heart and respiratory rates and body temperature. Sometimes blood pressure. These are critical in emergencies. If you’ve been stabbed in the chest, paramedics want to know no numbers more than these.
But in day-to-day life, the normalcy of those numbers is expected. It doesn’t so much grant you a clean bill of health as indicate that you are not in acute danger. What if you just generally want to know whether you’re on pace to live an average life or longer?
The most common numbers are age and body weight. The U.S. health-care system places tremendous value on the latter, in the form of body-mass index, or BMI, a simple ratio of weight over height. BMI is used to define obesity and “overweight,” and so to stratify risks in insurance and health-care industries. This number has come to be massively consequential in the lives of millions of people, and to influence the movement of billions of dollars.