Every year that goes by brings more solid information suggesting that the body mass index (BMI) may become the future leading health indicator. If you’re wondering what BMI is; it’s your weight in kilograms (Kg) divided by the square of your height in meters (m2).  There’s solid evidence that BMIs in the upper 20s and higher are associated with a host of medical problems, many of them serious.  The main risks are increased mortality from cardiovascular disease and certain cancers, but also a host of other conditions like diabetes.

A new study published this month in the New England Journal of Medicine<http://www.nejm.org/doi/full/10.1056/NEJMoa1000367> looked at the bottom line, how increasing BMI results in death (in the epidemiology world called total mortality).  In the study researchers used a “reference group” of people with healthy BMIs (between 22.5 and 25) and compared them to people with higher and lower BMIs.  They found what you’d expect, that people with really low and really high BMIs had a higher risk of dying early.  Even being moderately overweight turns out to be a risk.  For example, BMIs between 25 and 30 had a 44% increased risk of death.  BMIs between 30 and 35 had an 88% increased risk of dying.  It gets worse after that.  BMIs between 40 and 50 were at almost 240% higher risk.  These percentages are based on the ”hazard ratios” that the researchers describe in the paper.  I’ve oversimplified in the paragraph above, so if you’re an epi, you better go straight to the source.

Their conclusion was that “overweight and obesity (and possibly underweight) are associated with increased all-cause mortality. All-cause mortality is generally lowest with a BMI of 20.0 to 24.9.”  Translation: try to maintain a healthy weight if you want to live longer.  There is an easy to use BMI calculator on the National Heart Lung and Blood Institute’s website.