The study, published Wednesday in The Lancet Diabetes and Endocrinology and conducted by scientists at London School of Hygiene and Tropical Medicine, revealed that BMI that’s either too high or too low is tied to increased morbidity from a range of major diseases.
Krishnan Bhaskaran, lead author of the study and associate professor of statistical epidemiology, noted that his team found ‘important associations’ between BMI and most causes of death.
But people at the top and bottom ends of the BMI risked having shorter lives.
BMI is calculated by dividing an adult’s weight by the square of their height.
A ‘healthy’ BMI score ranges from 18.5 to 25.
Most doctors say it is the best method they have of working out whether someone is obese because it is accurate and simple to measure.
Obesity reduces life expectancy by 4.2 years in men and 3.5 years in women. Researchers also said that it can contribute to other chronic conditions, which include liver disease, diabetes and respiratory disease.
However, not everybody in the healthy category is at the lowest risk of disease, according to report author Dr Krishnan Bhaskaran.
Dr Bhaskaran said, “For most causes of death we found that there was an ‘optimal’ BMI level, with risk of death increasing both below and above that level.”
“At BMIs below 21, we observed more deaths from most causes, compared with the optimum BMI levels. However, this might partly reflect the fact that low body weight can be a marker of underlying ill-health.”
“For most causes of death, the bigger the weight difference, the bigger the association we observed with mortality risk.”
“So a weight difference of half a stone would make a relatively small (but real) difference; we could detect these small effects because this was a very large study.”
He nevertheless noted that the findings reiterated the importance of maintaining a BMI within the 21 to 25 range.
In particular, the results highlighted that the lowest risk of cardiovascular death was linked to a BMI of 25 kg/m2, with every additional 5 kg/m2 associated with a 29% increased risk of morbidity.