Being overweight or underweight could knock up to four years off your life expectancy, research has suggested.
Scientists said that people who are over or underweight may be at greater risk of death than previously expected, with obesity knocking 4.2 years off life expectancy in men, and 3.5 in women.
The London School of Hygiene and Tropical Medicine, which led a peer-reviewed analysis of 3.6 million people and nearly 370,000 deaths, said while BMI – a measure of body fat – has long been a key indicator of health, its findings shine new light on the extent to which being over or under a certain BMI could lead to a shorter life expectancy.
BMI takes into account factors including age, weight and height to determine if someone is a healthy weight.
According to the study, published in The Lancet Diabetes and Endocrinology journal, BMI outside the healthy range of 21-25 was linked to several years of lost lifespan.
The report said the expected age of death for a 40-year-old of healthy weight who had never smoked was 82.2 years for men, and 84.3 for women.
Obesity was associated with knocking 4.2 years off that figure in men, and 3.5 years in women.
Class three obesity – those with a BMI of at least 40 – was associated with shortening life expectancy by 9.1 years in men and 7.7 years in women.
Those with a BMI of 21-25 were associated with the lowest risk of dying from cancer and heart disease.
The lowest risk of cancer death was with a BMI of 21 – with every 5-unit increase associated with a 13% higher risk.
The report found BMI was linked to death from every major cause – including cancer, cardiovascular disease, neurological issues and self-harm – except transport-related incidents.
Lead author, associate professor Krishnan Bhaskaran, said: “We know that BMI is linked to the risk of dying overall, but surprisingly little research has been conducted on the links to deaths from specific causes.
“We have filled this knowledge gap to help researchers, patients and doctors better understand how underweight and excess weight might be associated with diseases such as cancer, respiratory disease and liver disease.
“We found important associations between BMI and most causes of death examined, highlighting that body weight relative to height is linked to risk of a very wide range of conditions.
“Our work underlines that maintaining a BMI in the range 21-25 is linked to the lowest risk of dying from most diseases.”
Responding to the study, Dr Michelle McCully, head of research evidence and interpretation at World Cancer Research Fund, said: “Our research shows that overweight and obesity increases the risk of developing 12 cancers. Alongside our own research, this new study adds to the evidence that body weight influences both risk of, and survival from, cancer.
“WCRF calls on governments to take action in creating health-enabling environments that support people in following our cancer prevention recommendations, of which one is maintaining a healthy weight.”