BMI and Life Expectancy
People with a BMI of about 20 to 25 live the longest on average. Above 25, each 5 extra BMI points raised the death rate by about 31% in a study of 10.6 million adults. In our model, a BMI of 40 or more costs about 9 years for a 40-year-old man. Very low BMI also shortens life.
Work out your BMI
Then add it to the death clock calculator to see what it means for your own estimate.
What did the Global BMI Mortality Collaboration find?
This is the largest study of BMI and death. It pooled data from 239 studies in four continents, covering more than 10 million adults, and was published in The Lancet in 2016. To avoid bias, the main analysis only used never-smokers without major illness at the start, and left out deaths in the first five years.
- The lowest death rates were at a BMI of about 20 to 25.
- Above 25, risk rose steadily: about 31% higher for every 5 BMI points.
- The link was found in Europe, North America, East Asia and Australia and New Zealand.
- The extra risk from high BMI was bigger in younger adults and in men.
How many years does each BMI band cost?
| BMI band | Hazard ratio used | Men: change in years | Women: change in years |
|---|---|---|---|
| Under 18.5 | 1.51 | -3.8 | -3.9 |
| 18.5 to 19.9 | 1.13 | -1.1 | -1.2 |
| 20 to 24.9 | 1.00 | reference | reference |
| 25 to 27.4 | 1.07 | -0.6 | -0.6 |
| 27.5 to 29.9 | 1.20 | -1.7 | -1.7 |
| 30 to 34.9 | 1.45 | -3.4 | -3.5 |
| 35 to 39.9 | 1.94 | -6.1 | -6.3 |
| 40 or more | 2.76 | -9.2 | -9.5 |
These are model figures, converted from the study’s hazard ratios. A hazard ratio of 1.45 means a 45% higher death rate at every age.
Why are Asian BMI cut-offs lower?
At the same BMI, people of South Asian, East Asian and Southeast Asian origin tend to have more body fat and a higher risk of type 2 diabetes and heart disease. A WHO expert consultation in 2004 suggested extra action points at a BMI of 23 and 27.5 for Asian populations. Many health bodies in India, Pakistan, China and Singapore use lower cut-offs. Tick the Asian option in the BMI tool above to see your band on that scale. More detail is on what is BMI in death clock.
Is BMI a good measure?
It is a quick, useful screen, not a diagnosis. BMI can’t tell muscle from fat, so very muscular people can score high while being healthy. Waist size adds useful information: a larger waist signals more fat around the organs, which carries more risk. A doctor can look at your full picture.
Frequently asked questions
What BMI lives the longest?
In the Global BMI Mortality Collaboration study, the lowest death rates were at a BMI of about 20 to 25 among never-smokers without major illness.
How much does obesity shorten life?
In our model, based on the study’s hazard ratios, a BMI of 30 to 34.9 costs about 3 years for a 40-year-old UK man, and a BMI of 40 or more about 9 years.
Is being underweight bad for life expectancy?
Yes. A BMI under 18.5 had a 51% higher death rate than the reference group in the same study. Sometimes low weight is a sign of illness, so it is worth checking with a doctor.
Is BMI accurate for muscular people?
Not always. BMI can’t tell muscle from fat, so very muscular people can have a high BMI and still be healthy. Waist size is a useful extra check.
Sources
- Global BMI Mortality Collaboration. Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. The Lancet, 2016; 388: 776-786. doi.org/10.1016/S0140-6736(16)30175-1
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 2004; 363: 157-163. doi.org/10.1016/S0140-6736(03)15268-3
Compare with the effect of smoking on smoking and life expectancy, or run the full death clock.