Being “overweight” is associated with lowest mortality rate

Change in Body Mass Index Associated With Lowest Mortality in Denmark, 1976-2013

Shoaib Afzal, Anne Tybjærg-Hansen, Gorm B. Jensen and Børge G. Nordestgaard, 2016 – full study

What’s it about?

Having a BMI which falls into the “normal” category (between 18.5 to 24.9) is generally considered to be best for our health. These researchers were considering which BMI category is optimum in terms of mortality.

Who took part?

120, 548 participants were recruited from three national Danish Studies:

  • Copenhagen City Heart Study 1976-1978 (n = 13 704)
  • Copenhagen City Heart Study 1991-1994 (n = 9482)
  • Copenhagen General Population Study in 2003-2013 (n = 97 362)

All participants were followed up from inclusion in the studies to November 2014, emigration, or death, whichever came first.

How was this studied?

BMI, waist circumference and waist-hip ratio were measured.

Participants filled in a questionnaire on smoking status (never, former, or current), tobacco consumption (number of cigarettes per day), alcohol consumption, intensity of leisure-time physical activity during a week, and level of income.

History of cardiovascular disease and cancer (excluding non-melanoma skin cancer) was also recorded.

Date and cause of deaths during the study were collected from the Danish Civil Registration System and Danish Causes of Death Registry.

What was found?

Low and High BMI were associated with highest all-cause mortality – people classified as “normal weight” (BMI from 18.5 to 24.9) or “obese” (BMI of 30 or greater) had the same risk.

Mortality risk did not increase with weight – the findings actually formed a U-shaped graph. Risk decreased until BMI of 27.0, and then increased again.

The BMI associated with lowest cancer mortality risk could not be determined.

The BMI associated with lowest all-cause mortality has increased:

  • 23.7 in 1976-1978
  • 24.6 in 1991-1994
  • 27.0 in 2003-2013

The risk of all-cause mortality for “overweight” (BMI of 25 to 29.9) and “obese” (BMI of 30 or greater) people has reduced from 1976-1978 through 1991-1994 to 2003-2013.

The bottom line:

The BMI associated with least risk of death has increased, and now falls into the “overweight” category. This study highlights that there is not a linear relationship between BMI and mortality. It also suggests that within the population, the average BMI of healthy people is increasing.

Overall, these findings challenge the belief that a having a “normal” BMI is optimum or necessary for our health.