September 14, 2025

expert reaction to unpublished conference abstract and poster looking at the association between Body Mass Index and mortality

An unpublished conference abstract presented at the European Association for the Study of Diabetes (EASD) in Vienna looks at the association between Body Mass Index and mortality.

Dr Baptiste Leurent, Associate Professor in Medical Statistics, UCL, said:

“This study is only reported as a short conference abstract and poster, and it is not possible to assess its validity.  It is too premature to be safely shared with the public, and some parts (particularly the title) of the press release are misleading.

“The plot on the poster is the most interesting summary of the findings, and confirms a commonly seen U-shape association between BMI and mortality.

“It is correct to say that the very low end of the normal BMI range (18.5-20 kg/m²) had a higher mortality than the other normal or overweight population, which is interesting but possibly expected given the known U-Shape association.

“However, stating that there is no higher risk in the obese population is misleading.  The lower end of the obese group (BMI 30 to 35 kg/m2) still had a up to 14% higher mortality rate.  This is far less than the higher BMI groups, but should not be considered negligible.

“While the study indeed found no higher mortality rate in the overweight, it is not clear if this applies to obese person (BMI above 30), even in the lower end of the range.

“Although the study controlled for a few factors one should be careful not to interpret this as a causal link between weight and mortality, as could be suggested by the title.

“The choice of adjustment factors is also debatable.  People with higher BMI are likely to have more co-morbidities, which could result in higher risk of death caused by elevated BMI.  Removing this effect from the comparison is likely to distort the causal association between BMI and mortality.

“The data come from ‘persons with Dual-Energy X-Ray Absorptiometry (DXA)-scans’, it is not clear how representative this is of the general population.  If people in poorer health or overweight are more likely to attend these scans, it could then distort the association.

“Overall, the association between BMI and mortality is complex.  This study adds some further evidence about its U-shape association and that the ‘healthiest’ weight might be higher that often considered.  But there is not enough information available and this has not been peer-reviewed.  In my opinion it is premature for these results to be highlighted to the public at this stage before peer review as there is a risk they could be misinterpreted.

“We look forward to seeing the complete research when published.”

Prof John Wilding, Professor of Medicine, Department of Cardiovascular and Metabolic Medicine, University of Liverpool, said:

“This is a relatively small study compared to much larger international cohort studies that also show u shaped curve, but much stronger relationships between high BMI and mortality.

“Two really important additional points are:

“1. That the population studied are people having DEXA Scans for bone mineral density so likely does not reflect wider Danish population.  DEXA scans are more likely to done in people who have had bone fractures, so may overrepresent older people with frailty.

“2. The much higher mortality in low BMI may well be due to reverse causality i.e. people who are sick for other reasons (e.g. heart failure, cancer etc), may be losing weight even if undiagnosed at the time of study.

“Hence without more detail about methods and population studied, I don’t think this study will change the current evidence supporting the consensus that obesity, and particularly severe obesity is associated with increased mortality.”

Abstract title: ‘The association between Body Mass Index and mortality: A cohort study’ by Sigrid Bjerge Gribsholt et al. It was presented at the European Association for the Study of Diabetes (EASD) in Vienna, and was under embargo until 23:01 UK time on Sunday 14 September 2025.

There is no paper.

Declared interests

Dr Baptiste Leurent: “No conflict of interest.”

Prof John Wilding: “John Wilding reports consultancy / advisory board work for the pharmaceutical industry contracted via the University of Liverpool in the last 36 months (no personal payment) for Alnylam, Amgen, AstraZeneca, Boehringer Ingelheim, Cytoki, Kailera, Lilly, Menarini, Metsera, Napp, Novo Nordisk, Pfizer, Prosciento, Response Pharmaceuticals, Rhythm Pharmaceuticals, Saniona, Shionogi and Ysopia; funding for clinical trials from Amgen, AstraZeneca and Novo Nordisk and personal honoraria / lecture fees from AstraZeneca, Boehringer Ingelheim, Medscape, Novo Nordisk and Menarini.

He is past president of the World Obesity Federation, a member of the Association for the Study of Obesity, Diabetes UK, EASD, ADA, Society for Endocrinology and the Rank Prize Funds Nutrition Committee.  From 2009-2024 he was national lead for the Metabolic and Endocrine Speciality Group of the UK NIHR Clinical Research Network.”