Aust Crit Care. 2025 Nov 24;39(1):101461. doi: 10.1016/j.aucc.2025.101461. Online ahead of print.
BACKGROUND: An increased body mass index (BMI) is associated with improved outcomes in intensive care unit patients, known as the «obesity paradox».
OBJECTIVE: The objective of this study was to investigate whether sex and age modify the obesity paradox.
METHODS: We performed a retrospective, multicentre, observational study of a binational registry. All patients with a recorded BMI admitted to the intensive care unit in Australia and New Zealand between 2010 and 2022 were included in the study cohort. The primary outcome was in-hospital mortality. Using multivariable models, we analysed the impact of sex and age on the relationship between BMI and outcome.
RESULTS: We studied 957 873 patients (565 759 men and 392 114 women; median BMI: 27.8 kg/m2 for both groups). For both groups, an increased BMI was associated improved survival, for a BMI up to >35 kg/m2. However, this protective association was modified by sex. At a BMI of 30 kg/m2, compared to a baseline BMI of 22.5 kg/m2, an odds ratio (OR) (95% confidence interval [CI]) of 0.83 (0.81-0.87) was estimated for men and 0.93 (0.89-0.98) for women, implying a stronger association for men. Furthermore, the paradox was also modified by age with a more pronounced effect for older patients. For men, the OR of 0.89 (0.82-0.98) at a BMI of 30 kg/m2 and age of 40 years reduces to 0.80 (0.76-0.84) at the same BMI and an age of 75 years. For women, the OR of 0.99 (0.92-1.13) at a BMI of 30 kg/m2 and age of 40 years reduces to 0.89 (0.84-0.93) at the same BMI and an age of 75 years.
CONCLUSION: The obesity paradox is modified by both sex and age. The paradox is more pronounced for men and within the group of older patients.
PubMed:41289706 | DOI:10.1016/j.aucc.2025.101461