The obesity paradox in the US population

Area of Science:

• Epidemiology
• Public Health
• Biostatistics

Background:

• Recent studies indicate a paradoxical lower mortality risk for obese individuals compared to normal-weight individuals.
• The underlying reasons for this obesity paradox remain largely unidentified.

Purpose of the Study:

• To investigate the existence of the obesity paradox within the US population.
• To determine if reverse causation could explain the observed paradoxical mortality patterns.

Main Methods:

• Survival analyses were conducted using data from 35,673 participants across three National Health and Nutrition Examination Survey (NHANES) waves (I, II, and III).
• The study calculated the relative risk (RR) of all-cause mortality associated with obesity over three distinct 15-year follow-up periods.
• A total of 7087 deaths were recorded during the follow-up intervals.

Main Results:

• A lower relative mortality risk for obesity was observed exclusively in the NHANES III cohort and specifically among men with diverse, serious pre-existing illnesses.
• For this subgroup, relative mortality risks were 2.22 (NHANES I), 0.89 (NHANES II), and 0.65 (NHANES III).
• Mortality rates for seriously ill normal-weight men remained stable, while those for seriously ill obese men significantly decreased, indicating reverse causation was unlikely.

Conclusions:

• The obesity paradox, characterized by lower mortality risk in obese individuals, was identified only in NHANES III among severely ill men.
• Reverse causation does not appear to be a significant factor explaining this specific finding.
• Further research is necessary to validate these conclusions.