Is body mass index associated with lowest mortality increasing over time?

Area of Science:

• Public Health
• Epidemiology
• Biostatistics

Background:

• Debate exists on whether the body mass index (BMI) associated with lowest all-cause mortality has changed over time.
• Such changes could necessitate revisions to World Health Organization (WHO) BMI categories for normal weight and overweight.
• This study investigates trends in BMI associated with lowest mortality in US adults.

Purpose of the Study:

• To assess if the body mass index (BMI) linked to the lowest all-cause mortality has increased over time in US adults.
• To evaluate the implications for current BMI classification systems.

Main Methods:

• Analysis of the National Health Interview Survey (NHIS) data with up to 25 years of follow-up.
• Inclusion of 901,197 participants (aged 20-79) with baseline BMI 18.5–39.9 kg/m².
• Estimation of BMI associated with lowest mortality across different survey periods (1986-2009) and fixed follow-up durations (5-20 years).

Main Results:

• A U-shaped BMI-mortality association was observed across all periods.
• Using original follow-up durations, BMI for lowest mortality increased from 23.9 kg/m² (1986-1989) to 28.6 kg/m² (2005-2009).
• However, with fixed follow-up durations (especially 15 years), BMI for lowest mortality showed stability over time, even in specific subgroups.

Conclusions:

• The body mass index (BMI) associated with the lowest all-cause mortality remains relatively stable over time when a fixed long-term follow-up duration is applied.
• Findings suggest that current BMI categories may not require revision based on temporal trends in mortality risk.