Abstract
Insufficient physical activity (IPA) affects over 50% of Iranian adults and is a modifiable risk factor for diabetes mellitus (DM). This study estimates the population attributable fraction (PAF) of DM associated with domain-specific IPA in Iran. This cross-sectional study analyzed Iran STEPs 2021 data from 18,013 adults aged ≥ 18 years. IPA was defined as < 600 MET-minutes/week in leisure-time or walking domains using GPAQ-2. Age- and sex-specific PAFs were calculated using Miettinen's formula with external relative risks from meta-analyses. Domain-specific PAFs are non-additive. DM prevalence was higher among adults with leisure-time IPA versus active peers (19.6% vs. 10.5%, p < 0.001) and among those with walking inactivity versus active peers (18.8% vs. 17.9%, p = 0.017). Using external relative risks, 14.6% (95% CI 11.5, 17.6) of DM cases were associated with leisure-time IPA and 15.7% (95% CI 12.4, 18.9) with walking inactivity. The internal age-sex adjusted odds ratio for walking inactivity was 1.11 (95% CI 1.02, 1.21). Women had higher PAFs than men (leisure-time: 15.0% vs. 14.1%; walking: 16.4% vs. 14.6%). Leisure-time IPA prevalence exceeded 95% among adults with no formal education, women, and older adults. Approximately 50% of individuals with DM remained untreated. Under causal assumptions, approximately 15% of DM cases in Iran were associated with IPA. If these associations reflect modifiable causal relationships, increasing physical activity particularly leisure-time activity could lower diabetes prevalence. However, near-universal inactivity in several subgroups suggests activity promotion should be embedded within comprehensive strategies addressing obesity, diet, and healthcare access. These estimates are hypothetical impact fractions, not precise predictions of preventable cases.