**Background:** Physical activity is known to reduce chronic disease risk, but most evidence on step counts and mortality comes from older urban populations. American Indian individuals have a higher burden of chronic disease and premature death than the general US population, yet no studies had examined the association between objectively measured ambulatory activity and mortality in this group. Walking is the most common form of physical activity in many American Indian communities, making steps per day a relevant and easily communicated metric.
**Methods:** This study used data from the Strong Heart Family Study (SHFS), an ongoing population-based longitudinal cohort of American Indian individuals from 12 communities in Arizona, North Dakota, South Dakota, and Oklahoma. The analytic sample included 2,204 participants aged 14–65 years who completed a baseline examination (2001–2003) with at least 3 days of valid pedometer data (AE120 Accusplit pedometer). Participants wore the pedometer on their hip during waking hours for 7 consecutive days and recorded daily steps in a diary. Deaths were adjudicated through December 31, 2020, via medical records, death certificates, the National Death Index, and other sources. Mixed-effects Cox proportional hazards regression (clustered on family) was used to estimate hazard ratios for mortality. Three models were fit: Model 1 adjusted for age, sex, and study site; Model 2 additionally adjusted for education, smoking, alcohol use, and diet quality; Model 3 further adjusted for BMI, systolic blood pressure, prevalent diabetes, prevalent CVD, biomarkers (fibrinogen, LDL cholesterol, triglycerides), medication use, and self-reported health status. Multiple imputation addressed <3% missing covariate data.
**Key Results:** The mean (SD) age was 41.0 (16.8) years; 59.9% were female; mean BMI was 31.2 (7.4). Median steps per day was 5,085 (mean 5,841). Only 12.2% of participants accumulated ≥10,000 steps/d, and 69.8% accumulated <7,000 steps/d. During a mean 17.0-year follow-up (range 0–19.9 years), there were 449 deaths, including 123 from CVD. In the fully adjusted model (Model 3), participants in the upper three quartiles of steps per day had significantly lower risk of death compared with the lowest quartile (<3,126 steps/d): Q2 (3,126–5,085 steps/d): HR 0.72 (95% CI, 0.54–0.95); Q3 (5,086–7,572 steps/d): HR 0.66 (95% CI, 0.47–0.93); Q4 (≥7,573 steps/d): HR 0.65 (95% CI, 0.44–0.95). This corresponds to a 28%–35% lower risk of death. Cubic spline models showed a nonlinear inverse association, with risk plateauing at higher step counts. Results for CVD mortality were similar but with wider confidence intervals (e.g., Q4 vs. Q1: HR 0.78; 95% CI, 0.42–1.46 in Model 3). No significant interactions were found by age (P=0.21), sex (P=0.32), study site (P=0.32), BMI (P=0.36), or diabetes status (P=0.91). Sensitivity analyses excluding early deaths (first 2 years), excluding participants with fair/poor health or CVD, and omitting minimum/maximum step days did not materially alter results.
**Clinical Implications:** This study provides the first evidence linking objectively measured ambulatory activity to mortality in American Indian individuals, a population with high CVD risk and lower life expectancy. The finding that benefit was observed at a threshold as low as ~3,126 steps/d—far below the commonly cited 10,000 steps/d goal—is particularly important for this largely inactive rural population (median 5,085 steps/d). The results suggest that public health messaging should emphasize that even modest increases in daily walking may reduce mortality risk. Step counters are inexpensive tools that could support physical activity outreach programs targeting inactive individuals. However, the observational design cannot fully exclude residual confounding or reverse causation, and the low activity threshold observed may reflect the high baseline morbidity in this population rather than a true biological threshold.