Association among length of residence, physical activity, and obesity in the US immigrants: A regression-based mediation analysis.

Objectives: To examine the mediated relationship between objectively measured obesity, accelerometer-based moderate-to-vigorous physical activity (MVPA), and length of residence among US immigrants.

Methods: A total of 885 adults (≥18 years) who were born outside the United States from the 2003 to 2006 National Health and Nutrition Examination Survey were included in the analysis. The participants were categorized into two groups (i.e., living in the United States ≥15 years vs. <15 years). MVPA time (minutes/day) was measured by ActiGraph accelerometry. Obesity was defined as body fat percentage measured by dual-energy X-ray absorptiometry. Regression-based mediation analysis was conducted using SURVEY procedures in SAS version 9.4.

Results: When controlling for covariates, immigrants living in the United States for ≥15 years were significantly less likely to spend time participating in MVPA (c; β = -4.50, p = .04), and more likely to be at high risk of obesity (a; β = 1.70, p = .01) compared to those living in the United States for <15 years. Also, the relationship between obesity and MVPA was statistically significant (b; β = -0.80, p = .003). Length of residence was indirectly associated with MVPA (ab; β = -1.37, p = .03), suggesting that obesity mediated the association of length of residence on MVPA (c'; β = -3.13, p = .20).

Conclusions: Obesity mediated the association between length of residence and MVPA in the US immigrants. These findings may encourage long-term US immigrants to prevent and treat obesity for increasing the amount of MVPA time.