Objective

Bioavailable insulin-like growth factor-I (IGF-I) interacts with obesity and exogenous estrogen (E) in a racial disparity in obesity-related cancer risk, yet their interconnected pathways are not fully characterized. We investigated whether circulating bioavailable IGF-I acted as a mediator of the racial disparity in obesity-related cancers such as breast and colorectal (CR) cancers and how obesity and E use regulate this relationship.

Methods

A total of 2,425 white and 164 African American (AA) postmenopausal women from the Women's Health Initiative Observational Study were followed from October 1, 1993 through August 29, 2014. To assess bioactive IGF-I as a mediator of race-cancer relationship, we used the Baron-Kenny method and quantitative estimation of the mediation effect.

Results

Compared with white women, AA women had higher IGF-I levels; their higher risk of CR cancer, after accounting for IGF-I, was no longer significant. IGF-I was associated with breast and CR cancers even after controlling for race. Among viscerally obese (waist/hip ratio >0.85) and overall nonobese women (body mass index <30), IGF-I was a strong mediator, reducing the racial disparity in both cancers by 30% and 60%, respectively. In E-only users and nonusers, IGF-I explained the racial disparity in CR cancer only modestly.

Conclusions

Bioavailable IGF-I is potentially important in racial disparities in obesity-related breast and CR cancer risk between postmenopausal AA and white women. Body fat distribution and E use may be part of the interconnected hormonal pathways related to racial difference in IGF-I levels and obesity-related cancer risk.

Introduction

Neighborhood environments may play a role in the rising prevalence of obesity among older adults. However, research on built environmental correlates of obesity in this age group is limited. The current study aimed to explore associations of Walk Score, a validated measure of neighborhood walkability, with BMI and waist circumference in a large, diverse sample of older women.

Methods

This study linked cross-sectional data on 6,526 older postmenopausal women from the Women's Health Initiative Long Life Study (2012-2013) to Walk Scores for each participant's address (collected in 2012). Linear and logistic regression models were used to estimate associations of BMI and waist circumference with continuous and categorical Walk Score measures. Secondary analyses examined whether these relationships could be explained by walking expenditure or total physical activity. All analyses were conducted in 2015.

Results

Higher Walk Score was not associated with BMI or overall obesity after adjustment for sociodemographic, medical, and lifestyle factors. However, participants in highly walkable areas had significantly lower odds of abdominal obesity (waist circumference >88 cm) as compared with those in less walkable locations. Observed associations between walkability and adiposity were partly explained by walking expenditure.

Conclusions

Findings suggest that neighborhood walkability is linked to abdominal adiposity, as measured by waist circumference, among older women and provide support for future longitudinal research on associations between Walk Score and adiposity in this population.