Associations between Neighborhood Walkability and Vitamin D in Overweight and Obese Women

Abstract

BACKGROUND: Vitamin D (VitD), a marker of bone health, is influenced by race, obesity, physical activity, and environment (i.e., sun exposure). Physical activity impacts both bone health and weight status. However, studies examining the association between neighborhood walkability and VitD are limited. PURPOSE: To investigate whether Walk Score (WSc), an indicator of neighborhood walkability, is associated with VitD in young overweight/obese women. METHODS: Project Health included 43 overweight/obese (body mass index, BMI ≥ 25 kg/m2) African American (AA) or Caucasian (C) women. Serum levels of 25-hydroxyvitamin D (VitD; ng/mL) were obtained via radioimmunoassay. WSc quantified the walkability of a person’s home address by analyzing walking routes to nearby destinations and amenities. Increased points assigned for amenities within a 5-min walk (0.25 miles) (WSc range=0-100). An ActiGraph GT3X+ accelerometer was used to estimate time (mins/day) in moderate-to-vigorous PA (MVPA; ≥760 counts per min; valid day and week defined as ≥8 hrs wear time on ≥3 days). T-test and χ2 were used to analyze race differences. General linear models examined the associations between WSc and VitD, and logistic regression determined the odds of having low VitD (<20 ng/mL) adjusting for MVPA, BMI and race. RESULTS: Women were 60% AA, mean age 27.0±4.6 years, mean WSc 61.1±26.7, and VitD levels of 24.1±12.6 ng/mL (AA: 19.4±7.8 ng/mL, C: 31.4±15.2 ng/mL, p=0.001). Low VitD was found in 40% of the total sample, with 58% in AA vs. 12% in C (p=0.003). A significant positive association was found between WSc and VitD (β=0.16, p=0.02), and a significant negative association between race and VitD (AA vs. C: β= −12.2, p=0.0009), while VitD had no association with MVPA (p=0.53) or BMI (p=0.16). For each 10 unit increase in WSc, there was a 54% reduced odds of women having low VitD levels (odds ratio, 95% confidence interval: 0.46, 0.25-0.73, p=0.005). CONCLUSIONS: WSc was positively associated with VitD, and higher WSc was associated with a decreased risk of low VitD in overweight/obese women. Neighborhood walkability may play an important role in VitD levels in overweight/obese women; however, more research is needed to determine the influences of race and possible mechanisms. Grant Support: Funded with an UMass Boston Proposal Development Grant.