Vitamin D–binding protein modifies the vitamin D–bone mineral density relationship

Studies examining the relationship between total circulating 25‐hydroxyvitamin D [25(OH)D] levels and bone mineral density (BMD) have yielded mixed results. Vitamin D–binding protein (DBP), the major carrier protein for 25(OH)D, may alter the biologic activity of circulating vitamin D. We hypothesized that free and bioavailable 25(OH)D, calculated from total 25(OH)D, DBP, and serum albumin levels, would be more strongly associated with BMD than levels of total 25(OH)D. We measured total 25(OH)D, DBP, and serum albumin levels in 49 healthy young adults enrolled in the Metabolic Abnormalities in College‐Aged Students (MACS) study. Lumbar spine BMD was measured in all subjects using dual‐energy X‐ray absorptiometry. Clinical, diet, and laboratory information also was gathered at this time. We determined free and bioavailable (free + albumin‐bound) 25(OH)D using previously validated formulas and examined their associations with BMD. BMD was not associated with total 25(OH)D levels (r = 0.172, p = .236). In contrast, free and bioavailable 25(OH)D levels were positively correlated with BMD (r = 0.413, p = .003 for free, r = 0.441, p = .002 for bioavailable). Bioavailable 25(OH)D levels remained independently associated with BMD in multivariate regression models adjusting for age, sex, body mass index, and race (p = .03). It is concluded that free and bioavailable 25(OH)D are more strongly correlated with BMD than total 25(OH)D. These findings have important implications for vitamin D supplementation in vitamin D–deficient states. Future studies should continue to explore the relationship between free and bioavailable 25(OH)D and health outcomes. © 2011 American Society for Bone and Mineral Research.     

Building Relationships and Capacity in Rural Lunchrooms: Lessons from a Process Evaluation of a Pilot Behavioral Economics-Based Intervention

We aimed to describe the successes and challenges of implementing a pilot program by working with students and food service staff in four rural high schools to encourage healthy eating among rural adolescents. The pilot program engaged students and school food service directors (FSDs) in identifying and making changes to the school lunchroom environment based on behavioral economics. As part of a multi-method evaluation, we conducted interviews with FSDs and staff, held focus groups with students, and recorded our observations as researchers. The lessons learned highlighted the importance of (1) the FSD’s role in the school, (2) a faculty partner involved in the project, (3) the characteristics of the student group, and (4) setting realistic goals for the students. Our findings can guide future interventions designed to improve food choices in school lunchrooms and increase adolescents’ fruit and vegetable consumption.