Vitamin D Sub-set Analysis from the Flash Study

Author

Megan Bishop, California Polytechnic State University, San Luis ObispoFollow
Laura Hall, California Polytechnic State University - San Luis ObispoFollow
Ann McDermott, California Polytechnic State University - San Luis ObispoFollow
Aydin Nazmi, California Polytechnic State University - San Luis ObispoFollow

DOI: https://doi.org/10.15368/theses.2012.17
Available at: https://digitalcommons.calpoly.edu/theses/700

Date of Award

3-2012

Degree Name

MS in Agriculture - Food Science and Nutrition

Department/Program

Food Science and Nutrition

Advisor

Laura Marie Hall

Abstract

Vitamin D is important to the health of college students. The objective of our study was to measure sun exposure, skin pigmentation, vitamin D intake, and serum 25-hydroxyvitamin D (25[OH]D) in a subset of participants from The Following the Longitudinal Aspects of Student Health (FLASH) Study to determine the best predictors of 25(OH)D status. Participants were college-aged freshman who had their blood drawn in spring (Visit 1) and fall 2010 (Visit 2) at California Polytechnic State University (Cal Poly), San Luis Obispo, CA. (35.3°N). Vitamin D intake was measured using a 28-day food frequency recall questionnaire (specific to vitamin D foods and supplements) while questions specific to the frequency of milk and fish intake were accessed from the FLASH questionnaire. Sun exposure was measured using a 28-day recall questionnaire (time in sun and sun exposure index [SEI]) and questions (frequency of weekday/ weekend exposure) from the FLASH questionnaire. Skin pigmentation was measured using a reflectance spectrophotometer. Serum 25(OH)D was measured at a local pathology lab as measured by an IDS-iSYS. Means (SD) were as follows (n= 40): reflectance of the forehead was 61 (3.5) L* (Lightness) for Visit 1 and 61 (4.3) L* for Visit 2. Vitamin D intake was 308 (234) IU for Visit 1 and 316 (257) IU for Visit 2. Time outside was 81 (44) mins for Visit 1 and 76 (39) mins for Visit 2. Serum 25(OH)D was 85 (24) nmol/L for Visit 1 and 113 (28) nmol/L in Visit 2 which was significantly higher (p < 0.0001). The SEI was 53 (38) body surface area (BSA) exposed (m²) x mins for Visit 1 and 55 (34) m² x mins Visit 2. Although 90% of participants in Visit 1 and 88% in Visit 2 were below the RDA guidelines for vitamin D intake (600 IU/day), 5% of participants in Visit 1 and none in Visit 2 had serum 25(OH)D serum levels < 50 nmol/L (the recommended level of sufficiency for bone health), demonstrating the importance of sun exposure to vitamin D status in these college students. To determine the strongest predictors of status we used regression analysis to predict serum 25(OH)D with skin reflectance, vitamin D intake, and sun exposure. We found that weekend sun exposure, fish intake, and forehead skin reflectance were the strongest predictors of serum 25(OH)D (R²= 0.50, p= 0.0010) demonstrating that simple questionnaires can help to predict serum 25(OH)D status.