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. 2019 May 27;3(7):nzz065.
doi: 10.1093/cdn/nzz065. eCollection 2019 Jul.

Circulating 25-Hydroxyvitamin D Concentrations in Overweight and Obese Adults Are Explained by Sun Exposure, Skin Reflectance, and Body Composition

Brian D Piccolo  1   2 , Laura M Hall  3 , Charles B Stephensen  3   4 , Erik R Gertz  4 , Marta D Van Loan  3   4
Affiliations

Circulating 25-Hydroxyvitamin D Concentrations in Overweight and Obese Adults Are Explained by Sun Exposure, Skin Reflectance, and Body Composition

Brian D Piccolo et al. Curr Dev Nutr. .

Abstract

Background: Obese individuals are known to be at higher risk for vitamin D deficiency than normal-weight individuals. Cutaneous synthesis is a major source of vitamin D; however, objective measurements of sun exposure are lacking in this population.

Objective: To assess the validity of a regression model using sun exposure in lean individuals to estimate serum 25-hydroxyvitamin D [25(OH)D] in overweight and obese individuals, and to develop a prediction equation for serum 25(OH)D in overweight and obese adults.

Methods: This study was a secondary analysis of a 15-wk controlled feeding study investigating the effects of dairy consumption on body composition. Information regarding sun exposure, including day, hour, time outside, and clothing, were self-assessed in sun exposure diaries. Personal sun exposure energy (joules) was assessed by downloading time-specific ultraviolet B energy data from climate stations. Skin reflectance was measured using a Minolta 2500d spectrophotometer. Dietary intake of vitamin D was known. Serum 25(OH)D concentration was measured by radioimmunoassay. Body composition was determined from whole-body dual energy x-ray absorptiometry and computed tomography scans.

Results: Sun exposure was positively related to serum 25(OH)D (r = 0.26; P ≤ 0.05) and inversely related to total fat mass, android fat, and BMI (r = -0.25, -0.30, and -0.32, respectively). The modified Hall model significantly overestimated serum 25(OH)D in overweight and obese adults by 27.33-80.98 nmol/L, depending on the sun exposure calculation. A new regression model was developed for overweight and obese persons that explained 29.1% of the variance in postintervention 25(OH)D concentrations and included sun exposure, skin reflectance, total fat mass, total lean mass, and intra-abdominal adipose tissue as predictors.

Conclusion: Major determinants of serum 25(OH)D concentration in healthy overweight and obese individuals include sun exposure, skin reflectance, and adiposity. Addition of adiposity terms to the prior model significantly improved predictive ability in overweight and obese men and women. (clinicaltrials.gov: NCT00858312).

Keywords: body composition; obesity; skin reflectance; sun exposure; vitamin D.

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Figures

FIGURE 1
FIGURE 1
Consort diagram adapted from (23).
FIGURE 2
FIGURE 2
Sun exposure diary (A) and clothing key (B) used in the current study.
FIGURE 3
FIGURE 3
Seasonal differences in average time outside (A), sun exposure index (SEI) (B), body surface area exposed (C), cumulative joules over the 12-wk study period (D), cumulative joules/number of days with recorded exposure (E), and weekday and weekend scaled sun exposure (sum of the cumulative weekday and weekend joules adjusted for number of recorded days) (F). Fall (n = 8), winter (n = 15), spring (n = 17), summer (n = 23). Groups without a common letter differ by Dunn's test (P < 0.05).
FIGURE 4
FIGURE 4
Seasonal differences in postintervention serum 25-hydroxyvitamin D [25(OH)D] concentrations (A), skin reflectance measurements (B), and dietary vitamin D intakes (C). Fall (n = 8), winter (n = 15), spring (n = 17), summer (n = 23). Groups without a common letter differ by Dunn's test (P < 0.05).
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