title: Reduced sun exposure does not explain the inverse association of 25-hydroxyvitamin D with percent body fat in older adults.
abstract: BACKGROUND
  Greater adiposity is associated with lower blood levels of 25-hydroxyvitamin D [25(OH)D]. The extent to which this results from reduced sun exposure among heavier individuals is unknown.
  
  
  OBJECTIVE
  This analysis was conducted to determine whether sun exposure habits differ according to percent body fat (%FAT) in older adults and to what extent they explain the inverse association of adiposity with 25(OH)D in that population.
  
  
  METHODS
  We performed a cross-sectional analysis of baseline data from a randomized trial of calcium and vitamin D supplementation to prevent bone loss.
  
  
  METHODS
  The study was performed at the Metabolic Research Unit at the Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University.
  
  
  METHODS
  A total of 381 generally healthy male and female volunteers age 65 and older participated in the study. Exclusion criteria included vitamin D and calcium supplement use, and medical conditions and medications known to affect bone metabolism.
  
  
  METHODS
  There were no interventions. Measurements for this analysis were made before participants received trial supplements.
  
  
  METHODS
  Plasma 25(OH)D, an indicator of vitamin D status, was measured.
  
  
  RESULTS
  Sunscreen use, hours spent outside per week, and percent of skin exposed did not differ across quartiles of %FAT (P > 0.43). 25(OH)D decreased across %FAT quartiles (P < 0.05) and was about 20% lower in the highest compared with the lowest quartile of %FAT after adjustments for age, sex, season, and vitamin D intake. Further adjustment for sun exposure habits had little effect on estimates of 25(OH)D.
  
  
  CONCLUSIONS
  In older adults, sun exposure habits do not vary according to adiposity and do not appear to explain lower 25(OH)D concentrations with increasing adiposity.
authors.affiliation: Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, Massachusetts 02111, USA. susan.harris@tufts.edu
authors.forename: Susan S
authors.initials: SS
authors.lastname: Harris
authors.forename: Bess
authors.initials: B
authors.lastname: Dawson-Hughes
mesh_terms: D050154:Adiposity / Q000502:physiology*; D000368:Aged; D001823:Body Composition / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006184:Habits; D006801:Humans; D008297:Male; D012727:Sex Characteristics; D016082:Solar System; D013473:Sunscreening Agents; D014807:Vitamin D / Q000097:blood*
chemical_list: D013473:Sunscreening Agents; D014807:Vitamin D