title: The effect of vitamin D supplementation on serum 25(OH)D in thin and obese women.
abstract: Obese people are known to have lower serum 25OHD levels compared to non-obese people. It is not known whether it is due to storage of vitamin D in fat, inadequate input from sunlight, diet or other unknown factors. We examined the relationship at study baseline of serum 25OHD, PTH, 1,25(OH)2D with body composition measurements using dual energy X-ray absorptiometry. The results showed a significant inverse relation between total body fat mass and serum 25OHD (p<0.0001) and serum 1,25(OH2)D (p=034) and an independent positive correlation between serum PTH and total body fat mass (p<0.0001). In a randomized controlled study of seven doses of vitamin D (400-4800IU/d) the increase in serum 25OHD levels was compared in women with a normal body mass index to obese women. The response to the low doses of vitamin D (400-800IU/d) was significantly less than that of the medium (1600-2400IU/d) and high doses groups (3200-4800IU) (p<0.0001) in all BMI categories. The increase in serum 25OHD in the medium and high dose groups was not significantly different with increasing level of obesity. But thinner women with a normal BMI (<25kg/m(2)) showed a much higher response to vitamin D at any dose level compared to other BMI groups. There was no significant change in total body fat mass after treatment with vitamin D or calcitriol in our randomized trials. In summary, the response to vitamin D is dependent on body weight. Women with BMI <25kg/m(2) develop much higher levels of serum 25OHD after vitamin D supplementation compared to those with BMI of >25kg/m(2). The differences in serum 25OHD levels between normal and obese women may be due to differences in volume dilution. After vitamin D supplementation, all obese women reach adequate levels of serum 25OHD but normal women (BMI<25kg/m(2)) reach much higher levels of 25OHD and in this group smaller doses of vitamin D used should be used. This article is part of a Special Issue entitled 'Vitamin D Workshop'.
authors.affiliation: Bone Metabolism Unit, Creighton University Medical Center, Omaha, NE, United States. jcg@creighton.edu
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Gallagher
authors.forename: Vinod
authors.initials: V
authors.lastname: Yalamanchili
authors.forename: Lynette M
authors.initials: LM
authors.lastname: Smith
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000187:drug effects / Q000502:physiology; D015992:Body Mass Index; D002117:Calcitriol / Q000008:administration & dosage; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000178:diet therapy* / Q000473:pathology; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002117:Calcitriol