Decreased bioavailability of vitamin D in obesity.
BACKGROUND
Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism.


OBJECTIVE
This study assessed whether obesity alters the cutaneous production of vitamin D(3) (cholecalciferol) or the intestinal absorption of vitamin D(2) (ergocalciferol).


METHODS
Healthy, white, obese [body mass index (BMI; in kg/m(2)) > or = 30] and matched lean control subjects (BMI </= 25) received either whole-body ultraviolet radiation or a pharmacologic dose of vitamin D(2) orally.


RESULTS
Obese subjects had significantly lower basal 25-hydroxyvitamin D concentrations and higher parathyroid hormone concentrations than did age-matched control subjects. Evaluation of blood vitamin D(3) concentrations 24 h after whole-body irradiation showed that the incremental increase in vitamin D(3) was 57% lower in obese than in nonobese subjects. The content of the vitamin D(3) precursor 7-dehydrocholesterol in the skin of obese and nonobese subjects did not differ significantly between groups nor did its conversion to previtamin D(3) after irradiation in vitro. The obese and nonobese subjects received an oral dose of 50000 IU (1.25 mg) vitamin D(2). BMI was inversely correlated with serum vitamin D(3) concentrations after irradiation (r = -0.55, P: = 0.003) and with peak serum vitamin D(2) concentrations after vitamin D(2) intake (r = -0.56, P: = 0.007).


CONCLUSIONS
Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments.
Wortsman
J
J
Southern Illinois University School of Medicine, Springfield, USA.
Matsuoka
L Y
LY
Chen
T C
TC
Lu
Z
Z
Holick
M F
MF
D000328:Adult; D001682:Biological Availability; D015992:Body Mass Index; D002762:Cholecalciferol / Q000097:blood / Q000378:metabolism; D004872:Ergocalciferols / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology; D006801:Humans; D007408:Intestinal Absorption; D009765:Obesity / Q000097:blood / Q000378:metabolism* / Q000473:pathology; D012016:Reference Values; D012867:Skin / Q000378:metabolism; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000493:pharmacokinetics*
D004872:Ergocalciferols; D014807:Vitamin D; D002762:Cholecalciferol