Abstract
Cholecalciferol is known to be deposited in human adipose tissue, but it is not known whether 25-hydroxyvitamin D (25(OH)D) is found in detectable concentrations. Therefore, our objective was to determine whether 25(OH)D is detectable in subcutaneous white adipose tissue (SWAT) in overweight and obese persons enrolled in a twelve week energy restricted diet. Baseline and post-intervention gluteal SWAT biopsies were collected from 20 subjects participating in a larger clinical weight loss intervention. LC-MS/MS was utilized to determine SWAT 25(OH)D concentrations. Serum 25(OH)D and 1,25(OH)2D were measured by RIA. Body composition was assessed by dual energy x-ray absorptiometry. SWAT 25(OH)D concentrations were 5.8 ± 2.6 nmol/kg tissue and 6.2 ± 2.7 nmol/kg tissue pre- and post-intervention SWAT, respectively. There was a significant positive association between SWAT 25(OH)D concentration and serum 25(OH)D concentration (r = 0.52, P < 0.01). Both SWAT and serum 25(OH)D concentrations did not significantly change after a twelve-week period of energy restriction with approximately 5 kg of fat loss. In conclusion, we have demonstrated our LC-MS/MS method can detect 25(OH)D3 in human subcutaneous fat tissue from overweight and obese individuals and is consistent with previously reported concentrations in swine. Additionally, our findings of no significant changes in SWAT 25(OH)D3 or serum 25(OH)D after a 6% loss of total body weight and 13% reduction in total fat provides the first human evidence that adipose 25(OH)D does not likely contribute to serum 25(OH)D with moderate weight loss; whether this is also the case with larger amounts of weight loss is unknown. Weight loss alone is not sufficient to increase serum 25(OH)D and increases in dietary or dermal biosynthesis of vitamin D appear to be the most critical contributors to in vitamin D status.
Highlights
The analysis of vitamin D metabolites in adipose tissue is rare and likely due to difficulties in extracting and separating the metabolites from tissue matrices [1]
Dietary vitamin D intakes were below current recommendations of 600 IU/day; the study was conducted during the previous recommendations of 200 IU/day
We have demonstrated a LC-MS/MS method that can detect 25(OH)D in human adipose tissue collected from overweight and obese individuals enrolled in a clinical weight loss intervention
Summary
The analysis of vitamin D metabolites in adipose tissue is rare and likely due to difficulties in extracting and separating the metabolites from tissue matrices [1]. There is a disparity in the literature between analyses of the parent compound, cholecalciferol, and the other vitamin D metabolites in adipose tissue. This would be expected since it has been well-established that cholecalciferol is the dominant metabolite distributed in adipose tissue [2]. There are only two reports of measurable concentrations of 25(OH)D in adipose tissue from human cadavers [2] and in swine [3]; suggesting a small yet quantifiable site of 25(OH)D deposition in adipose tissue. The data used for this estimation were from swine adipose tissue [3]. There have been no reports of adipose 25(OH)D analyses in healthy human subjects
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