Vitamin D and its metabolites appear to have several functions in adipose tissue. Vitamin D is significantly stored and may then be slowly released from the adipose tissue when serum vitamin D levels decrease 10 , or it may be hydroxylated within adipose tissue to 25 OH D and 1,25 OH 2 D 4.
Because the serum vitamin D half-life is known to be 15 to 24 hours 19 , long-term effects after high doses of oral vitamin D or UVB light would be impossible without storage either as vitamin D or as 25 OH D. However, the amount of 25 OH D found in adipose tissue was fairly small. In our study, the calculated half-life of serum 25 OH D in the preterminal phase 0 to 3 months was This is almost identical to the half-life of 82 days found by Oliveri et al. In their study, subjects were followed up for 2 months after a bolus of , IU of vitamin D with supplementation of IU of vitamin D per day from day 7 to day 20, and the half-life was calculated on the basis of the area under the curve 9.
Similarly, in a study by Cipriani et al. Meanwhile, the terminal half-life of serum 25 OH D months 3 to 12 in our vitamin D group was days, indicating a much slower decrease of serum 25 OH D after the first 3 months. Our approach to calculate half-life using 25 OH D levels after subtraction of the levels in the placebo group minimized confounding due to ongoing low-dose vitamin D supplementation.
This also enabled us to evaluate the half-life of circulating 25 OH D accumulated as a result of high-dose vitamin D supplementation. If serum half-life were calculated using per se levels of 25 OH D, the preterminal and terminal half-lives would have been even longer. Because the traced half-life of serum 25 OH D is only about 15 to 25 days 7 , 8 , the gradual release of vitamin D stored in adipose and other tissues can at least partly explain the slowly declining serum 25 OH D levels 4. However, it should be stressed that in comparison with other studies on storage of vitamin D in adipose tissue Supplemental Table 1 , our randomized, controlled trial was very long, which might have caused saturation of vitamin D deposition at some time.
Furthermore, only Heaney et al. Thus, Heaney et al. After 3 months of supplementation with 50, IU of vitamin D weekly, the mean fat vitamin D level in the study by Heaney et al. Meanwhile, the mean serum 25 OH D level at the end of the intervention in the study by Heaney et al.
Thus, the fairly similar accumulation of vitamin D in the short-term study by Heaney et al. It should be noted that the circulating levels of 25 OH D in the vitamin D group declined fairly rapidly. Accordingly, the release of vitamin D from adipose and other tissues in our study was limited even after long-term high-dose vitamin D supplementation.
In another study, Heaney et al. Given no vitamin D from the diet and no UVB exposure, the adipose tissue vitamin D stores after 3 months of supplementation with 50, IU per week would be rapidly depleted within approximately 50 days , and the authors concluded that vitamin D stored in adipose tissue was of relatively minor importance 1.
In contrast, our study, in which serum 25 OH D levels were actually followed up over time after supplementation was stopped, showed prolonged benefit of stored vitamin D, which may indicate that significant storage also occurred in other tissues than fat. However, it is worth mentioning that the calculations of adipose tissue are very rough; as in other studies in which vitamin D in adipose tissues has been reported, the levels appeared to vary not only with intake of vitamin D and type of subjects included but also with which fat compartment the biopsy was taken from Supplemental Table 1 23 — Thus, in an autopsy study by Lawson et al.
Nevertheless, as in our study, the number of subjects included in all these studies was small, and larger sample sizes are needed to draw firm conclusions. Our study also had several other limitations. Although the intake of vitamin D supplements and sun exposure were registered and used as covariates, the diet was not standardized, nor was the intake of vitamin D from the diet calculated.
We did not measure serum vitamin D levels, which could have given additional valuable information. We took biopsies only from subcutaneous adipose tissue, and we had no information on vitamin D storage in other tissues. The prevalence of vitamin D supplementation in the study group was high and could have interfered with the serum 25 OH D levels.
Our study does not provide information on whether the storage and release of vitamin D in adipose tissue is an active or passive process; because we have biopsies from only one vitamin D group, we cannot reach conclusions about dose-response relationships.
Our study also has some strengths. It was double-blind and prospective; external factors such as sun exposure and BMI were comparable in the two groups. In addition, for serum 25 OH D levels during the follow-up period, we had sufficient power to detect a significant difference between the two groups even after 12 months.
In conclusion, our study strongly indicates that vitamin D stored in adipose and possibly other tissues is physiologically important and may partly explain why serum 25 OH D levels do not fall to critically low levels during the winter. However, this has to be tested experimentally with a design that is more similar to, or better mimics, ordinary summer and winter periods than our study design.
The funding institutions had no role in the study design, data analysis and interpretation, decision to publish, or preparation of the manuscript. Clinical Trial Information : ClinicalTrials. NCT registered 13 November Disclosure Summary: The authors have nothing to disclose. Vitamin D 3 is more potent than vitamin D 2 in humans. J Clin Endocrinol Metab.
Google Scholar. The distribution and storage of vitamin D and its metabolites in human tissues. Clin Sci. DeLuca HF. Overview of general physiologic features and functions of vitamin D.
Am J Clin Nutr. Abbas MA. Physiological functions of Vitamin D in adipose tissue. Here are eight symptoms that may indicate you have a vitamin D deficiency, as well as causes, treatments, and more. Vitamin D is essential for health, but it can be hard to get enough of it from your diet. Here are 7 healthy foods that are high in vitamin D. Regular sun exposure is the most natural way to get enough vitamin D, but too much sunlight comes with health risks.
This article explains how to…. The amount of vitamin D you need depends on several factors. This article explains exactly how much vitamin D you should be taking. Vitamin D is an important nutrient that may also have benefits for weight loss. This article explores the relationship between vitamin D and body…. Vitamin D is very important for your health, but it is possible to get too much of it. This article explores 6 side effects of taking too much vitamin…. It appears vitamin D can help prevent gum disease, an ailment that can increase the risk of diabetes.
Higher levels can increase your efficiency in using oxygen. That can improve your exercise regimen. Health Conditions Discover Plan Connect. What Is Vitamin D? Best Food Sources. Symptoms of Deficiency. Potential Health Benefits. How Much Should You Take? Optimize Your Other Nutrients. The Bottom Line. Read this next. The Benefits of Vitamin D. Breast milk doesn't have much vitamin D in it. That's what spurred a recommendation from the American Academy of Pediatrics that every breastfed infant be given vitamin D if they're being given liquid multivitamin drops, they're getting enough of it.
There are claims that one needs to get a certain amount of sun exposure every day in order to produce enough vitamin D to be healthy. The majority of people can get their vitamin D from nutritional supplements and from vitamin D-fortified foods. There are some people who are typically not dermatologists or experts in the biology of skin cancer who have advocated for tanning to get vitamin D.
But we know that UVB light causes skin cancer and that protecting yourself against it makes sense. As a doctor who treats patients who have melanomas, I want the general public to be advised that under no circumstances can use of a tanning bed or tanning in general be justified on the basis of vitamin D. Take a supplement instead. Click here for more information about Yale Medicine's Endocrinology Department. Or to make an appointment call Skip to Main Content.
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