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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Effect of supplementation on vitamin D status: Thin and obese women

Many studies have shown an inverse relationship between 25OHD and obesity. Some possible explanations include the popular fat sink (increased storage in the adipose tissue), sedentary lifestyle of the obese, low sunlight exposure among the obese, genetic changes in obesity or other unknown factors. The concept of a fat sink is popular but no randomized controlled trial ever explored the issue. Animal studies show that the vitamin D is stored in muscle, liver and skin, as well as fat.

Professor Reinhold Vieth, long ago, first objected to the popular theory that fat serves as a sink, trapping vitamin D. From what Dr. Vieth could tell, such a complicated explanation was not needed. Fat people have lower vitamin D levels because what vitamin D they do have is diluted by body weight. There is no need for a complicated fat-soluble sink, which traps vitamin D; volume distribution explains it just fine.

J. Christopher Gallagher, MD, and colleagues of Creighton University Medical Center recently found that Vieth was right. They conducted a randomized controlled trial to discover that  differences in serum 25OHD levels after various doses of vitamin D among normal-weight and obese patients are simply due to volume dilution.

Gallagher JC, Yalamanchili V, Smith LM. The effect of vitamin D supplementation on serum 25OHD in thin and obese women. J Steroid Biochem Mol Biol. 2012 Dec 11

The authors examined dose response curves to vitamin D in 163 older women according to BMI and by dividing  the 163 women into seven vitamin D dose groups (400, 800, 1600, 2400, 3200, 4000 and 4800 IU/day). After a year, the higher doses increased 25(OH)D by about 35 ng/ml while the lower doses increased it by about 15 ng/ml. They confirmed their previous finding that at 25(OH)D levels around 45 ng/ml, the body begins to change how it metabolizes vitamin D; that is, the liver’s wide open metabolic funnel of vitamin D into 25(OH)D begins to be regulated.

The lower dose groups showed little variation in serum 25OHD changes across all BMI groups. In the medium and high dose vitamin D dose groups, only thin women with a normal BMI show higher changes in vitamin D levels. The authors concluded,

“The dose response curves are so parallel between thin and obese people that the difference in serum 25OHD levels must be due to a volume dilution effect.”

Further reading:

Body weight and vitamin D blood levels

  About: John Cannell, MD

Dr. John Cannell is founder of the Vitamin D Council. He has written many peer-reviewed papers on vitamin D and speaks frequently across the United States on the subject. Dr. Cannell holds an M.D. and has served the medical field as a general practitioner, emergency physician, and psychiatrist.

One Response to Effect of supplementation on vitamin D status: Thin and obese women

  1. Rita and Misty says:

    I’m wondering if the rate of increase would slow down once a sufficient 25(0H)D level is reached in one’s body….

    Using myself as an example: my 25(OH)D levels as of 1.1.13 is 104 ng/ml. This is after supplementing with 32,000 iu of D3 daily since 10.1.12…..During the summer, my level was around 75 ng/ml with 16,000 iu D3 daily, and approx 2.5 hours of high sun per week (Connecticut’s version of sun)

    I’ve since cut back to 24,000 i.u. D3 daily…

    Since my body is completely sufficient now regarding Vitamin D, I am thinking that even with a high does of 24,000 i.u. D3 daily, the rate of increase will slow down….