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Vitamin D2 or D3?

Friday, February 23, 2018

Mid-February is a time when many folks who do not enjoy cold weather outdoor sports will want to consider vitamin D supplementation. Today's Friday Pearl speaks to the two different types of vitamin D available in supplement form.

A case can be made against synthetic Vitamin D2 (ergocalciferol) as a vitamin supplement, although pharmacopoeias still regard D2 and vitamin D3 (cholecalciferol) as equivalent and interchangeable.

An article published in the American Journal of Clinical Nutrition revealed that the presumption of equivalence was based on studies of rickets prevention in infants conducted more than 70 years ago.

Fortunately, nutrition science and medicine move forward and the emergence of the 25-hydroxyvitamin D lab test, as a measure of vitamin D status, provided an objective, quantitative measure of the biological response to vitamin D administration. Vitamin D3 has proven to be the far more potent form of vitamin D in all primate species, including humans.

It was initially thought that both vitamin D2 and D3 follow the same metabolic pathway. However, minor differences in the chemistry of side chains between the two forms of vitamin D result in differences in the site of hydroxylation and lead to the production of unique biologically active metabolites.

Unfortunately, the form of synthetic vitamin D used in prescription formulations in our country is still vitamin D2, which is not the form produced in the human body by the sun or the form found in fish. Fish store quantities of vitamin D3 in their liver and fat tissue, but they do not synthesize vitamin D and are fully dependent on dietary sources. They are also dependent on the same dietary sources to produce omega-3 fatty acids, EPA and DHA,  Once again, fish act as the middle man.

Based on differences in efficacy at raising serum-25 hydroxyvitamin D levels, diminished binding of vitamin D2 metabolites to vitamin D-binding protein linked to its shorter shelf and half life, we suggest it is not the most suitable for supplementation or fortification.

Both pharmaceutical and supplemental vitamin D2 are fungus / yeast derived. Vitamin D2 was discovered in the 1920s through ultraviolet light exposure of plants. The process was patented and licensed to pharmaceutical companies, which led to a prescription preparation of vitamin D2 called viosterol.

Supplemental vitamin D3 is derived from two places: cod liver oil or sheep skin lanolin exposed to ultraviolet light, which makes it an animal product. Unfortunately, natural (18:12) TG fish oil, concentrated EE and TG fish oil, and krill oil supplements do not include enough vitamin D3 to make a supplement label claim.

If a vitamin D3 label-claim is made, it is most likely from sheep skin lanolin, unless the label is also making a vitamin A claim, because including enough cod liver oil to make a vitamin D3 claim will include enough vitamin A to require label identification.

Vegetarians and vegans will usually be vitamin D deficient unless they get a lot of sun, particularly if they are over age 50. Supplementation with D3 or consumption of foods fortified with vitamin D2 is a must for these people.

Ellen Troyer, with Spencer Thornton, MD, David Amess and the Biosyntrx staff


While we agree with most vitamin D researchers who suggest the current Vitamin D recommendations are way too low, given the enormous amount of new Vitamin D science, and to reach the vitamin D sufficiency goal of 30 to 50 (OH) D ng/ml (nanograms per milliliter), we also warn against super megadosing vitamin D, which can lead to toxicity and a buildup of calcium in blood (hypercalcemia).                                                                                    

The National Institutes of Health Office of Dietary Supplements daily vitamin D recommendations are 600 IU for those between the ages of one year and 70, and 800 IU for those over 70. Their safe upper limit (UL) is 4,000 IU per day.

Before dramatically increasing your vitamin D intake, discuss the increase with a nutrition savvy doctor and remember to consider the amount in your daily multiple and other supplements you might be taking, as well as the amount you are consuming in fortified foods.

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