Modern medicine has long considered that vitamin D3, cholecalciferol, and vitamin D2, ergocalciferol, to be equal.  That is these two compounds will give you exactly the same clinical response.  This has been a huge mistake.  This extreme error in medicine has cost tens of millions of lives and an unbelievable amount of suffering.  It is true that in small amounts, vitamin D2 will cure rickets. In larger amounts it becomes extremely toxic at much-much lower levels than vitamin D3.  When the IOM’s Food and Nutrition Board set standards for vitamin D, they address this issue by saying that a serum level for 25(OH)D of twenty nanograms per milliliter made from vitamin D2 was adequate for bone health. They then warned that levels above fifty nanograms per milliliter could result in health issues.  This is absolutely correct when using vitamin D2 or the stuff that your doctor typically prescribes.  Until recently, vitamin D3 was not available for prescriptions.  Under US law, if a doctor prescribes a vitamin to prevent, cure, or treat a disease, it becomes a drug.  The medical profession has been extremely concerned of this issue of toxicity from either vitamin D2 or toxisterols that occur from over irradiation when making D2.

It gets even more complicated because vitamin D3 is not a vitamin but a prohormone.  It is the substance that our body produces when we are exposed to the UV rays from the sun or our natural connection to the sun that was forever altered with the introduction of sunscreen products.  Consider the importance of hormones.  Would you give a person estrogen if they had a testosterone deficiency?  They are very similar in molecular weight and only differ by the placement of oxygen and OH groups.  They are hormones and typically affect the expression of over one hundred fifty genes.  The mix up of these two hormones would cause a significant failure of biological functioning.  Vitamin D3 affects the expression of over two hundred genes and over twenty seven hundred genes have been found to have vitamin D pathways.  So would you want to mix up D2 with D3 that could cause your health to fail?

If you are totally deficient in vitamin D, then a small amount of D2 may be acceptable medical practice until you can get an adequate amount of D3 from either supplementation or spending time in the sun.  To show you how the medical schools have taught physicians, my doctor told me that if I took five thousand IU’s per day of vitamin D that my organs would turn to stone.  Of course this was before I encouraged him to read the research.  The calcification of organs and soft tissue has long been an issue with vitamin D2 and rightly so.  However, this has lead to a huge problem with vitamin D3 deficiency where the importance of this vitamin or if you prefer hormone, is not just about bone health.  To think that our venerated institutions that we depend on to give us scientific direction for health stated that they only considered bone health when reviewing vitamin D is outrageous.  One of the most important hormones in our body and our health institutions give it a ‘one note’ function.  It is time that the medical profession gets on with orchestrating the symphony.

I recently had a friend tell me his doctor had just prescribed D2 because his 25(OH)D was 15 ng/ml.  I tried to explain the difference between D2 and D3 but it seemed to fall on deaf ears.  He kept asking the medical difference and he did not seem to believe the answer.  Do not allow yourself to fall into this trap.  If your doctor tells you to take fifty thousand IUs of vitamin D2 per week, ask if you can use the natural substance your body makes, vitamin D3.  If he says no, then find a new doctor because the one you have does not know what he is doing.   – Pandemic Survivor

For the best explanation, The Vitamin D Problem, by Moon and Reich from 1975 that includes the history.  A PDF file.