Are you a tree? 5. March 2009 William Davis (6) I assume you answered no. Then why would you consider taking the plant form of vitamin D (ergocalciferol)? That's the prescription form of vitamin D, often dispensed as 50,000 unit tablets. There's nothing wrong with plants. Some of my favorite foods are plants, full of nutritional value. Then why shouldn't vitamin D2 from plants be every bit as good as the human form of vitamin D? I believe the issue boils down to taking hormones from non-human sources. (Remember: Vitamin D is a hormone, a very powerful one at that.) Plants can be wonderful sources of flavonoids, fibers, protein, fats, vitamins, minerals, and other healthy components. But hormones? There are other examples of non-human hormones being given to humans with undesirable or unpredictable effects:--Xenoestrogens, phytoestrogens, and non-human mammalian estrogens--While non-human estrogens may partially mimic human estrogens, they can also block estrogen effects, or exert altogether novel effects. Non-human mammalian estrogens like Premarin can exert very peculiar (side-)effects, despite their role as prescription estrogen supplementation in humans. --Progestins--The synthetic versions of human progesterone, like their non-human estrogen counterparts, exert weird effects that are a world apart from real progesterone. --Sterols--Similar in structure to human cholesterol (while not a hormone, a building block for hormones), sterols have been used to reduce intestinal cholesterol absorption. However, if sterols are absorbed into the blood, they can enormously accelerate growth of atherosclerotic plaque. --Anabolic steroids--These modifications of the testosterone molecule build muscle, but also cause liver cancer, kidney failure, violent behavior, suicide and homicidal behavior. That's not normal. Outside of a pharmacologic effect (e.g., prednisone in place of human cortisol), there is no reason to take a non-human hormone in place of a human hormone. For that same reason, there is NO reason to take plant vitamin D2 (prescription or over-the-counter) in place of human vitamin D3.If the non-human hormone is identical to the human form, then there is no difficulty. The best example of this are thyroid hormones from pigs. That's what Armour Thyroid is, a thyroid hormone replacement that works wonderfully well.You will notice that virtually all of the examples of non-human hormones substituted for human hormones share one common motivation: profit. Synthetic or modified versions are more readily patent-protectable, unlike their natural counterparts which are not. Vitamin D2 is an anemic facsimile of the real human hormone, vitamin D3 (cholecalciferol). Stay away from it.