Cholecalciferol benefit, side effects, safety, source, versus ergocalciferol
Long term safety and risks, benefit for cancer and heart disease, what is the right dosage, 400 iu, 1000, 2000, 3000, 5000, or 10,000 units
April 5 2016 by Ray Sahelian, M.D.

Vitamin D3 or cholecalciferol is produced in skin and is sequentially metabolized by the liver and kidney to the biologically active form 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. It is a seco-steroid hormone that regulates calcium homeostasis within the body.

Types of vitamin D available to purchase
Supplemental vitamin D is available in 2 distinct forms: ergocalciferol ( vitamin D2 ) and cholecalciferol ( vitamin D3 ). The latter has proven to be the more potent form in all primate species, including humans. Vitamin D3 can also be produced in the skin through exposure to sun. Subsequently, it is metabolized by the liver and kidney to the biologically active form 1,25-dihydroxyvitamin D3.

Buy Cholecalciferol, Vitamin D3, 400 IU and 1000 units per pill
Dietary Supplement
Helps Maintain Normal Bone and Tooth Formation

Cholecalciferol helps the body to regulate the transport of calcium from the digestive system through the bloodstream to bone. It also assists in the retention of calcium and phosphorus. Nature's Way Vitamin D is 100% natural cholecalciferol.  The dry form is specially formulated for easy absorption.  It contains no artificial ingredients or preservatives.

Cancer, tumor prevention
Epidemiological studies and work on experimental animals strongly suggest a protective effect of cholecalciferol vitamin D3 (1,25(OH)2D3) against colon cancer and several other cancers. The correlation between decreased morbidity and mortality of cancer and exposure to sunlight is known. The many biological functions of vitamin D that contribute to cancer prevention have only recently begun to be appreciated. Once activated 1,25-dihydroxyvitamin D [1,25(OH)2D3] functions as a potent inhibitor of normal and cancer cellular proliferation.

Bone fracture
The effect of cholecalciferol (vitamin D3) on the risk of fall and fracture: a meta-analysis.
QJM. 2007. From the Evidence Research Unit, Macclesfield, UK, Merck & Co. Inc., Whitehouse Station, New Jersey, USA, and Nottingham City Hospital, Nottingham, UK.
We evaluated the effect of supplementation with cholecalciferol (excluding the potential effect of calcium supplementation) on the risk of fall and fracture, primarily in postmenopausal women, using a systematic literature review of MEDLINE, EMBASE, BIOSIS and the Cochrane Database of Systematic Reviews. There is a trend towards a reduction in the risk of fall among patients treated with cholecalciferol  alone compared with placebo, suggesting that cholecalciferol should be an integral part of effective osteoporosis management.

Cholecalciferol or ergocalciferol supplement?
The case against ergocalciferol (vitamin D2) as a vitamin supplement.
Am J Clin Nutr. 2006. School of Nutrition and Dietetics, Acadia University, Wolfville, Canada.
Pharmacopoeias have officially regarded these 2 forms as equivalent and interchangeable, yet this presumption of equivalence is based on studies of rickets prevention in infants conducted 70 y ago. The emergence of 25-hydroxyvitamin D as a measure of vitamin D status provides an objective, quantitative measure of the biological response to administration. As a result, cholecalciferol has proven to be the more potent form of vitamin D in all primate species, including humans.

Source
I am a vegetarian from India and do not use animal products (except milk) which are made by sacrificing / killing of animals. Presently I am working as postdoctoral research scientist in University of Copenhagen, Denmark. Since the winters are starting soon and I do not get sufficient exposure to sunlight so I developed deficiency of Vitamin D. My doctor advised me to take supplements because there is no direct sunlight in Copenhagen during winters. Eating animal products hurts my religious beliefs, thus I want to know about the actual production source (whether from animals, vegetables, synthetic or semisynthetic) of the Vitamin D in the tablets which you provide.
   Cholecalciferol has an origin from animal products such as sheep wool. The sheep are not killed. The wool is sheared, and lanolin from the sheep wool is chemically altered in the lab to produce vitamin D3 or cholecalciferol.

I would like your thoughts on whether taking vitamin D3 cholecalciferol is okay for someone who is allergic to wool.
   I have not heard of any problems arising from ingestion in someone who is allergic to wool, but I cannot be 100 percent that it is completely safe since I am not familiar with the details of the manufacturing process of cholecalciferol from sheep wool.

Questions
I read on a web site that "Vegans usually obtain vitamin D from the action of sunlight on the skin or by taking fortified foods such as soya milk, margarine, breakfast cereals and vitamin supplements which are made from yeast or other fungi. Fortified vegan products contain D2 ( ergocalciferol ). Vegans are careful about their source of Vitamin D as D3 ( Cholecalciferol ) which is animal-derived." I'm vegan, does this mean I should not take a product with cholecalciferol but rather take ergocalciferol?
   It appears to be true that Vitamin D in the form of cholecalciferol is derived from an animal source such as sheep wool. Therefore, this would make it fine for a vegetarian but not for a very strict vegan who believes that even a vitamin derived from wool is not acceptable. The sheep are not killed. The wool is sheared, and lanolin from the sheep wool is chemically altered in the lab to produce vitamin D3 or cholecalciferol.
 
I have seen research stating that vitamin D2 should not be used, only vitamin D3 cholecalciferol, as a milk additive and for personal health reasons.
    The preliminary research states that cholecalciferol is preferable to ergocalciferol. However, we have not seen any long term human studies in a head to head comparison of the two forms to know for certain, but for the time being the former is probably the better choice.

I live in Boston, USA. I read your article about “Cholecalciferol benefit versus ergocalciferol. I take 4000 IU of Vitamin D3 daily. I do not know if this is from wheel wool or not. Can you please tell me a brand that is derived from sheep wool. In USA Nature's Bounty, Nature Made, Spring Valley are the popular ones.