Dr. Henry Cheng
Vitamin D is actually a group of fat soluble prohormones and not a true vitamin. The two major forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is the form produced in the skin after exposure to UVB radiation in sunlight and hence the most “natural” form of vitamin D. Vitamin D3 is also many folds more potent. It has been proven that lack of vitamin D leads to increase incidence of fractures. Vitamin D facilitates absorption of calcium in the intestine, prevents bone resorption, promotes resorption of calcium in the kidneys, and promotes mineralization of the skeleton. Deficiency can lead to rickets in children, osteomalacia in adults, and osteoporosis.
While most people know the benefits of Vitamin D for bone health, very few people know that Vitamin D also plays an important role in the maintenance of almost every organ and system in the body. It also influences the immune system and effects immuno-suppression and anti-cancer activities. Low vitamin D levels have been associated with multiple sclerosis, cardiovascular diseases, diabetes, sarcoid, tuberculosis, psychiatric disorders and auto-immune diseases. It has also been shown that deficiencies in Vitamin D predisposes an individual to frequent cold and influenza.
In 2007, the Canadian Cancer Society suggested a daily dose of 1000 IU of vitamin D per day for Canadian adults during fall and winter, and year round for high risk individuals including the elderly, the dark skinned and people who stay indoors. The recommendation came from findings that vitamin D is linked to anti-proliferative, pro-differentiative, and immunomodulatory functions. Research also indicated that vitamin D increases activities of natural killer (NK) cells, phagocytes, macrophages, monocytes, T cell and B cells. Being a prohormone, vitamin D interacts with hundreds of body genes. Other findings include inhibition of tumour blood vessel formation and cancer cell adherence. For these reasons vitamin D supplementation is thought to reduce cancer risk.
There are only a few foods that are rich in vitamin D: fatty fish, fish liver oils, fortified dairy products, some cereals, eggs and mushrooms. Half a cup of mushrooms provides as much as 2700 IU of vitamin D and is a rich source of vitamin D for vegans. 15 minutes of sun exposure of a significant body surface area twice a week without sunscreen will provide adequate vitamin D. Supplementation is needed if dietary intake or sun exposure is inadequate.
The best form of vitamin D supplement is cholecalciferol (D3) because not only is it the natural form made in the skin but it is also more potent than other forms. Vitamin D supplements are well tolerated. Health Canada sets the upper limit of daily dose as 2000 IU. Supplementation for children is desirable because maximum bone mass is not attained until 25 years of age. This is important especially for those who play computer games all day and do not drink much milk. There are 400 IU soluble and chewable tablets on the market labeled for children from newborn to 8. Vitamin D is measured in terms of micrograms (mcg.), but when you buy the supplement, read the equivalent in International Units (IU). As Vitamin K3 has also been related to healthy bones, I recommend a liquid Vitamin D3 with Vitamin K3 when the main goal is for bones.
