Vitamin D

Vitamin D is unusual, because in some ways it acts as a nutrient, and in some ways it acts as a hormone. Vitamin D can be made from cholesterol in the body by skin exposure to sunlight. However, many people do not receive enough skin-sunlight exposure to make adequate Vitamin D.

The active form of vitamin D is 1,25-dihydroxy-vitamin-D3 (calcitriol), which is made in the kidneys from the precursor 25-hydroxy-vitamin-D3.

According to [Marz1999, pg 175], "it is estimated that the RDI [recommended daily intake] can be achieved with the exposure of 30% of a person's skin surface for 30 minutes at moderate latitudes." [Marz1999, pg 177] notes that "the darker the skin the less vitamin D will be produced, with as much as 95% blockage of UV light in people with very dark skin."

Dr. Weyrich notes that many people are concerned about the possibility of excess sun-exposure causing skin cancer; he also notes that if the percentage of a person's exposed skin surface is doubled, the required exposure time can be halved in order to obtain the same level of Vitamin D production.

Vitamin D plays an important role in [Gaby2011, pg 108]:

• Calcium and phosphorus absorption and regulation.
• Immune regulation.
• Bone health.
• Neuromuscular function.
• Cellular growth and differentiation.
• Regulating insulin secretion and action.

Symptoms of Vitamin D deficiency include:

• Rickets, osteomalacia, osteoporiosis
• Poor sleep, insomnia
• Poor immune function
• Fibromyalgia, chronic fatigue syndrome, depression [Gaby2011, pg 109].

Symptoms of excess Vitamin D consumption include [Gaby2011, pg 122]:

• hypercalcemia, hypercalciuria
• fatigue, anorexia, nausea, vomiting
• polyuria, polydipsia
• cardiac arrhythmias
• calcification of the kidneys which may progress to renal failure

There are several different forms of "Vitamin D" [Marz1999, pg 175]:

• Vitamin D3: cholecalciferol - made by sunlight exposure of the skin (also found in various animal products such as cod-liver oil).
• 25-hydroxycholecalciferol - Made by the liver from cholecalciferol.
• 1,25-dihydroxycholecalciferol - Made by the kidneys from 25-hydroxycholecalciferol. Also available as the drug "Calcitriol". Most active form.
• Vitamin D2: ergocalciferol - Made by plants (vegan, but not as bio-available). Often used as a supplement in dairy products; available in prescription form. Special testing is required to evaluate Vitamin D2 status.

Dr. Weyrich notes that while Vitamin D clearly exerts hormone-like activity in the body, it does not seem to be regulated by a typical negative feedback loop. Dr. Weyrich surmises that the hormonal control may be at the 25-hydroxycholecalciferol or 1,25-dihydroxycholecalciferol level, rather than at the cholecalciferol level (i.e. cholecalciferol is a pro-hormone, not a hormone). [Marz1999, pg 176] not'24' rather than the '1' position in response to calcitonin, which is secreted in response to high serum calcium. Increased blood calcium (results in decreased PTH and an increased calcitonin which deposits Ca⁺⁺ into bone). The Chinese have always linked bone health with the kidneys. It seems that the kidneys play a key role in the final hydroxylation step. It may be that decreased perfusion to the kidneys due to atherosclerosis, or a combination of boron, magnesium or estrogen deficiency may also be involved." Further study is required.

Some people are genetically predisposed to produce more Vitamin D from sun exposure than others.

Standard blood tests for vitamin D3 may be misleading in cases of kidney disease or genetic variants that reduce the conversion of cholecalciferol to 1,25-dihydroxycholecalciferol. See also the discussion found at [Gaby2011, pg 113].

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  Vitamin K

•       [Gaby2011]   Alan R. Gaby. Nutritional Medicine. Concord, NH: Fritz Perlberg Publishing (2011). Amazon
•       [Marz1999]   Russell B Marz. Medical Nutrition from Marz, Second Edition. Portland, OR: Omni-Press (1999). Amazon