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Vitamin D: Pros and Cons

Can increasing vitamin D intake above the current recommended dietary allowance really cure or prevent other health conditions?
Vitamin D - Pros and Cons
By Jane Langille
Published: May 29, 2014
Last updated: June 15, 2016

In the last several years, there has been a flood of health news about studies linking vitamin D deficiency with cancer, cardiovascular diseases, diabetes, metabolic disorders, depression, infectious diseases, autoimmune diseases, mortality and even autism. A search on PubMed for vitamin D finds more than 1,400 papers listed from January to April 2014 alone.

As a result of this increased interest, some people are boosting their intake above the recommended dietary allowance hoping that extra vitamin D might help prevent, treat or cure a host of adverse disease conditions.

Vitamin D supplementation is proven to be effective to help maintain good bone health, but can increasing intake above the current recommended dietary allowance really cure or prevent other health conditions?

Vitamin D and Arthritis

Dawn Hunter, a freelance editor based in Toronto, Ontario, takes 2,000 IU (international units) of vitamin D daily, even though some health guidelines call for a much smaller dose of 600 IU per day. “Every time I stop taking it, my levels just plummet,” says Hunter, who has arthritis and says that she does not have the opportunity to get much natural sunshine.

Five years ago, Hunter found out she was severely deficient after her rheumatologist ordered a blood test. She addressed her deficiency by taking 4,000 IU daily for a year to boost her blood level from 14.8 ng/mL (nanograms per milliliter) and has been maintaining her level at 30.4 ng/mL with a daily dose of 2,000 IU for the past 4 years. (The normal range is 30.0 to 74.0 ng/mL).

“When my vitamin D level increased, I noticed a small reduction in the general ache I had with my arthritis,” notes Hunter. “My rheumatologist says there is some evidence that arthritis can progress faster in people who have low levels of vitamin D. I was just turning 40 when my arthritis was diagnosed, so managing progression is important to me.”

Vitamin D is really a hormone

Vitamin D is actually a pro-hormone that is involved in many metabolic processes. Your body makes vitamin D from sunlight on your skin,. You can also take supplements and you can get a small amount from fortified food sources such as milk or orange juice.

Supplements come in two formats: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is found naturally in sun-exposed mushrooms. Vitamin D3 is the form made naturally in human skin and is made from a cholesterol precursor obtained from lanolin. It can be found in oil-rich fish like salmon, mackerel and herring. There is some evidence that the D3 format is more bioavailable. Vitamin D is fat-soluble, meaning that if you take too much, the excess is not excreted in urine.

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In your body, your liver converts vitamin D from sunlight or supplements to 25-hydroxyvitamin D, [25(OH)D], the form that is measured in a blood test. The 25 (OH)D is then converted again, mostly in the kidneys, to the activated form of vitamin D, a hormone called calcitriol (1,25-dihydroxyvitamin D).

It’s plausible that vitamin D may play a role in a host of other diseases and conditions such as cancer, cardiovascular disease and diabetes, because there are calcitriol receptors on nearly all tissues in the body. Calcitriol plays a role in regulation of over 900 different genes. In cell culture and animal studies, researchers have found that calcitriol is involved in cell differentiation, proliferation and inhibition, inflammation, and the synthesis and secretion of insulin. Calcitriol also has an impact on brain function and development. Two U.S. researchers recently proposed a mechanism to explain how calcitriol may be involved in the regulation of the production of serotonin, a brain chemical that is often out of balance in autistic children.

At first blush, it may seem hard to believe that vitamin D could be associated with so many different conditions. However, John J. Cannell, MD, Founder and Executive Director of the Vitamin D Council, says, “Many people are turned off by these claims and say it’s impossible that one thing is involved in so many different disease processes, but they are unaware of the mechanism of vitamin D. It is actually a steroid hormone precursor that turns genes on and off. There are at least a thousand genes that are directly regulated by vitamin D.”

Next: Studies on vitamin D >>

Jane Langille

Jane Langille

Jane Langille is a health and medical writer based near Toronto, Ontario. Jane writes about health news and medical innovations for media publications and health care providers

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