The Ultimate Guide: Vitamin D

What is Vitamin D?

Vitamin D is a steroid hormone that comes from cholesterol.  Since, I was a young child I have heard that you must go outside to get your daily dose of vitamin D.  So does it come from the sun or does it come from cholesterol?

The answer is both-

Vitamin D is not naturally occurring in many foods, so our bodies came up with an ingenious plan to harness the sun for our own benefit.

Once our skin is exposed to ultraviolet B light we begin to synthesize the vitamin D that we can use.  If you are a sun worshipper and feel recharged by the sun, this may be why.

Key point- the biologically inactive version that starts the process only has a half life of 12-16 hours.  That means that our liver must make great use of what we provide before it’s gone. 

So as you guessed, the next stop in the pathway is the liver where it is converted to 25-hydroxy vitamin D, 25(OH)D.  This is the form that’s most often measured in blood work.  This form of vitamin D can survive much longer and has a half life of three weeks.

Next stop is the kidney where it is converted into it’s biologically active form of 1,25 dihydroxy vitamin D also known as calcitriol. 

Calcitriol is the form of vitamin D that can enter target cells and bind to vitamin D receptors.

Main Function of Vitamin D

The main function of vitamin D is to maintain the balance between calcium and phosphate levels in the blood.  These levels are responsible for bone health and connected to over 900 genes involved in many processes throughout the body.

Vitamin D is considered an essential vitamin and deficiencies can be associated with mood, memory, cardiovascular disorders, metabolic disorders, cancer, hypertension, infectious diseases, and autoimmune disorders.

When working together with calcium, vitamin D can also help to protect against osteoporosis.

Levels of Vitamin D

Deficient = <20ng/ml

Insufficient = 20-30 ng/ml

Excess = >100 ng/ml

Intoxication = >150 ng/ml

Where is Vitamin D?

Like I said previously, vitamin D can be synthesized by exposing the skin to ultraviolet B rays from the sun. Can you overdose on vitamin D from the sun? The answer is NO! Your body has many protective mechanisms and this is one.  Your skin will not allow you to absorb or convert more previtamin D3 than you need.

It’s also found in fish skin such as tuna and salmon and fish liver oils, cod liver oil anyone?  You may also find it in some animal sources such as beef liver, eggs, and cheese.

Back in the 1930’s the united states government went to work to combat vitamin deficiencies and the fortification program was born.  This helped to combat many childhood diseases that used to plague children in socio-economic disadvantaged areas. Rickets is one such disease that is clearly linked to vitamin D deficiency.

Immune Response

Vitamin D has a very profound effect on the immune response.  Scientists are currently researching it’s link to lupus, autoimmune thyroid disease, diabetic nephropathy, and rheumatoid arthritis.

Monocytes and macrophages are the first line of defense against outside invaders in the body.  They increase anti-microbial activity.   A deficiency in vitamin D has been linked to an impaired ability of macrophages to mature, decreases production of macrophage specific surface antigens, decreased lysosomal enzyme acid phosphatase and decreased secretion of hydrogen peroxide.

It helps to decrease inflammation, which is a good thing. 

Overall, vitamin D plays an important role in the immune system and science is beginning to understand just how important that role is to our health.

Considerations

You should talk to your doctor about vitamin D supplementation before beginning any program.  Also, if you are taking corticosteroids as these can reduce calcium absorption and inhibit the metabolism of vitamin D.   Many people taking these steroids are warned about the risk of possible osteoporosis.  Persons taking weight loss drugs, and some cholesterol lowering drugs should also talk their doctor.