Vitamin D molecule (http://www.vitaguide.org)

Vitamin D:  Steroid hormone vitamin;

Five forms of vitamin D discovered – D₁–₅.

Two forms matter most to humans: Vitamins D₂ (ergocalciferol) and D₃(cholecalciferol).

The active form of vitamin D in the body is called Calcitriol (1,25-Dihydroxycholecalciferol).
Calcitriol: promotes the absorption of calcium and phosphorus from food in the gut and reabsorption of calcium in the kidneys – this increases the flow of calcium in the bloodstream. This subsequently increases bone formation and healthy mineralization.  This prevents hypocalcemic tetany àlow calcium condition in which patients have overactive neurological reflexes, spasms of the hands and feet, cramps and spasms of the voice box (larynx). Calcitriol also plays a key role in the maintenance of many organ systems.

The Good.

Vitamin D had been implicated in the following.

.    and more…

We know about 5 forms of vitamin D, of which vitamins D₂and D₃ are the major forms as far as humans are concerned. They are known collectively as calciferol.

·         Vitamin D₂, ergocalciferol (made from ergosterol).
It is produced by invertebrates (animals without a spine, vertebral column), fungus and plants in response to sunlight (UV irradiation). Humans and other vertebrates do not produce vitamin D₂. We don’t know much about what vitamin D₂ does in invertebrates. We know that ergosterol is a good absorber of ultraviolet radiation which can damage DNA, RNA and protein; consequently many scientists believe it may serve as sunscreen that protects organisms from sunlight damage.

Vitamin D Metabolism (http://2.bp.blogspot.com)

·         Vitamin D₃, cholecalciferol (made from 7-dehydrocholesterol).
Vitamin D₃ is made in the skin when 7-dehydrocholesterol reacts with ultraviolet light at
270-300 nm wavelengths – peak vitamin D₃production occurs between 295-297 nm. It is only when the UV index is greater than 3 that these UVB wavelengths are present.

A UV index of more than 3 occurs every day in the tropics. In Canada, we have this mainly during some of spring, all of summer, and parts of autumn.  The number of days of the year when the UV index is greater than 3 decrease the further you move away from the tropics.

Both D₂ and D₃ are used in human nutritional supplements. Pharmaceutical forms include calcitriol (1alpha, 25-dihydroxycholecalciferol), doxercalciferol and calcipotriene. The majority of scientists state that D₂ and D₃ are equally effective in our bloodstream. It is believed that D₃ is more effective for humans.

For maximum Vitamin D creation during the summer months it is recommended that we expose unprotected skin to two sessions of 15 minutes of sunlight each week.  Our body will naturally produce adequate amounts of vitamin D. The following factors may reduce your body’s vitamin D synthesis:

If you can’t produce enough vitamin D due to insufficient sunlight exposure you will need to obtain it in foods and perhaps supplements.

Of course the recommendation for 15 mins of unprotected sun exposure does increase a persons’ risk for skin cancer.  Therefore, you have to use your judgement and make an educated choice for yourself.  For instance, my goal is to have 10-15 mins of unprotected sun exposure on my face, arms and neck (occasionally chest or back) during the summer months, not during peak sun hours (i.e. 1300 – 1700) twice per week in order to get adequate.  The rest of the time in the sun, PROTECTION (i.e. sunscreen or clothing).  I am hoping to get my vitamin D levels measured just before summer and then again after summer to see the effect.  Unfortunately, at this time in Canada, Vitamin D blood work is not covered by OHIP, so I’ll have to pay the $40 or so (x 2).

Well worth it though, seeing as how prevalence of Vitamin D deficiency are widespread in temperate areas.  The NHANES survey (USA) found that 9% (7.6 million) of children, were vitamin D deficient (defined as less than 15 ng/mL of blood), while another 61 percent, or 50.8 million, were vitamin D insufficient (15 to 29 ng/mL). This finding was shocking to health professionals across the US.

Those at high risk of vitamin D deficiency should consume 25 μg (1000 IU) of vitamin D each day to insure a good level of 25-hydroxyvitamin D in the bloodstream. Elderly people, as well as those with dark skin should consume extra vitamin D for good health.

According to the Food Nutrition Board at the Institute of Medicine of The National Academies, which created the Dietary Reference Intakes (DRIs), people should be getting the following amounts of vitamin D if nothing is being synthesized (inadequate sunlight exposure):