Vitamin D
What is Vitamin D?
Vitamin D is a fat-soluble steroid prohormone. The term Vitamin D refers to two molecules, ergocalciferol (D2) and cholecalciferol (D3). Cholecalciferol is the most effective form of Vitamin D and is manufactured in the skin by the action of ultraviolet radiation on 7-dehydrocholesterol.
Dietary ergocalciferol and cholecalciferol are biologically inactive and are activated to 25-hydroxy Vitamin D in the liver. Further conversion in the kidney results in the production of the more active form 1,25-dihydroxy-vitamin D (calcitrol).
How do we get Vitamin D?
Sunlight exposure
- Major source of Vitamin D, providing the majority of the recommended 30 ng/mL daily dose of Vitamin.
- Vitamin D production is affected by seasonal changes, duration of exposure, sunscreen use and skin pigmentation.
Endogenous production
- Ability of skin and kidneys to form and process Vitamin D. Dietary intake.
- Minor source of Vitamin D, providing < 100 IU/day.
- Vitamin D is rare in foods other than fatty fish, eggs and supplemented dairy products.
- Even Vitamin D-fortified dairy products may not contain the level indicated on label.
- Vitamin D can be supplied by multivitamins and supplements.
- Patient compliance with supplementation therapy is inconsistent.
40 to 75% of the world’s population is Vitamin D deficient.
What function does Vitamin D serve in the body?
Vitamin D helps maintain healthy bones by promoting absorption of calcium and phosphorus, two key minerals needed for bones. Healthy bones reduce the incidence of fractures. Vitamin D is also required to maintain muscle strength, which helps prevent falls.
It is known that most cells express the Vitamin D receptor and about 3% of the human genome is directly or indirectly regulated by the vitamin D endocrine system. Vitamin D has a regulatory role for gene and receptors in cells.
Vitamin D levels are associated with:
- Immune system activity
- Prevention of certain cancers (e.g. colorectal cancer)
- Cardiovascular disease prevention
- Osteoarthritis
- Fetus development
- Risk for preeclampsia
- Insulin resistance
Why does low Vitamin D seem to be more prevalent today?
Oddly, as more people adopt healthy lifestyle changes they can be at risk for diminished Vitamin D. Those who follow strict plant-based diets may not get enough of the vitamin every day because they are not eating animal-based or fortified foods, and people who avoid sun exposure and use sunscreens are deprived of a dependable source of Vitamin D. The increase in aging population is also responsible for the higher prevalence of low Vitamin D. Senior citizens need higher intake to maintain optimal levels. Aging reduces the ability of the kidneys to convert Vitamin D to its active form, which increases risk for deficiency. Studies have shown that:
- Products which include a Sun Protection Factor of > 15 (i.e. sun screens like lotions, creams) limit the Vitamin D production of the skin as much as 99%.
- Skin pigmentation decreases the amount of Vitamin D production, i.e. darker skin colour is a limiting factor for production.
- Although deficiency is common, 25-hydroxy Vitamin D deficiency remains undiagnosed in most cases.
How do physicians measure Vitamin D levels?
The most accurate way to measure Vitamin D levels is the 25-hydroxy Vitamin D test. 25-hydroxy Vitamin D is the most prominent circulating form of Vitamin D and it is easily measured. 25-hydroxy Vitamin D is the body’s repository of Vitamin D and is established as the appropriate measurable indicator of Vitamin D status.
How do physicians treat patients with low Vitamin D levels?
Treatment for Vitamin D deficiency involves increasing intake of Vitamin D through diet, supplements, and spending more time in the sun. For a normal person to remain healthy, you need to maintain the level of 25-hydroxy Vitamin D in the range of 50 – 80 ng/ml year-round in your body.
Reference Range
| < 10 ng/mL | Deficient |
| 10 – 29 ng/mL | Insufficient |
| 30 – 100 ng/mL | Sufficient |
| > 100 ng/mL | Possible toxicity |
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