1. Significance and sources of vitamin D
Domina Petric, MD

2. Significance of vitamin D
Vitamin D, the sunshine vitamin, is actually a hormone produced from sterols in the body by the photolytic action of ultraviolet light on the skin.
Individuals who receive modest exposures to sunlight are able to produce their own vitamin D.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

3. Significance of vitamin D
Vitamin D plays an important role, along with the essential minerals calcium, phosphorus, and magnesium, in the maintenance of healthy bones and teeth.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

4. Significance of vitamin D
Metabolic bone diseases target women, who are more susceptible to osteoporosis than are men.
Starting during the fourth or fifth decade of life, both men and women lose bone mass at similar annual rates.
After the onset of menopause, the rate of bone loss in women can increase as much as tenfold owing to diminished production of estrogen, which is required along with vitamin D to maintain bone mineralization.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

5. Sources of vitamin D
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

6. Distribution in foods
Ergocalciferol and its precursor ergosterol are found in plants, fungi, molds, lichens and some invertebrates (snails and worms).
Cholecalciferol is widely distributed in animals, in which its provitamin D form, dehydrocholesterol, is a normal metabolite, but has an extremely limited distribution in plants.
In animals, tissue cholecalciferol concentrations are dependent on the vitamin D content of the diet and/or the exposure to sunlight.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

7. Distribution in foods
The richest natural sources of vitamin D3 are fish liver and oils.
In plants Solanum glaucophyllum, Solanum malacoxylon, Cestrum diurnum and Trisetum flavescens, the vitamin occurs as water-soluble β-glycosides of vitamin D3:
25-hydroxyvitamin D3 (25-OH-D3) and 1,25- dihydroxyvitamin D3 (1,25-[OH]2-D3).
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

8. Food fortification
Both vitamers D2 and D3 are used in the fortification of foods.
Multivitamin supplements typically contain 400 IU of vitamin D.
Pharmaceutical preparations can contain as much as 50,000 IU vitamin D2 per capsule/tablet.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

9. Vitamin D activities in foods
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

10. Herring: 330 IU/100 g Herring liver oil: 140,000 IU/100 g
iStockPhoto.com
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

11. Cod: 85 IU/100 g Cod liver oil: 10,000 IU/100 g
Wikipedia.org
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

12. Salmon: 220-440 IU/100 g Foodnetwork.com
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

13. Sardines: 1,500 IU/100 g Manettas.com.au
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

14. Shrimp: 150 IU/100 g Seriouseats.com
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

15. Poultry skin: 900 IU/100 g 21food.com
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

16. Other, less significant sources:
Butter
Cheese
Cream
Eggs
Beef liver
Chicken liver
Pork liver
Beef
Pork
Poultry
Cabbage
Corn oil
Spinach
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

17. Biosynthesis of Vitamin D3
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

18. Biosynthesis of Vitamin D3
Vitamin D is formed in animals by the action of ultraviolet (UV) light (295–300 nm) on dehydrocholesterol in the skin.
The activation reaction depends on the absorption of UV light by the 5,7-diene of the B ring of the sterol nucleus, causing it to open and isomerize to form the energetically more stable s-trans, s-cis- previtamin D3.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

19. Biosynthesis of Vitamin D3
The provitamin D sterol, 7-dehydrocholesterol, is both a precursor to and product of cholesterol (via different pathways).
It is synthesized in the sebaceous glands of the skin.
It is secreted rather uniformly onto the surface, where it is reabsorbed into the various layers of the epidermis.
The skin contains very high concentrations of the sterol (200 times that of liver).
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

20. Biosynthesis of Vitamin D3
In humans, the greatest concentrations of 7-dehydrocholesterol are found in the deeper Malpighian layer (stratum basale, stratum spinosum).
Wikipedia.org
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

21. Biosynthesis of Vitamin D3
Holick has estimated that exposure to the median erythemal dose of sunight can produce 10,000 to 25,000 IU of vitamin D.
He recommends exposures of one-quarter of that amount of sunlight two to three times weekly to support the synthesis of physiologically relevant amounts: 15,000 IU per week.
Holick, M. F., and Jenkins, M. (2003). The UV Advantage, ibooks, New York, p. 93
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

22. Biosynthesis of Vitamin D3
Dark-skinned individuals appear to require longer UV doses than light-skinned individuals for comparable vitamin D biosynthesis.
Both the thickness and 7-dehydrocholesterol content of skin decline with age.
The vitamin D biogenic response to solar irradiation is diminished in older people.
An age-related decline in plasma 25-OH-D3 concentration is typically seen in individuals without significant dietary intakes of the vitamin.
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

23. Literature
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc
9/22/2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc