**3.1 Vitamin D sources**

Vitamin D can be attained from foods as vitamin D3 (cholecalciferol) or as nutrient D2 (ergocalciferol). D3 is acquired from animal sources, while D2 is available in parasites and mushrooms irradiated with UVB [7]. Vitamin D approximate content in various foods is shown in **Table 1** [8].

Since most foods contain low measurements of vitamin D (**Table 1**), fortifying common foods is becoming a trend and common practice nowadays. In addition, nutritional supplements are a reliable solution for compensation of the vitamin deficiency [4].

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*Nutritional Considerations of Vitamin D Deficiency and Strategies of Food Fortification*

Milk 0.8–1.3 Margarine 8–10

Butter 0.3–2 Milk <1 Cheese < 1 Liver 0.5–4 Fish 5–40

**Food Approximate vitamin D content (μg/100 g)**

The Food and Nutrition Board has set an adequate intake (AI) for vitamin D due to the inability to set a more precise RDA level because of the variability in sun exposure among individuals [9]. Recommendations for vitamin D instructed an AI for vitamin D of at least 500 IU/day (12.5 μg) and more than 1000 IU/day (25 μg)

International units are used to quantify vitamin D. 1 IU is equal to 25 metric weight unit of cholecalciferol, and 1 g of cholecalciferol is equal to 40 IU [7].

Metabolism of vitamin D occurs through different stages that includes hydroxylation. Through these stages, vitamin ingested is transformed into its active form

Vitamin D synthesis starts when 7-dehydrocholesterol (cholesterol precursor found on skin) is visible to sunlight and then transformed to previtamin D [9, 10]. 7-Dehydrocholesterol is an intermediate precursor for vitamin D, it is found throughout the epidermis and dermis, and thus has the most elevated limit with

The first step occurs when 7-dehydrocholesterol absorbs the UVB photons to convert them into previtamin D3. Then, photoisomerization occurs in order to covert previtamin D3 into vitamin D3 (cholecalciferol). However, it is not a problem since during delayed sun exposure previtamin D3 is converted into its inactive

Large portion of vitamin D reaches liver from lipoproteins or vitamin D–binding protein and is then transformed by hydroxylation to yield 25-OH-D3 [4]. 25-OH-D3 is the major circulating type of vitamin D used by clinicians to evaluate vitamin D level, though it is latent and must be transformed to its active form (1α,25-

When calcium decreases in the body, parathyroid hormone is released leading to calcitriol synthesis increase (vitamin D active form: 1α,25(OH)2D) (**Figure 3**). Because of the hypocalcemia (declined blood calcium), PTH is released from parathyroid gland resulting in an increase in the hydroxylation of 25(OH)D3 to calcitriol. Then, calcitriol plays its role with PTH or by itself on its target tissues leading to an increase in serum calcium levels. Kidneys, bones, and intestines are the primary target tissues [8]:

*DOI: http://dx.doi.org/10.5772/intechopen.89612*

Fortified

Nonfortified

**Table 1.**

**3.2 Vitamin D needs and normal levels**

*Major food sources of vitamin D [8].*

for those not exposed to enough sunlight [8].

**3.3 Metabolism and regulation**

respect to cholecalciferol synthesis [11].

forms (lumisterol and tachysterol) [12].

dihydroxyvitamin D) in the kidneys [13].

(**Figure 2**) [4].

*Nutritional Considerations of Vitamin D Deficiency and Strategies of Food Fortification DOI: http://dx.doi.org/10.5772/intechopen.89612*


**Table 1.**

*Vitamin D Deficiency*

nervosa [1].

daily [1].

*2.3.1 Fat-soluble vitamins*

*2.3.2 Water-soluble vitamins*

**2.4 Vitamin deficiencies**

and dementia

**3. Vitamin D**

teeth health [4].

deficiency [4].

**3.1 Vitamin D sources**

content in various foods is shown in **Table 1** [8].

Vitamins A, D, E, and K are fat-soluble. They remain inside the fatty parts of

Fat-soluble vitamins include the B vitamin and ascorbic acid (vitamin C). They are distributed in many foods. Water-soluble vitamins are absorbed easily via the enteral tract straight into the blood and then into the cells. Water-soluble vitamins are not stored in large amounts, except vitamin B12. Thus, they should be eaten

Vitamin deficiency is the condition of a long-term lack of a certain vitamin.

• Vitamin A, which leads to vision defect, impaired growth, and immunity

• Vitamin B12, which leads to pernicious anemia, nerve damage, memory loss,

• Vitamin C, which mainly leads to Scurvy disease, fractures, and depression

Vitamin D, known as the sunshine vitamin, is a real hormone delivered from body's sterols by the photolytic activity of UV light on the skin [4]. It is a fat-soluble seco-steroid that may be either created within the skin from its precursor (7-dehydrocholesterol) by exposure to sunlight or offered from diet [5, 6]. Vitamin D with calcium, magnesium, and phosphorus plays a crucial role to support bones and

Vitamin D can be attained from foods as vitamin D3 (cholecalciferol) or as nutrient D2 (ergocalciferol). D3 is acquired from animal sources, while D2 is available in parasites and mushrooms irradiated with UVB [7]. Vitamin D approximate

Since most foods contain low measurements of vitamin D (**Table 1**), fortifying common foods is becoming a trend and common practice nowadays. In addition, nutritional supplements are a reliable solution for compensation of the vitamin

Most common and serious vitamin deficiencies are as follows [1]:

• Vitamin D, which leads to rickets, osteomalacia, or osteoporosis

• Vitamin K, which leads to coagulopathy and bone health impacts

foods and are absorbed along with dietary fat. Fat-soluble vitamins have good storage in the body since they are kept in the adipose tissues. Fat-soluble vitamin toxicity symptoms include hair, skin, bones, eye injuries, and anorexia

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*Major food sources of vitamin D [8].*
