**2. Types of vitamin K**

Vitamin K refers to a family of compounds with a common chemical structure of 2-methyl-1,4-naphthoquinone (**Figure 1**) [14].

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*Relation between Vitamin K and Osteoporosis DOI: http://dx.doi.org/10.5772/intechopen.89656*

These compounds include:

1.Vitamin K1 (phylloquinone)

2.Vitamin K2 (menaquinones)

3.Vitamin K3 (menadione) [7]

Vitamin K1 (phylloquinone) comes from vegetables, especially green leafy

isoprenyl side chain (may range from 1 to 13 isoprene residues). The various menaquinones are generally denoted as MK-n, where n symbolizes the number of isoprene residues in the side chain and is designated as MK-4 through MK-13, established upon the length of their side chain. The most well-studied menaquinones are MK-4, MK-7, MK-8, MK-9, and MK-10 that all occur in the

Menaquinones (except MK-4) are of microbial origin, and relatively high concentrations are only found in a few food items. Natto (a traditional Japanese food made from fermented soybeans) has high amounts of menaquinones (almost exclusively MK-7). Other fermented foods, such as cheese, also contain menaquinones. However, the forms and amounts of vitamin K in these foods likely vary

Bacteria in the human gut produce most of the menaquinones, especially the long-chain menaquinones; the amount of vitamin K that the body acquires in this

Menadione is a synthetic form of vitamin K. It has increased toxic risk, so it is

In the intestine vitamin K is incorporated into mixed micelles, and it is absorbed

The AI for vitamin K1 is 120 mcg/day for men and 90 mcg/day for women as it

These current AI values are established upon the hepatic vitamin K demanded for activation of coagulation factor and absence of abnormal bleeding. There was not any DRI for vitamin K2 or an upper limit intake level for vitamin K1 at that time. Clinical trials have used vitamin K supplements at doses much higher than the DRI levels (10 mg for vitamin K1 and 45 mg for vitamin K2) and found no evidence of toxic effects. However, trials which have used supplements of 45 mg/day of MK-4

was determined by the Institute of Medicine in the United States in 2001 [17].

by enterocytes. From there, vitamin K is combined into chylomicrons, released into the lymphatic capillaries, transported to the liver, and then packed again into very-low-density lipoproteins. In the circulation, vitamin K is carried mainly in

Vitamin K2 (menaquinone) forms a subfamily in which it has an unsaturated

vegetables such as spinach, vegetable oils, broccoli, and some fruits [1].

relying on the strains of bacteria utilized to make the foods.

not a commonly supplemented form of vitamin K [1, 15].

demonstrate incidences of skin appendage lesions [18, 19].

**4. Absorption and transport of vitamin K**

**3. Sources of vitamin K**

human diet.

manner is unclear.

lipoproteins [16].

**5. Recommended intake**

**Figure 1.** *Structure of the main forms of vitamin K.*

*Relation between Vitamin K and Osteoporosis DOI: http://dx.doi.org/10.5772/intechopen.89656*

These compounds include:

*Clinical Implementation of Bone Regeneration and Maintenance*

ation of osteocalcin is mediated by vitamin K [10].

2-methyl-1,4-naphthoquinone (**Figure 1**) [14].

**2. Types of vitamin K**

Studies have reported that vitamin K plays a role in bone metabolism in other mechanisms. There is an evidence that vitamin K positively affects calcium balance and increase of calcium retention [9]. Vitamins K and D work synergistically on bone metabolism, the form of osteocalcin that osteoblasts produce is undercarboxylated osteocalcin, and this process is upregulated by vitamin D, while carboxyl-

Vitamin K is shown to decrease bone resorption by osteoclasts and inhibits production of bone-resorbing agents such as interleukin-6 [11] and prostaglandin E2 [12]. Osteoporosis is a metabolic bone disease of reduced bone density, fragile bone, and elevated susceptibility to fracture. Genetic factors, age, sex, race, general health, exercise, cigarette smoking, alcohol abuse, hormone replacement therapy, and nutrition are some of the factors that influence an individual's risk of osteoporosis [13]. The aim of the present paper is to summarize the present knowledge on vitamin K and bone metabolism, emphasize the role of vitamin K in bone health, and evalu-

Vitamin K refers to a family of compounds with a common chemical structure of

ate vitamin K as a diagnostic and therapeutic marker in osteoporosis.

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**Figure 1.**

*Structure of the main forms of vitamin K.*

