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The Role of Vitamin K2 in Bone Building & Osteoporosis

Causes of Bone Loss (Also see Health Benefits of Vitamin K2 Book and BONEGENESIS)

Bone is living tissue, with osteoclasts constantly breaking down old bone and osteoblasts building new. As people age the ratio of bone built to bone disassembled increases in favor of the latter. The interior of bone looks like a honeycomb in healthy people, but in osteoporotic individuals shows larger spaces due to bone being destroyed than is replaced. This makes bones weaker.

Experts do not fully understand why bone loss occurs. Many factors appear to contribute to this loss in fact. In women, drops in the level of sex hormones (estrogens) after menopause (Change-of-life) is widely deemed important player in bone loss. Other factors including genetic make-up and lifestyle factors such as diet, exercise levels and smoking also contribute to bone loss, as well as low body weight (< 58kg). A number of diseases and health challenges also increase the risk of developing osteoporosis such as rheumatoid arthritis, celiac disease and certain chronic lung diseases. In addition, certain medications, particularly cortisone or prednisone may also result in increased loss of bone

It was once believed that the major causes of osteoporosis were linked to low calcium intake and lower estrogen levels at menopause. This has not panned out. In cross-cultural analyses, one sees that many countries have lower calcium intakes than the US, yet osteoporosis is less prevalent in these countries. For example, the Japanese take in only 540 mgs calcium per day while Americans take in between 2 and 12 times this, yet the US hip fracture rate is twice that of Japan.

This paradoxical situation also appears to holds true for estrogen. Women all over the world experience declines in estrogen at menopause, but not all women experience osteoporosis. Therefore, attributing osteoporosis to natural declines in estrogen at menopause is too simplistic. In fact, the Mayan Indian, Bantu, and Japanese women all have lower estrogen levels than US women, but they all experience much fewer bone fractures than American women.

A more balanced or whole system perspective lends us to see osteoporosis as the outgrowth of a complex web of interacting bone-depleting factors, each building upon the other.

In diagnosing osteoporosis, the diagnostician endeavors to distinguish whether or not the case of osteoporosis at-hand is a primary problem or is secondary to another problem. To do this, a thorough history and physical examination is given, as well as appropriate diagnostic tests. It is important to distinguish primary from secondary causes because the treatments for these often differ.

Common causes of secondary osteoporosis include:

·         Endocrine disorders (such as hypogonadism, Cushing’s disease, hyperthyroidism, hyperparathyroidism, diabetes mellitus)

·         Marrow disorders (such as multiple myeloma, disseminated cancer, chronic alcohol use, lymphoma)

·         Collagen disorders (such as osteogenesis imperfecta, Marfans syndrome)

·         Gastrointestinal disorders (such as malabsorption, malnutrition)

·         Medications (such as aluminum antacids, anticonvulsants, chemotherapy, glucocorticoid therapy, thyroid hormone replacement)

Risk Factors for Osteoporosis

Approximately 10 million Americans (8 million women and 2 million men) have osteoporosis, and approximately another 13-17 million people have low bone mass, a condition that increases the risk of going on to develop osteoporosis.

Although the majority of folks with osteoporosis are women, osteoporosis is a problem for men too. The condition can affect people at any age regardless of ethnic background, but postmenopausal (and especially petite) women who are of Caucasian or Asian ancestry face a higher risk.

A woman’s risk of hip fracture is actually equal to her combined risk of breast, uterine, and ovarian cancer. The overall risk of developing osteoporosis is higher if any of the following are true:

• Being female and postmenopausal, and over the age of 50
• Being petite or having a small frame
• Having a family history of osteoporosis or bone fractures
• Having certain health conditions, such as low bone mass, anorexia, estrogen deficiency related to menopause, or amenorrhea  
• Use of certain medications, such as oral corticosteroids and anticonvulsants
• Lack of exercise, tobacco use, or heavy or binge alcohol use

There is actually no guaranteed sure method of determining the actual structure of bone short of removing a piece during a biopsy. Instead, the diagnosis of osteoporosis is based on special x-ray methods called densitometry. In densitometry MDs get accurate and precise measurements of the amount of bone, but not their actual quality. This measurement is called "bone mineral density" or BMD.

Bone density scanning, also called dual-energy x-ray absorptiometry (DXA or DEXA) or bone densitometry is an enhanced form of x-ray, which is the most accepted standard for measuring bone mineral density (BMD).

X-rays are a painless way to diagnose and treat medical conditions. Radiography involves exposing a part of the body to a small dose of ionizing radiation which essentially produces pictures of the interior of the body. X-rays are the oldest and most oft used form of medical imaging.

DEXA is usually performed on the lower spine and hips. Portable DEXA devices, including some that use ultrasound rather than x-rays, measure the wrist, fingers or heel and are sometimes used for screening purposes.

Vitamin K2 – especially MK-7 as a preventative & treatment

Vitamin K2 exerts a powerful influence on osteogenesis or bone building, especially in osteoporosis, and has been cited as one of the most frequently prescribed treatments for osteoporosis in countries like Japan.

Vitamin K is a family of structurally similar, fat-soluble, 2-methyl-l,4-naphthoquinones, including phylloquinone (K1), menaquinones (K2), and menadione (K3).  The "K" in vitamin K is derived from the German word "koagulation", which refers to blood clotting, something vitamin K is essential to via its influence on several proteins involved in blood clotting.

There are two naturally occurring forms of vitamin K – K1 and K2. Plants synthesize phylloquinone or vitamin K₁. Bacteria create a range of vitamin K forms, using repeating 5-carbon units in the side chain of the molecule which are designated menaquinone-n (MK-n --   n stands for the number of 5-carbon units). The MK-n family of menaquinones is collectively called vitamin K2 (such as Menaquinone-4, Menaquione-7, etc) M

The most common form of vitamin K2 in animals is menaquinone 4 (menatetrenone; MK-4), produced as the end result of the processing of exogenous and bacterial naphthoquinones. Vitamin K1 possesses a phytyl R group which is to say a partially saturated polyisoprenoid group, while K2 possesses a repeating, unsaturated trans-polyisoprenyl group.

Menadione (K3) is not considered a natural vitamin K, but a synthetic. Although menadione is a synthetic analogue, Billeter et al found that phyllo-quinone can be enzymatically processed by bacteria in the intestine to form a minor amount of menadione) After absorption, menadione is believed to become alkylated into biologically active isoprenylated menaquinones. However, vitamin K3 cannot exert all the functions of natural vitamin K because of limited transformation into fat-soluble forms of K.

Vitamin K is a cofactor in a number of biochemical pathways, the most common of which are vitamin K-dependent carboxylation reactions. In these reactions the reduced form of vitamin K (hydroquinone) de-protonates glutamate via the gamma-glutamylcarboxylase enzyme and forms an expoxide. The epoxide is recycled via vitamin K epoxide reductase, quinone reductase, and glutamic acid-containing proteins, such as coagulation factors II (prothrombin), VII, IX, and X, protein C, and protein S, are carboxylated. Compared to the other vitamin K analogues, vitamin K2 has the most potent gamma-carboxylation activity.

Vitamin K functions in the posttranslational modification of a number of vitamin-K dependent proteins such as osteocalcin, a bone protein containing gamma-carboxyglutamic acid. Gamma-carboxylation of the glutamic acid in osteocalcin is K-dependent and involves the conversion of glutamic acid residues (Glu) to gamma-carboxyglutamic acid residues (Gla). A number of calcium-binding proteins, such as calbindin and osteocalcin, contain gamma-carboxyglutamate, and are involved with calcium uptake and bone mineralization. Osteocalcin is synthesized exclusively in osteoblasts and  is regulated by the active form of vitamin D, 1,25(OH)2D3 or calcitriol

Unlike blood coagulation proteins, which require much lower levels of vitamin K for complete gamma-carboxylation, higher levels of vitamin K are essential for the total gamma-carboxylation of osteocalcin. The dietary intake of vitamin K in 219 healthy adults eating an average American diet was found to be inadequate for gamma-carboxylation of osteocalcin, while maintaining normal prothrombin time.

Another bone protein called Matrix Gla protein (MGP) is found in bone, cartilage, and soft tissue, including blood vessels.  Animal studies suggest MGP prevents the calcification of soft tissue and cartilage, while concomitantly facilitating normal bone growth and development. There is also the  vitamin K-dependent protein called anticoagulant protein S, which is also synthesized by osteoblasts. But evens o,  its role in bone metabolism is unclear. Children with inherited protein S deficiency suffer complications related to increased blood clotting as well as to decreased bone density

Requirements

The Daily Reference Intakes (DRI) for vitamin K is shown in the table below.

Life Stage            Vitamin K (mcg)

     0-6 months    2.0

     7-12 months 2.5

     1-3 years         30

     4-8 years         55

     9-13 years       60

     14-18 years    75

     19-30 years    120

     31-50 years    120

     51-70 years    120

     > 70 years       120

     9-13 years       60

     14-18 years    75

     19-30 years    90

     31-50 years    90

     51-70 years    90

     > 70 years       90

     < 18 years       75

     19-30 years    90

     31-50 years    90

     < 18 years       75

     19-30 years    90

     31-50 years    90

Dietary Sources

Vitamin K obtained principally from green leafy vegetables and some fruits. It may also be found in dairy products, meats and eggs.

Safety of Vitamin K2 with Respect to Excessive Coagulation

In a large number of clinical trials using dosages in excess of 40 mg/day, there were no reports of side effects associated with any kind of hypercoagulable state. Both animal and clinical studies indicate that vitamin K2 has no abnormal hemostatic activity. In one study, vitamin K2 given to rats at a dose of 250 mg/kg body weight per day for 10 days resulted in no substantive change in blood coagulation or platelet aggregation.

In one clinical study, 29 elderly, osteoporotic patients were given vitamin K2 (15 mg three times daily, 30 minutes after meals) for 12 weeks and monitored for any change in hemostatic balance. After 12 weeks, all hemostatic markers remained normal.  In another study which looked at the effect of vitamins K2 (45 mg/day) and D3 (1 mcg/day) on BMD in postmenopausal women, hemostatic measures were also explored. There were increases in both coagulation and fibrinolysis, but both remained within normal range and in balance, with no adverse reactions being noted.

This said, it should be pionted out that the anticoagulation drug warfarin, which prevents clotting by interfering with vitamin K, can have its effects offset with as little as 1 mg of vitamin K. Hence, use of vitamin K is contraindicated in people on anticoagulant therapy.

In Vitro Studies of Vitamin K2: Osteoblastic and Osteoclastic Modulation

Vitamin K2 has been shown to be the principle inducer of bone mineralization in human osteoblasts, while K2, in combination with 1-alpha-25-dihydroxyvitamin D3 has been shown to increase osteocalcin production. In vitro studies have shown that introduction of K2 results in gamma-carboxylation of 1-alpha-25-dihydroxyvitamin D3-induced osteocalcin, which in turn is then able to deposit gamma-carboxyglutamic acid-containing osteocalcin into the extracellular matrix surrounding human osteoblasts.

In vitro studies using assays from various animal species has shown that vitamin K2 inhibits osteoclastogenesis of bone. The osteoclastic inhibitory action by K2 is apparently unique to its structure.

Vitamin K1 does not affect bone resorption and multinucleate osteoclast-like cell formation. In vitro studies using mouse cell cultures found a dose-dependent inhibition by K2 of prostaglandin E2 (PGE2) synthesis, which in turn was shown to inhibit bone resorption. The inhibition of 1,25-dihydroxyvitamin D3-induced PGE2 production by K2 was found to be dependent on the inhibition of cyclooxygenase-2 expression. Studies using human bone marrow cell culture found evidence that the inhibition of osteoclast formation was not due to an increase in cell death, but rather to a decrease in the production of the receptor activator of nuclear factor kappa-B ligand (RANKL) and associated osteoclast differentiation factor, both of which are critical to osteoclastogenesis.

Animal Studies with Vitamin K2 in Rat Models of Disuse Osteopenia

As an outgrowth of animal studies, it was discovered that when rats were fed a vitamin K-deficient diet larger amounts of vitamin K were needed for femur bone metabolism compared to the liver.  The sciatic-neurectomized rat is often used as a model of immobilization osteopenia in people prevention of disuse osteopenia. This procedure reduces the normal maturation-related increase in cortical and cancellous bone, and thus leads to cortical and cancellous osteopenia. Orchidectomy results in a deficiency of testosterone, which in turn reduces periosteal bone formation, while concomitantly increasing cancellous bone turnover. This leads to inhibition of cortical and cancellous bone gain without net bone loss. Cancellous bone loss comes from decreased bone formation and increased bone resorption; whereas, cortical bone loss results from decreased periosteal bone formation and an increase in endocortical bone resorption.

In neurectomized rats, oral administration of vitamin K2 (10 or 30 mg/kg) for 7-42 days increased bone mass and maintained secondary spongia microstructure in the immobilized tibiae. In the animals given K2 30-mg/kg, trabecular number and thickness increased and osteoblast-induced mineralization was bolstered. By day 42, the osteoclast surface per bone perimeter, the number of osteoclasts per bone perimeter, and the mineral apposition rate (MAR) were reduced in the controls, suggesting bone turnover was suppressed. Low-dose vitamin K2 increased MAR and bone formation rate, and this increasing bone resorption. In this study, oral administration of vitamin K2 was found to reduce loss of trabecular bone, prevent osteoblast dysfunction, increase bone genesis rate, and preserve trabecular microstructure in an immobilization model.

When Vitamin K2 was given to orchidectomized rats (30 mg/kg) twice weekly for 10 weeks they evinced suppressed endocortical bone resorption and trabecular bone turnover. Vitamin K2 in sciatic-neurectomized and orchidectomized rats suppressed bone resorption and stimulated bone genesis. The evidence indicates that vitamin K2 has the potential to enhance bone formation and inhibit bone resorption in orchidectomized or neurectomized rats.

Animal (Rat) Model of Postmenopausal Osteoporosis

Estrogen deficiency results in increased bone turnover leading to an increase in bone-demolishing osteoclasts and trabecular bone loss. Postmenopausal osteoporosis, which is characterized by increased fracture risk, can be modeled using ovariectomized animals. Because ovariectomy in rats results in significant decrease of BMD and cancellous bone remodeling, it has been used as a model for estrogen-deficient, post-menopausal osteoporosis.

The administration of vitamin K2 has been shown to prevent bone loss induced by ovariectomy in rats, and at dose of 50 mg/kg inhibited the expected decreases in trabecular number and BMD of the femur, and improved other bone parameters caused by ovariectomy (And this in only a two-week period). In contrast, Binkley et al found no benefit in terms of bone turnover or distal femur BMD density in ovariectomized rats. This study used an K2 (50 mg/kg) for three months. The authors suggest these disparate results might be explained by three factors. First, the slight differences in vitamin D3- (2.4 IU/g in previous studies versus 2.2 IU/g by Binkley et al) and calcium-(0.02-0.5% in previous studies versus 1% by Binkley et al) deficient diets are proposed as one causative factor, which the researchers expressing their opinion that vitamin K may work best in calcium- and/or vitamin D-deprived rats. Second, the length of the study may have been a foactor with Binkley's being one month compared to Akiyama's two-week study. However, earlier studies found an effect after six months, which was undergirded by later studies that have shown a minimum of six months for effectiveness at a dosage of 30 mg/kg. (52,54) Despite the negative results of Binkley et al, more recent studies support earlier work that clearly demonstrated that vitamin K2 (30 mg/kg) for six months prevented bone loss and fragility of spine and femur in ovariectomized rats.

Ovariectomy is also considered a good model to demonstrate degeneration of the microarchitecture of bone associated with osteoporosis. Studies of the three-dimensional trabecular microarchitecture in ovariectomized and calcium-deficient rats fed vitamin K2 at30 mg/kg for eight weeks demonstrated a significant preservation of about 55% that of sham of trabecular bone volume, connectivity, and trabecular complexity. The protective effect of vitamin K2 on femoral strength and prevention of mechanical-strength decrease has also been supported by recent studies of ovariectomized rats. Ovariectomized rats given K2 at a dose of 30 mg/kg in combination with 1-25-dihydroxyvitamin D3 (0.3 mcg/kg three times weekly) orally for eight weeks demonstrated a significantly higher BMD, cortical thickness, and bone strength than rats given either of these vitamins alone.

Other Animal Studies With Regard To Vitamin K2 and Bone Preservation

Orchidectomized rats given subcutaneous vitamin K2 injections (30 mg/kg twice weekly) for eight weeks showed a significant increase in cancellous bone volume but not cortical area compared to orchidectomized rats not given K. The scientists concluded that vitamin K2 was more effective at preserving cancellous than cortical bone. In aged male rats, a calcium-deficient diet resulted in a 12-percent decrease in BMD, which was reversed by the administration of vitamin K2 at a dose of 30 mg/kg daily within eight weeks time.

The anti-epileptic drug phenytoin has been shown to induce bone loss, which has been linked to phenytoin's interference with vitamin D metabolism. In rats, decreased BMD in both diaphysis and metaphysis of femoral bones was thought to be due to reduced levels of vitamin K2 from administration of phenytoin. Vitamin K2 (30 mg/ kg daily) prevented BMD reduction from phenytoin (20 mg/kg subcutaneously) over five weeks.

Transgenic mice created to over-express granulocyte colony-stimulating factor [GCSF], which causes osteopenia and increased osteoclast number with a concomitant acceleration of bone resorption were given vitamin K2 at a dose of 0.05 mg/100 g in their chow (control group) or 20.0 mg/100 g in their chow (experimental group) for 12 weeks. The decreased bone mineralization was partially offset in the high vitamin-K consuming group.

Bone loss is one of the side effects of clinical corticosteroid use. The damage stems from a reduction in osteoblastic activity and bone formation. When prednisolone was given to lab animals (3 or 30 mg/ kg) along with vitamin K2 (15 mg/kg) for eight weeks, bone loss in trabecular bone was halted, though the K2 had no impact on loss of subcortical bone. These results complement earlier work on rats given prednisolone (7 mg/kg/day) for nine weeks along with vitamin K2 (17 mg/kg/day). This combination significantly inhibited the decrease in length, dry weight, and bone density of femurs and tibiae, and completely inhibited drops in urinary gamma-carboxyglutamic acid (Gla). Vitamin K2 (0.4, 10, and 50 mg/kg/day) significantly inhibited the loss of calcium content in the femur.

A number of human trials have found vitamin K2 effective in the treatment of osteoporosis In a randomized, open-label study, 241 osteoporotic women were divided up into 2 groups. 121 received 45 mg/day vitamin K2 and 150 mg elemental. 121 women in the 2^nd or control group took 150 mg elemental calcium daily. After two years, vitamin K2 was shown to maintain lumbar BMD. Those who took the K2 also experienced significantly lower fracture incidence (10% in the treatment group and 30% in the control group.) In a double-blind, placebo-controlled, 6 month study, eighty patients with osteoporosis received either 90 mg/day vitamin K2 or a placebo. Second metacarpal BMD was increased by 2.20 [+ or -] 2.48 percent compared to those who received placebo, which decreased by 7.31 [+ or -] 3.65 percent.

The incidence of osteoporosis is indisputably high in postmenopausal women. A number of studies have shown vitamin K2 can reduce bone loss in postmenopausal osteoporotic women. In one randomized controlled clinical trial, 172 osteoporotic/osteopenic women were assigned to receive vitamin K2 (45 mg/day), 1-alpha-hydroxycholecalciferol vitamin D3 (1 mcg/day), both, or placebo for a period of 6 months. The combination therapy resulted in a significant increase in BMD of ~5%, while vitamin K2 alone resulted in only a ~0.1% percent increase in BMD. However, BMD measured at 18- and 24-month intervals was significantly higher in the K2 group compared to the control group. In this study, a combination of vitamins K2 and D3 proved more protective than either supplement alone.

In another randomized study, ninety-two postmenopausal women (ages 55-81 years) were assigned to one of four groups: vitamin K2 (45 mg/day), 1-alpha-hydroxyvitamin D3 (0.75 mcg/day), a combination of vitamins K and D (same dosage as above), or calcium lactate (2 g/day). The vitamin-K and -D groups both experienced significant increases in BMD compared to the calcium group over a two-year period, while combined treatment was synergistic, significantly increasing lumbar BMD by 1.35 percent.

A number of bisphosphonate drugs such as etidronate, alendronate, and risedronate are prescribed to treat osteoporosis. These drugs appear to be more effective than vitamin K in increasing BMD, but may work better when employed with it. In one randomized, open-label study of 98 postmenopausal, osteoporotic women statistically significant decreases in fracture rates in 23 subjects taking vitamin K2 (45 mg/day) and 25 subjects (2/25) taking etidronate (200 mg/day for two weeks every three months) was shown, compared to 24 subjects taking calcium lactate (2 g/day). The fracture rate was lowered still further in 26 subjects taking a combination of vitamin K2 and etidronate.

Research of elderly populations has found a high incidence of hip fractures and osteoporosis in Parkinson's patients. This deficiency does not seem to be related to lack of 25-hydroxyvitamin D3, but instead to suppression of D3 by high serum calcium levels. The use of vitamin K2 was found to significantly increase 1,25-dihydroxyvitamin D3 and decrease serum calcium. In one study, Vitamin K2 (45 mg/day for 12 months) taken by 54 female osteoporotic Parkinson's patients (65 years or older) resulted in one hip fracture, compared to 10 fractures in 54 matched, untreated, osteoporotic Parkinson's patients. All hip fractures were caused by falls with no significant differences in the number of falls between groups. The average bone loss in the untreated group was 4.3 percent compared to 1.3 percent in age-matched controls. Vitamin K2-treated patients experienced an average 0.9 percent gain in BMD.

Long term use of glucocorticoids is one of the most common causes of drug-induced secondary osteoporosis.  A number of studies have found vitamin K2 to have a marked effect on the loss of BMD in prednisolone-treated patients. In one randomized study, sixty patients with chronic glomerulonephritis were assigned to four groups: 1-alpha-hydroxyvitamin D3 (0.5 mcg/day), vitamin K2 (45 mg/day), or vitamins K2 with D3 (CONTROL). Patients concomitantly took prednisolone (0.7 mg/kg) up to a maximum of 40 mg for four weeks then reduced this to 25 mg daily for another four. The control group experienced a significant decrease from baseline in BMD over the eight-week study.

Parallel results were seen in a randomized, prospective, controlled study of 20 patients with glomerulonephritis given 0.8 mg/kg/day prednisolone up to a maximum of 40 mg/day for four weeks, which was then reduced to 20 mg/day over a six-week period. One group received only prednisolone, while a second group was also given vitamin K2 (15 mg three times daily). After 10 weeks, a reduction in lumbar spine BMD was noted in the prednisolone-only group. The vitamin K2 group demonstrated a somewhat slower, rate of bone loss.

Anorexia is an eating disorder that produces weight loss, osteopenia, and osteoporosis that affects one percent of or so of American females. In one 11 month study, twenty-one patients diagnosed with anorexia were treated as follows: 10 patients were given vitamin K2 (45 mg/day) and 11 served as controls. The treatment group experienced significantly slower decrease in BMD compared to controls (-2.8% vs -6.9%, respectively). The levels of gamma-carboxyglutamic acid osteocalcin increased in the treatment group compared to controls (128.6% versus 28.3%, respectively).

Bone formation and bone loss involves a complex, sometimes interactive dance between nutrients and various molecular signals. A number of human studies have shown the potential of vitamin K2 for osteoporosis. Many studies have been carried out which confirm vitamin K2 efficacy for decreasing BMD from a variety of causes, including postmenopausal osteoporosis, Parkinson's disease, use of prednisolone, anorexia and more.

Vitamin K2 treatments are already in widespread use outside the United States.

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