Vitamin K1 is the main form of this fat-soluble found widely in green leafy vegetables, especially those if the cabbage family. Beans, kale, collards, spinach, broccoli, brussel sprouts, asparagus, prunes, green peas, blueberries, and carrots are all good sources of vitamin K1. After ingestion, the normal gut bacteria, Escherichia coli and Bacillus subtilis that are part of the normal human microbiome, transform K1 into K2, the main storage form in humans. K2 is absorbed into the body and stored in the fat tissues until needed. K2 is sold and promoted as a bone supplement in the US. The U.S. Food and Drug Administration has not approved any form of vitamin K for the prevention or treatment of osteoporosis. K2 is approved for treatment of osteoporosis by Ministry of Health in Japan since 1995.
Vitamin K Treatment of Osteoporosis in Japan
In Japan, where Vitamin K2 is registered with their FDA, the Ministry of Health, for treatment of osteoporosis the recommended dose is 45 mg per day. Studies there showed this was the minimally effective dose for having a small beneficial effect on bone density of the lumbar spine. It is not proven conclusively that K2 prevents fractures. In Japan, it is most commonly used in combination with alendronate. In several small studies, women on alendronate plus K2 had a better improvement in DXA bone density than those on vitamin K2 or alendronate alone. In Japan, the preferred therapy is use of activated vitamin D3, not available here that is added to alendronate or K2 or both.

Osteoporosis Seen in Asian People is Different than the Osteoporosis Seen in People Descended from Northern Europeans
It is important to understand that Japanese people do not have the same primary cause for osteoporosis seen in people of Northern European ancestry. Virtually all the research on K2 has come out of Asia most from Japan performed on postmenopausal Asian women. What works for Japanese or other Asian people with osteoporosis may not work in white people of Northern European Ancestry because their version of osteoporosis, while superficially similar, has very different causes and genetic underpinnings.

Recommended Dietary Intake and Sources for Vitamin K
The recommended dietary intake for vitamin K1 is 120 ug per day. There are 1,000 ug in 1 mg so you can see that the body needs only a tiny amount of K1 daily to meet the health parameter set for it by the Institute for Medicine that decides this today in the US. They base their decision for K1 on the dose needed to ensure that the average person is able to clot their blood adequately. K1 is used as a cofactor by the enzymes that make clotting factors. When K1 is deficient; the activity of clotting factors diminishes resulting in bleeding. There is no recommended daily intake for vitamin K2.

In bone, K2 is a needed cofactor for the production of osteocalcin; non-collagenous protein secreted by osteoblasts that plays a role in the formation of mineral in bone. K2 is synthesized by animal tissues and is found in meat, eggs, and dairy products. K2 is often found in relatively small quantities in meat and eggs. K2 is synthesized by bacteria during fermentation and is found in fermented soybeans and in most fermented cheeses. The richest source of natural K2 is the traditional Japanese dish natto made of fermented soybeans by Bacillus subtilis, but there is only 1 mg in 100 gm of natto and that is a lot of natto. Natto is served as a condiment in Japan, on the side in tiny dishes in small amounts to flavor other dishes. No one would eat 100 Gms of natto at one time. It is not possible to get dietary enough K1 or K2 from any diet anywhere to obtain an adequate quantity to treat osteoporosis using the recommendations issued by the Ministry of Health in Japan of 45 mg daily. It is alleged that consumption of Natto in Northern Japan has been linked to significant improvement in vitamin K status and bone health in many studies but the reliability of this data is clearly suspect when one considers the facts. The intense smell and strong taste of natto while beloved in Japan make this soya food a less attractive source of K2 for Westerners’ tastes. Supplement food companies sell nattō extract, standardized for K2 content, in capsules. For those interesting in using this supplement, that approach makes most sense.

Osteocalcin is secreted solely by osteoblasts and is associated with bone formation. It plays a role in bone mineralization and calcium homeostasis. Osteocalcin acts as a hormone in the body, causing beta cells in the pancreas to release more insulin, and at the same time directing fat cells to release the hormone adiponectin, which increases sensitivity to insulin. Osteocalcin acts on Leydig cells of the testis to stimulate testosterone biosynthesis. Osteocalcin also acts on myocytes to promote energy availability and utilization and in this manner favors exercise capacity.

Use as a Biochemical Marker for Bone Formation
As osteocalcin is produced by osteoblasts, it is often used as a marker for the bone formation process. It has been observed that higher serum-osteocalcin levels are relatively well correlated with increases in bone mineral density on DXA testing of patients treated with Forteo a bone-building drug.

K2 is Not Toxic
K2 has not been shown to be toxic unlike the other fat-soluble vitamins. It is not stored in the liver and that may explain why. I do not recommend people use K2 for treatment of osteoporosis but if I did, I would keep the dose at the 45 mg per day level approved by the Ministry of Health in Japan.