You may have heard of vitamin C or calcium when it comes to bone health. Still, there’s another nutrient that plays an important role: vitamin K. Vitamin K has several different forms, but vitamin K1 and K2 are naturally occurring forms.

This vitamin gets its name from the German word “Koagulationsvitamin,” which means “vitamin for blood coagulation.”
Excessive vitamin K does not raise the risk of blood clots, however, people who use warfarin (Coumadin®) for anti-coagulation should avoid taking supplemental vitamin K because warfarin is a vitamin K antagonist.

Vitamin K deficiency is related to osteocalcin under-carboxylation, osteopenia, and increased fracture risk, whereas vitamin K supplementation slows bone turnover and enhances bone strength.

Useful dietary sources of vitamin K

Vitamin K1 (phylloquinone) is found in plant foods and is the primary form of supplement available. Useful dietary sources of vitamin K include kale, collard greens, fresh spinach, Swiss chard, cabbage, Brussels sprouts, turnip greens, and parsley.
Vitamin K2 (menaquinones) is found in animal foods such as cheese and eggs or fermented soy (natto) and makes up a limited amount of the supplement market.

While both forms of vitamin K are necessary for human health, most people consume more than enough vitamin K1 in their diet. Vitamin K2 is the more elusive nutrient, but it is the more potent form when it comes to bone health.

Vitamin K and the gut

Different types of bacteria in our gut can synthesize menaquinones from plant-based precursors (phyllates), which are then absorbed into circulation. Because dietary intake alone cannot provide sufficient blood levels of menaquinones,
intestinal synthesis may contribute significantly to our total body pool.

The half-life in human plasma for menaquinones is longer than phylloquinone (~72 hours vs 30 hours), suggesting that once these vitamins are ingested they can be stored in body tissues and used over time.
For these reasons dietary intake or supplementation with either type of vitamin K may improve bone health by reducing osteoporosis risk. 

A large population-based study in Germany examined the relationship between intake of different nutrients including vitamins A, D, and K, and hip fractures among postmenopausal women.
Results showed that high intakes of vitamins D and A were associated with a significantly lower risk of hip fractures.

Vitamin chemistry and bone

Vitamin D works synergistically with vitamin K2 to promote bone health. A deficiency in either vitamin D or vitamin K2 can lead to problems with calcium metabolism and bone health, so it’s important to make sure you’re getting enough of both nutrients.
In contrast, high intakes of vitamins C and E showed no association with hip fracture risk.

Furthermore, when stratified by age group, only a high intake of vitamin D was associated with a significantly lower hip fracture risk among women aged 75 years or older. Interestingly, a 2 mcg/day increase in dietary intake of vitamin D was associated with a 22% lower risk of hip fracture.

These data suggest that adequate amounts of certain nutrients including vitamins A and D may help reduce the risk of osteoporotic hip fractures in postmenopausal women.

Furthermore, given the age-specific association between high intakes of vitamin D and decreased hip fracture risk, it appears that this benefit becomes more critical as we get older. 

Vitamin K and calcium

Vitamin K activates osteocalcin, a protein that helps bind calcium to bones and other tissues. When there is insufficient vitamin K, osteocalcin remains inactive and unable to perform its function properly.
This can lead to calcium deposits in soft tissues instead of bones, which increases the risk of fractures.

Vitamin K also inhibits the calcification of arteries by reducing levels of calcium in the blood.
This is important because high levels of calcium in the blood can lead to the hardening of the arteries (atherosclerosis), which can increase the risk of heart attack or stroke].

Conclusion

Vitamin K is an important nutrient for bone health and calcium homeostasis.
It helps to reduce the risk of osteoporotic hip fractures in postmenopausal women.

Vitamin D and vitamin K2 are both essential nutrients for bone health. A deficiency in either one can lead to problems with calcium metabolism and bone health. Foods rich in vitamin D include salmon, tuna, egg yolks, and fortified milk. Foods rich in vitamin K2 include natto, cheese, sauerkraut, and leafy green vegetables. Supplementing with both vitamins D and K2 can also help ensure adequate intake of these important nutrients.

If you are taking warfarin (Coumadin®), you should avoid supplemental vitamin K because warfarin is a vitamin K antagonist.


https://pubmed.ncbi.nlm.nih.gov/11269606/
https://pubmed.ncbi.nlm.nih.gov/18374202/
https://pubmed.ncbi.nlm.nih.gov/17274493/
https://www.science.org/doi/pdf/10.1126/science.99.2569.241.c?cookieSet=1