by Eleni Kalogirou
Vitamin K is a fat-soluble vitamin that exists in two main forms: Vitamin K1 (phylloquinone), which is the primary dietary form, and Vitamin K2, which consists of a group of menaquinones that are mainly of bacterial origin (synthesized primarily by intestinal bacteria).
Vitamin K and Blood Clotting
Vitamin K is also known as “the clotting vitamin,” as it serves as a key coenzyme in the synthesis of proteins involved in blood coagulation.
Its Role in Bone Health
Vitamin K also plays an important role in bone metabolism.
Vitamin K and Absorption
Compared to other fat-soluble vitamins, Vitamin K is metabolized and excreted very rapidly. As a result, the body retains only about 30–40% of the K1 consumed through food. Consequently, low levels of Vitamin K in the bloodstream and in the body’s stores are commonly observed, especially in cases of inadequate dietary intake.
Vitamin K can be obtained from both plant-based and animal-based foods. However, the primary form we consume is Vitamin K1, which is found in high concentrations in green leafy vegetables (especially spinach, kale, and broccoli), in plant oils, and in some fruits such as blueberries and grapes.
Menaquinones
Menaquinones (Vitamin K2) are mainly obtained through animal products such as chicken and beef. They are also present in fermented foods, such as cheese.
Examples of Foods and Their Vitamin K Content:
| Food | Quantity | Vitamin K (μg) |
| Natto (fermented soybean product) (as K2) | 3 ounces | 850 |
| Boiled turnip greens | 1/2 cup | 426 |
| Raw spinach | 1 cup | 145 |
| Raw kale | 1 cup | 113 |
| Boiled broccoli | 1/2 cup | 110 |
| Soybean oil | 1 tablespoon | 25 |
| Raw okra | 1/2 cup | 16 |
| Raw blueberries | 1/2 cup | 14 |
| Raw iceberg lettuce | 1 cup | 14 |
| Cooked chicken breast (as K2) | 3 ounces | 13 |
| Grapes | 1/2 cup | 11 |
| Dried cashews | 1 ounce | 10 |
| Raw carrots | 1 medium | 8 |
| Olive oil | 1 tablespoon | 8 |
| Cooked ground beef (as K2) | 3 ounces | 6 |
| Dried figs | 1/4 cup | 6 |
| Boiled egg (as K2) | 1 large | 4 |
| Salmon – Shrimp (as K2) | 3 ounces | 0.3 |
The recommended daily intake of Vitamin K aims to ensure normal blood clotting. Different organizations provide varying recommendations. Specifically, the U.S. National Academy of Medicine states that the adequate intake of Vitamin K is 120 μg for adult men and 90 μg for adult women per day.
On the other hand, the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) recommend 65 μg and 55 μg per day for men and women, respectively, based on an estimate of 1 μg per kilogram of body weight per day.
Below, we see the recommendations according to the U.S. National Academy of Medicine, expressed in micrograms per day:
| Age | Men | Women | Pregnancy | Breastfeeding |
| Birth to 6 months | 2.0 | 2.0 | ||
| 7–12 months | 2.5 | 2.5 | ||
| 1–3 years | 30 | 30 | ||
| 4–8 years | 55 | 55 | ||
| 9–13 years | 60 | 60 | ||
| 14–18 years | 75 | 75 | ||
| 19+ years | 120 | 90 | 90 | 90 |
How Does Vitamin K Enhance Bone Health and Bone Density?
Vitamin K affects bones in various ways. It is an essential coenzyme for the γ-carboxylation of certain proteins, including osteocalcin. Osteocalcin is one of the main proteins in bone tissue.
Vitamin K and Transcriptional Regulation
Vitamin K regulates the transcription of osteoblastic markers, osteoclast formation, and bone resorption.
Degree of Carboxylation and Bones
Research has linked the degree of osteocalcin carboxylation with bone density. Specifically, high levels of under-carboxylated osteocalcin have been associated with lower bone density.
Correlation Between Vitamin K Intake and Fractures
Some studies have connected higher Vitamin K intake with increased bone density and/or a reduced frequency of hip fractures. In a review, 12 out of 13 studies showed improved bone density with Vitamin K2 supplementation, and 7 out of 13 reported a reduction in fracture rates, especially in the hip and vertebrae. Overall, numerous published studies indicate that Vitamin K strengthens bone density and helps prevent bone deterioration and fractures.
Important Note
However, it should be noted that there is still insufficient data and recommendations are limited. Nonetheless, the positive effect of Vitamin K on bone health is undisputed, whether demonstrated to a lesser or greater extent by various studies.
Supplementation with Vitamin K is administered either through multivitamins, products containing 100% Vitamin K, or combined with calcium, magnesium, and/or Vitamin D. Some studies have shown reduced osteoporosis-related fractures after Vitamin K supplementation, while others have not shown the same results. Therefore, the benefit of supplements remains controversial and further research is needed.
Vitamin K and Calcium
Vitamin K combined with calcium may be a potential therapeutic strategy for improving bone mass.
Vitamin K as a Preventive Treatment
Due to limited data, health organizations do not currently recommend Vitamin K supplementation for osteoporosis prevention. For now, systematic consumption of Vitamin K-rich foods as part of a complete, balanced diet appears sufficient.
Vitamin K and Side Effects
On the other hand, taking Vitamin K supplements could cause problems for individuals on blood thinners or those at risk of thrombosis due to its clotting effect.
The possibility of supplementation should be considered for individuals with malabsorption syndromes, gastrointestinal disorders, or celiac disease, as absorption from foods might be reduced.
Include green leafy vegetables and nuts in your diet. Follow a varied and balanced diet incorporating all food groups. Remember, variety and good nutrition promote health! In this case, it certainly offers only benefits.
Over time, more data will emerge regarding the relationship between Vitamin K and osteoporosis. Until then, keep in mind its positive impact on bone health, but avoid taking supplements without professional advice and guidance.
Source: mednutrition.gr
