We all know that vitamin D is critical for bone health. We have been supplemented with vitamin D and calcium all our life. Nowadays, many vitamin D supplements available in pharmacies contain vitamin K2 along with calcium. Most people have little to no idea of what vitamin K2 is, its significance for our body, why do we need K2 with vitamin D, and why K2 not K1. In this blog, I’m going answer all these questions. So, let’s get started:
Why do we need vitamin D?
Vitamin D is a fat-soluble vitamin that requires fatty-rich food to absorb in the body. It is produced in the skin upon exposure to direct sunlight. The sun rays convert cholesterol under the skin into a precursor of vitamin D. The precursor vitamin D metabolite undergoes two successive hydroxylations (addition of hydroxyl ion) in the liver (25-hydroxyvitamin D or calcidiol)) and kidney (1,25-dihydroxy vitamin D or calcitriol) for conversion to vitamin D. The chemical name of the vitamin D is calciferol.
Vitamin D boosts immunity, is essential for developing and maintaining healthy bones and teeth, optimizes brain health, and controls inflammation. Also, vitamin D facilitates the absorption of calcium from the intestines.
What is vitamin K2 and its significance for human body?
Vitamin K2 is a fat-soluble vitamin, found in fermented foods, and animal products. It’s also produced by the gut microbiome. It is different from vitamin K1, found abundantly in green leafy vegetables. The vitamin K2 helps blood clotting and is therefore known as a Koagulation vitamin in Danish.
An adult requires a daily dose of 90-120 μg/day to prevent its deficiency. The vitamin K is absorbed through the intestine and reaches the liver through circulation, where it is used to form several clotting factors (proteins). Significant quantities of vitamin K2 are utilized by the liver, leaving fewer quantities for the bones and cartilage; therefore, supplementation of K2 is essential.
Also, it maintains bone health, protects the heart, prevents calcium deposition in the soft tissues such as arteries, increases insulin sensitivity, lowers blood sugar, and delays the onset of diabetes.
A brief overview of bone composition
The bones comprise an inorganic matrix (60-70%) of hydroxyapatite crystals (calcium, phosphate and 10 other minerals), which give firmness and hardness to them. The organic matrix (30-40%) is rich in collagen (80-90%), a fibrous protein, which makes it elastic and flexible to bear the physical insults. The small percentage of non-collagenous proteins (10-15%), such as osteocalcin and matrix Gla proteins (MGP), contribute towards mineralizing the bones.
Why do we need K2 with vitamin D?
A bone undergoes remodeling throughout the life. The remodeling is when the older bone is removed and replaced by a new one. An equilibrium between bone resorption and deposition maintains the thickness and density of the bones. Vitamin D, along with K2, maintains bone turnover, regulates calcium, and prevents its deposition in the arteries.
Osteoporosis is a disease where bones lose mass and become weak and brittle. K2 supplementation with calcium and vitamin D can reverse osteoporosis seen in obese people and post-menopausal women; vitamin K2 modulates the activity of bone-forming and resorbing cells.
In the bones, bone-forming cells (osteoclasts) produce two vitamin K-dependant proteins, i.e., osteocalcin and matrix Gla protein (GLA). Vitamin K dependant proteins are calcium ion-binding proteins/molecules that become functional when they bind to vitamin K2, so vitamin K2 enables them to function.
These proteins help in bone mineralization. For instance, Osteocalcin has one domain or end that binds to collagen, and the other end binds to calcium in hydroxyapatite crystals in the bone and locks calcium in the bones. Vitamin K activates the calcium-binding site of osteocalcin by removing hydrogen ions from it, making it negatively charged and increasing its affinity for the positively charged calcium ions.
The calcium and vitamin D supplements were primarily used for bone health, but due to the risk of calcification in the arteries, clinicians were looking for a safer alternative. Clinical studies show that adding K2 to calcium and vitamin D supplements resulted in a 35-40% reduction in bone loss at the femoral neck (neck of the thigh bone) with improvement in bone mass in post-menopausal women. It also reduces the risk of spinal (60%), non-spinal (80%) and hip fractures (77%). Vitamin K2 stops calcium deposition in the arteries and protects the heart and brain from heart attack and stroke.
Why do we need K2 not K1 with vitamin D
Two biologically active forms of vitamin K occur in nature: vitamin K1 or phylloquinone and vitamin K2 or menaquinones. However, both have standard ring structures called 2-methyl-1, 4-naphthoquinone. Their dissimilarities make them favorable for a particular body function. As described earlier, K1 is abundant in plant-based foods, especially green leafy vegetables, and K2 in animal products.
Both vitamin K1 and K2 can activate vitamin K-dependent proteins. However, vitamin K2 performs better because of the following reasons:
- Higher hydrophobicity: Vitamin K2 is long chain molecule with higher fat solubility than K1. The higher fat-solubility allows it to cross the cell membrane more efficiently.
- Higher affinity for enzyme involved in the activation of vitamin K dependant proteins: Vitamin K2 has higher affinity for γ-glutamyl carboxylase (an enzyme) than K1 which is required for activation of vitamin K dependant proteins.
- longer half-life: The vitamin K2 stays in the body for a couple of days, whereas K1 is eliminated within 8 hours.
- Distribution: Vitamin K1 is stored in the liver whereas K2 is widely distributed in the body.
How to get K2 from diet?
The following foods are rich in vitamin K2:
- Fermented foods such as natto and Sauerkraut
- Eggs
- Sour milk such as buttermilk, yougurt or kefir
- Cheese (hard, semi-solid and soft)
- Fish like eel and plaice
- Organ meats such as liver and kidney.