ALL YOU NEED TO KNOW ABOUT VITAMIN K
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Following Rachel’s blog post entitled “Crunchy Kale”, I thought it would be nice to go into a bit more depth about vitamin K, as kale is one of its best sources.
What is vitamin K?
Vitamin K is a fat-soluble vitamin, meaning that the body stores it in fat tissue and in the liver. There are two forms of vitamin K: vitamin K1 and vitamin K2.
Vitamin K1 is found in plant foods such as kale, spinach and broccoli, as well as vegetable oils such as olive oil, canola oil and soyabean oil. Vitamin K2 is modestly found in liver, meat, eggs, high-fat dairy from grass-fed cows and fermented foods such as natto, miso and sauerkraut. Almost the whole vitamin K2 family is produced by our gut bacteria, meaning that it’s incredibly important for our gut to be healthy.
Although data on vitamin K’s bioavailability (the amount of vitamin K your body absorbs and utilises) from different food sources are scarce, it is suggested that certain fermented foods and hard cheeses may have greater absorption rates than leafy greens.
Why is vitamin K important?
Vitamin K is traditionally recognised as an important factor for blood clotting because it activates certain liver proteins. However, research has revealed that vitamin K may also play a crucial role in maintaining strong bones, regulating cell growth and preventing calcium deposits in blood vessels; a risk factor for heart disease.
How much vitamin K do I need?
Even though there isn’t sufficient data to establish recommended dietary intakes (RDAs) for vitamin K, there are adequate intakes (AIs) that are based on vitamin K intakes in healthy group populations. Below is a table of AIs for all age groups in South Africa.
| μg/day | |
| Age | Males and Females |
| 0-6 months | 2 |
| 7-12 months | 2.5 |
| 1-3 yrs | 30 |
| 4-8 yrs | 55 |
| 9-13 yrs | 60 |
| 14-18 yrs | 75 |
| 19+ yrs | 90 |
| Pregnancy and Lactation | |
| <18 yrs | 75 |
| 19-30 yrs | 90 |
| 31-50 | 90 |
Table 1 – Adapted from The Nutrition Information Centre of the University of Stellenbosch. Adequate Intakes (AIs) of vitamin K for different age groups.
Vitamin K deficiency
The only clinically-significant indicator of vitamin K status is the time it takes for blood to clot. Vitamin K status is not assessed routinely unless you take blood thinners such as Warfarin. Antibiotics can also have a profound effect on vitamin K status because they destroy the gut bacteria that produce vitamin K. Therefore, it is important to be aware of your vitamin K intake when taking antibiotics or if you take blood thinners. People who take antibiotics might need to increase their intake of vitamin K, while those who take anticoagulants are required to maintain a consistent intake as abrupt changes can increase or decrease the blood thinning effect.
Vitamin K deficiencies are quite rare in adults, but more common in newborns. That’s why newborns controversially receive a vitamin K injection. In adults, vitamin K deficiency is more limited to people who take medication that reduces the amount of fat your body absorbs, or people who have a gut malabsorption disorder, such as Crohn’s disease. In these cases, your doctor or other health practitioner might suggest some form of supplementation. Bleeding and haemorrhaging are typical signs of vitamin K deficiency; however these symptoms only happen in severe cases. Vitamin K deficiency can also reduce bone density and contribute to osteoporosis.
Vitamin K food sources
Below is a table with some selected food sources for both vitamin K1 and vitamin K2.
| Food | μg per serving |
| Natto (85g) | 850 |
| Spinach, raw (1 cup) | 145 |
| Kale, raw (1 cup) | 113 |
| Broccoli | 110 |
| Soy beans, roasted (1/2 cup) | 43 |
| Carrot juice (3/4 cup) | 28 |
| Soybean oil (1 Tbsp) | 25 |
| Pomegranate juice (3/4 cup) | 19 |
| Pine nuts, dried (28g) | 15 |
| Blueberries, raw (1 cup) | 14 |
| Chicken breast, cooked (85g) | 13 |
| Canola oil (1 Tbsp) | 10 |
| Olive oil (1 Tbsp) | 8 |
| Ground beef, cooked (85g) | 6 |
| Chicken liver, cooked (85g) | 6 |
| Cheddar cheese (14g) | 4 |
| Egg boiled (large) | 4 |
| Milk 2% (1 cup) | 2 |
Table 2 – Adapted from the Vitamin K Fact Sheet for Health Professionals from The National Institutes of Health. Selected vitamin K1 and K2 food sources
As you can see, it’s pretty easy to meet your requirements as there are several food sources that provide vitamin K. Rachel included some easy and tasty recipes using kale or spinach in her blog post. Have a read and give them a try!