High daily dosages of vitamin K either from food or supplements are considered pretty safe. There hasn’t been established a maximum safe dose for healthy people.
What’s the recommended daily intake?
The recommended daily intake of vitamin K is 90 mcg and 120 mcg for adult women and men, respectively.
Teenagers require only 75 mcg of vitamin K a day. Children require even lower dosages.
These doses are based on vitamin K intakes of healthy people. There haven’t been established recommended separate daily doses for vitamin K1 and K2. Many scientists believe it should.
Following a plant-based diet, rich in green leafy vegetables, is the easiest way to boost your daily intake of vitamin K1.
On the other hand, we get only a small amount of vitamin K2 from animal-based foods. Fortunately, good bacteria in the gut synthesize a modest amount of vitamin K2. Hence, the human body contributes to meet the daily requirements of vitamin K2.[2,3]
What’s the maximum dose of vitamin K I can safely take a day?
Actually, there hasn’t been established a maximum safe dose of vitamin K. Even extremely high dosages of vitamin K are rather unlikely to cause toxicity or any adverse effects in healthy people.
Furthermore, high doses of vitamin K are pretty safe because most of it isn’t absorbed. The body retains only 30-40% of vitamin K. The rest is rapidly metabolized and excreted.
Side effects of too much vitamin K
Healthy people can safely consume high doses of vitamin K, either from food or supplements.
On the other hand, people who are under medication should consult their physician before taking dietary supplements containing vitamin K, or drastically changing their eating habits.
Vitamin K may interact with a few medications.
For instance, heart patients who are taking blood thinners, such as warfarin (Coumadin®) should be very careful not to increase their vitamin K intake. Vitamin K can decrease the effect of warfarin, increasing the risk of blood clots! In this case, it’s vital to keep vitamin K intake consistent.
Do I need high dosages of vitamin K from supplements?
Vitamin K deficiency isn’t common. People who follow a well-balanced diet consume more vitamin K than the recommended daily intake.
It’s estimated that the average vitamin K intake from both food and supplements is about 160 mcg and 180 mcg for women and men, respectively.
Only people who follow a poor diet, low in vegetables, may consume low doses of vitamin K.
Moreover, certain drugs antagonize the activity of vitamin K and can lead to depletion of vitamin K. For instance, anticoagulants and antibiotics may have an adverse effect on vitamin K levels.
In fact, prolonged use of antibiotics can destroy vitamin K-producing bacteria in the gut, leading to low concentrations of vitamin K. In this case, vitamin K supplementation may be beneficial.
In contrast, people under anticoagulant medication need to maintain a consistent intake of vitamin K.
Furthermore, it can be difficult to get high doses of vitamin K2 from food. Especially, vegans and people who follow a plant-based diet don’t get any vitamin K2. Vitamin K2 is only present in animal-based foods.
In this case, taking a multivitamin containing vitamin K2 may be beneficial. As plants don’t contain either vitamin D, people who follow a plant-based diet might benefit from a vitamin containing both vitamin D and K2. You’ll find a wide variety of dietary supplements with both vitamin D3 and K2 at best prices on iHerb.
Do supplements exceed the maximum safe daily dosage?
First, you should prefer dietary supplements with vitamin K2. That’s the type of vitamin K that is hard to get from food.
Most dietary supplements contain vitamin K2 doses between 45-200 mcg, which is considered pretty safe.
Furthermore, according to studies, daily doses as high as 135 mg cause no adverse effects.
Always consult your healthcare provider before taking any dietary supplement, though.
Can I get too much vitamin K from food?
After all, Japanese consume natto (fermented soybeans) for hundreds of years with no adverse effects. Natto is the richest food in vitamin K2, containing more than 100 mcg of vitamin K2 per 100g! This may be a reason why Japan has a lower fracture risk and stronger bone density than other countries!
Moreover, many studies have been performed using extremely high vitamin K2 dosages of 45,000-90,000 mcg. No toxic effects or adverse effects have been reported.
It’s estimated that 90% of the total vitamin K intake from our diet is vitamin K1. But, only 10-15% of vitamin K1 is absorbed by the body.
Foods with vitamin K1
Green leafy vegetables are the richest foods in vitamin K1. Spinach, broccoli, lettuce, and even carrots are common foods rich in vitamin K1. Vegetable oils and some fruits contain moderate amounts as well. Fermented foods, such as natto, and cheese are also high in vitamin K1.
You could improve the absorption rate of vitamin K1 from vegetables by consuming them with a tbsp of any vegetable oil. Fat significantly improves absorption rates.
Foods high in vitamin K2
On the other hand, meat, dairy, fish, poultry, and eggs contain modest amounts of vitamin K2, but low levels of vitamin K1.
Health benefits of vitamin K
Vitamin K is a fat-soluble vitamin. It’s present in the liver and other body tissues, such as the brain, heart, pancreas, and bone.
Actually, Vitamin K is a family of compounds with a common chemical structure. There are two forms of this vitamin: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). We get vitamin K1 mainly from plant-based foods, while vitamin K2 is only found in certain animal-based, fermented foods and dietary supplements. Both types are vital for health.
Moreover, the human body produces small amounts of vitamin K2. Bacteria in the gut synthesize it.
Above all, vitamin K is important for our good health, as it’s necessary for the synthesis of proteins which clot the blood. A cut stops bleeding, partially due to vitamin K.
Also, vitamin K is involved in bone mineralization. It may help prevent fractures due to osteopenia and osteoporosis.
Some studies have linked vitamin K with higher bone mineral density, while other studies have found that vitamin K reduces the risk of fractures because it increases bone strength.
Both vitamin K1 and K2 protect from osteoporosis. According to studies, a vitamin K2 dosage of 45 mg could decrease the risk of hip fractures by 77%, while vitamin K1 dosages of 5 mg reduced clinical fractures by 50%.[6,7,8]
Hence, vitamin K2 is found in the supplements for preventing osteoporosis. Moreover, vitamin K2 isn’t present in many foods. Postmenopausal women could benefit from a supplement containing both vitamin K2 and vitamin D. Vitamin D also protects the bones!
Moreover, vitamin K may reduce the risk of coronary artery disease and all-cause mortality! Vascular calcification is a key risk factor for coronary heart disease. It reduces aortic and arterial elasticity. Vitamin K prevents vascular calcification.
Certainly, a diet rich in foods with vitamin K1 (green leafy vegetables) seems to suppress arterial calcifications and reduce the risk of cardiovascular events. But, getting high doses of both vitamin K1 and K2 is more effective for preventing and reversing arterial calcifications.
Furthermore, vitamin K seems to improve insulin sensitivity. Thus, it may prevent the development of diabetes and obesity. So, people who want to lose weight and people with diabetes should benefit from the regular consumption of green leafy vegetables.