High in prebiotic carbohydrates called fructans, asparagus delivers plenty of potassium, vitamin A, vitamin K and anti-inflammatory phytochemicals.LARRY CROWE/The Associated Press
The health benefits of consuming enough vitamins C and D, calcium and iron are well-known. These nutrients support our immune system, build and maintain strong bones and, in the case of iron, allow our cells to produce energy.
You might not give much thought, however, to vitamin K. But you should.
Growing evidence suggests this lesser-known nutrient plays an important role in healthy aging. Here’s what to know.
Vitamin K basics
This fat-soluble vitamin occurs in two forms. Our main dietary source comes from a compound called phylloquinone, or vitamin K1. It’s plentiful in green leafy vegetables, like spinach and kale, and some vegetable oils.
The other type, vitamin K2, is a family of compounds called menaquinones. You’ll find K2 in meat, dairy, eggs and fermented foods including cheese and natto (fermented soybeans).
Vitamin K’s most famous role is helping our blood clot normally. Scientists are learning, though, that the nutrient has important roles beyond blood clotting.
Vitamin K and bone health
Studies suggest that consuming too little vitamin K may harm your bones as you age. That’s because vitamin K activates important proteins in the body that build and strengthen bones.
Large observational studies have tied higher vitamin K1 intakes to a significantly lower risk of hip fracture. In one study conducted in more than 800 elderly men and women, participants whose daily diets contained the most vitamin K1 (254 mcg) compared to the least (56 mcg ) had a 65 per cent lower risk of hip fracture.
Research from Japan, where vitamin K2-rich natto is a traditional dish, found that postmenopausal women who consumed natto every day, versus not at all, had a significantly slower rate of bone loss over three years.
Vitamin K and heart health
A number of studies have tied a higher vitamin K intake and higher vitamin K blood levels to a lower risk of cardiovascular disease.
A recent Danish study, published in August, found that among 53,000 adults who were followed for 23 years, those who consumed the most vitamin K1 (192 mcg per day) – versus the least (57 mcg) – were 21 per cent less likely to be hospitalized for cardiovascular disease related to atherosclerosis (such as plaque build-up in the arteries). Higher intakes of vitamin K2 were also protective.
Vitamin K activates a specific protein that inhibits vascular calcification, a risk factor for heart disease and stroke. Vascular calcifications are calcium deposits on the walls of blood vessels that cause narrowing and reduced blood flow. Vitamin K may also reduce inflammation in the body.
How much, which foods?
The adequate intake (AI) for vitamin K, established in 2001, is based on the amount consumed by healthy people. The daily AI for vitamin K is 90 mcg for women and 120 mcg for men. It’s unknown whether this amount is optimal for bone or heart health.
The best sources of vitamin K1 are green leafy vegetables. For every one half-cup cooked, you’ll find 445 mcg in spinach, 286 mcg in Swiss chard, 386 mcg in collard greens, 246 mcg in kale and 110 mcg in broccoli.
For every one cup raw, kale delivers 472 mcg of K1, spinach has 145 mcg and romaine lettuce provides 45 mcg. If you like tabbouleh, one quarter-cup of chopped parsley contains 246 mcg. A tablespoon of olive and canola oil each provide 10 and 8 mcg of K1, respectively.
Natto is an excellent source of vitamin K2, supplying 850 mcg for every three-ounce serving. Small amounts of K2 are in cheese, eggs, liver, meat, poultry and fish.
You’ll improve absorption of vitamin K by including a source of fat in your meal such as oil, avocado, nuts or seeds.
If you take warfarin, a prescription anticoagulant used to prevent blood clots, it’s necessary to eat a consistent amount of vitamin K each day. Any big changes in vitamin K intake can interfere with warfarin’s ability to thin the blood.
Do you need to supplement?
Vitamin K is available in multivitamins, bone health supplements and single vitamin K1 or K2 supplements.
There’s limited and weak evidence that vitamin K1 or K2 supplements benefit bone health. While emerging data from small trials on supplementation and heart health is promising, at this time there isn’t strong evidence to support the need to take a separate vitamin K supplement.
To get your vitamin K, eat leafy greens every day. A multivitamin can also support your diet.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD
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