This week, I want to talk about one of the world's least understood vitamins: vitamin K. Discovered in 1929 by a Danish scientist, this vitamin plays a role in helping your blood to clot.

But try to use the three words "vitamin" + "blood" + "clot" together in a sentence and it's like screaming the word "FIRE" in a crowded movie theater. It sets off panic, especially for anyone worried about having a stroke or heart attack. No one wants to take a vitamin known for helping your blood to clot. For this reason, most manufacturers omit it from their multivitamins (except the most high-end formulas).

Nevertheless, vitamin K is essential to good health. It may even protect you against cancer. In fact, a new study has found that this once-blacklisted vitamin may decrease your risk of lung and prostate cancer by up to 60 percent.

The many uses of vitamin K

Vitamin K is a fat-soluble vitamin that helps our blood to clot. To be more precise, it helps your body clot exactly the right amount. And, yes, you do need your blood to clot in certain instances, like when you get a cut or following surgery.

On the other hand, no one wants his or her blood to clot too easily, as that could put you at risk for a stroke or heart attack. To prevent blood clots, some people are prescribed aspirin or blood-thinning drugs like Coumadin. These drugs prevent clots by destroying any vitamin K stored in your body. But taking these drugs often sets the stage for the opposite problem: blood that doesn't clot ENOUGH. And when this happens (and it actually happens fairly often) doctors try to add vitamin K back into your system.

Additionally, recent research has found that vitamin K is important to bone health. Naturopath docs also use vitamin K to fight tooth decay, varicose veins, and menstrual problems (especially when blood clots are involved).

Most recently, vitamin K has been found to have a role in stimulating the immune system (though probably not as much as D). I suspect that this is how scientists, in the most recent study, stumbled upon the connection between vitamin K and cancer.

New cancer research on vitamin K...

In recent lab tests, vitamin K has already been shown to block cancer cell growth. The vitamin does this by setting off a chemical reaction called "apoptosis." So instead of multiplying wildly -- as cancer cells normally would do -- the cells exposed to vitamin K die off.

With that lab research in mind, German scientists wanted to see if people with high vitamin K intake would have some added protection against cancer.

They enrolled nearly 25,000 healthy men and women ages 35 to 64 and asked them to complete dietary questionnaires. Then, they analyzed the food diaries to gauge the participants' intake of vitamin K.

Over the next decade, 1,755 of the men and women from the study got cancer. But when the team examined which participants got cancer, they found a powerful connection to vitamin K.

In fact, men and women with the highest intake of vitamin K2 (a form of vitamin K) developed 50 percent fewer cases of lung cancer (compared to those with the lowest intake). Plus, men with the highest intake of K2 developed nearly 60 percent fewer cases of prostate cancer (compared to men with low K2).

A little bit goes a long way

There are two natural forms of vitamin K. The first -- K1 -- is found in green leafy vegetables, like spinach. The second -- K2 -- is found in meat, cheese, and natto (Japanese fermented soybeans). But if you follow a vegan or carb- heavy diet, it's very easy to become deficient in K2. And that's unfortunate. Because -- as you'll recall -- K2 is what the German scientists found protected the men and women from cancer.

But you don't need a ton of it. In fact, the men and women from the study with the most vitamin K in their diets actually came in slightly under the recommended daily intake (120 mcg for men and 90 mcg for women). So this just goes to show, you don't need mega-doses of the vitamin to reap the benefits.

In most cases, I don't recommend taking a separate vitamin K supplement. Sometimes you'll find a dusting of K2 in the highest quality anti-aging nutritional formulas. When you take this kind of mega multivitamin, it's actually quite safe and beneficial to get a little extra K2. That is, unless you're prone to blood clots. So make sure to check with your doctor if that's a concern.

For most people, I recommend focusing on eating K-rich foods. You'll get plenty of K1 by eating green leafy vegetables, like spinach and kale. You'll get K2 by eating fermented cheese (like feta), butter, sauerkraut, organ meats, and egg yolks. Just remember, always eat eggs poached, over-easy, or hard-boiled to leave the yolk intact. This way, the yolks will actually retain all their nutritional value.