When it comes to prostate cancer, the biggest challenge isn't detecting it. It's sorting the common tumors that won't harm you from the rare ones that can kill you.

Doctors haven't figured out the secret yet, but of course Mother Nature already has -- because there's one vitamin proven to stop the most dangerous tumors right in their tracks.

The good news is that it's a vitamin you can get easily for free. The bad news is, you're probably not getting nearly enough of it.

Yes, it's the same vitamin D you get from spending time under the sun… but don't get if, like most people, you spend the bulk of the day indoors (and cover yourself in sunscreen when you do head out to the beach).

That's a big mistake for everyone, because we all need our D. And it's an even bigger mistake for men, because the latest research from the Harvard School of Public Health finds that high D levels have a powerful effect on the worst-of-the-worst prostate tumors.

The study of more than 2,500 men tracked for nearly two decades finds that men with the highest blood levels of D were 57 percent less likely to die of those tumors than men with the lowest.

In fact, of the 114 men in the study who did die of prostate cancer, 31 were in the group with the lowest blood levels of D -- while just 19 came from the group with the highest.

The study didn't find any difference in the overall number of tumors, but I think the survival benefit alone means it's worth making sure you increase your D levels -- especially since studies have shown it's one of our biggest nutritional deficiencies.

The cheapest way, of course, is to head outside and soak up some rays. But the easiest way -- and the best way to make sure you consistently get what you need -- is by taking a supplement.

You don't have to be concerned about your prostate to boost your levels of this essential hormone (and yes -- despite the name, it's a hormone). You don't even have to be a man, because vitamin D is essential for everything from bone health to brain support -- and it can boost the immune system like nothing else out there.

But let's get back to prostate cancer, because along with vitamin D there's another all-natural substance that can help you beat the disease.

Keep reading!