The other big cause of cancer

Everyone knows smoking is the single biggest cancer risk factor. But most people can't name number two on the list, despite the fact that this cancer cause is far more common than cigarettes.

It's obesity -- and a new report out of the UK blames it for 17,000 cases of cancer each year in that country alone.

That's a lot of cancer... but that's small potatoes compared to the numbers here in the United States, where obesity is responsible for nearly 100,000 new cases of cancer every single year.

And while smoking has been linked to at least 14 types of cancer, obesity is no slouch in this department either: Excess weight is a major risk factor for cancers of the esophagus, pancreas, colon, rectum, breast (especially after menopause), kidney, thyroid, and gallbladder.

It's also a risk factor for endometrial cancer, which is cancer in the lining of the uterus.

Obesity leads to excess insulin and insulin growth factor-1, which is why people who gain weight are at risk for diabetes. But excess insulin and IGF-1 can also promote or even cause cancer.

Fat cells can also produce hormones that stimulate the growth of other cells -- including tumor cells.

And of course obesity can stimulate the production of estrogen, and excess estrogen can lead to certain types of breast cancer.

Once you have the disease, obesity can even make it harder to treat -- especially those breast cancers, since the drugs for the condition work by attempting to block the estrogen that's feeding the tumor.

If your estrogen levels are higher in the first place thanks to excess weight, those drugs have a hard time keeping up. One new study finds that obese breast cancer patients have double the levels of estrogen of normal-weight patients after taking those meds.

Not every cancer risk factor is within your control, with plenty of cases caused by some combination of bad genes and worse luck. But the new numbers out of the U.K. find that smoking, obesity, and other lifestyle factors are responsible for up to 40 percent of all cancers.

That means 40 percent of all cancers never had to happen.

We've done a great job educating the public about the dangers of smoking, to the point where even people who haven't quit at least know they should.

Now, it's time to do the same for obesity.

Speaking of cancer, I've got an update on a possible cause many people don't know about... yet.

Keep reading!