It's so easy it seems unreal: A key weapon in the fight against diabetes might be hovering right outside your window, right now.

It's the sun -- the primary source of vitamin D, and a new study shows how this pancreas-boosting super nutrient can
help stop the disease before it starts.

Researchers gave 92 pre-diabetics either vitamin D3 supplements, calcium supplements, both, or a placebo for four months -- then ran some blood tests and found that patients who took the D3 had slightly better blood sugar levels.

Not that big of a deal.

But this is a big deal: The patients who took D3 had dramatically better pancreas function -- with the organ's beta cells showing improvements of up to 30 percent.

Those beta cells are needed to make insulin -- and when they stop doing their job, you get diabetes.

The researchers wrote in the American Journal of Clinical Nutrition that calcium didn't make a difference when it came to giving those cells a lift -- just the D3.

It's not the first study to make the link: Research has found time and again that vitamin D can help control blood sugar levels (even more so than in this study) and lower the overall risk of diabetes.

One study last year found that people middle aged and older with the highest D levels had a 55 percent lower risk of type 2 diabetes and 51 percent lower risk of metabolic syndrome than those with the least.

That should be enough to entice any pre-diabetic into spending more quality time under the sun, or at least investing in a quality D3 supplement -- but while the sunshine vitamin is a great place to start, you'll need a few more weapons if you hope to win the war against this disease.

Cinnamon -- as in the spice, but you'll want the extract -- has shown an amazing ability to slash blood sugar levels and reduce your blood pressure, while the mineral chromium can reduce both fasting insulin and fasting glucose levels.

And if you want to put some punch into your plan, try Popeye's favorite source of power: spinach. This leafy green is packed with magnesium, which studies have shown can lower your levels of insulin resistance and slash your risk of diabetes. (Read more here.)

Your body also needs magnesium to put its vitamin D to work -- so if you're going to get one, be sure to get the other.

Up next: More on vitamin D.