Vitamin D is vitamin D--and all forms of the sunshine vitamin are created equal, right?

Not so fast.

In reality, D supplements can be as different as night and day--and if you're taking the wrong stuff, your body could be missing out big.

A new study shines a light on the difference between Ds, but before I get into the details I want you to go get your own supplement.

It's time for a label check.

Somewhere on the bottle--often right on the front--it'll tell you if your vitamin contains D2 (ergocalciferol) or D3 (cholecalciferol).

The one you want is D3.

If it says D2, don't worry and don't panic--it's not dangerous and it won't hurt you.

But it might not help you, either, because the study confirms that D2 just isn't absorbed by the body very well--and that means you'll want to replace it with a quality D3 supplement as soon as you can.

Researchers randomly assigned 33 adults with an average age of 49 to receive 50,000 IU a week of either D2 or D3 for 12 weeks, then tested their levels of 25- hydroxyvitamin D, also known as 25(OH)D.

Don't worry, this isn't a chemistry test--all you need to know here is that even the mainstream considers 25(OH)D to be the most reliable indicator of overall D levels, since it's the form that stays in you the longest.

In fact, it has a half-life inside your body of up to 15 days.

And as the researchers wrote in the Journal of Clinical Endocrinology & Metabolism, D3 is up to 87 percent more potent at raising serum levels of 25(OH)D, and three times more effective at raising fat calciferol levels, than D2.

The researchers say they'd like to see a longer-term study of the differences between D2 and D3--but you don't need to wait for the outcome of that, since other studies have also found that D3 is far more effective than D2.

Even the National Institutes of Health has acknowledged that D2 is less potent at higher levels--in other words, the levels you'll get from a supplement.

And since vitamin D has quietly turned into one of our most glaring nutritional deficiencies, you almost certainly need that supplement.

Make sure you get it--studies have shown that D can help lower the risk of dementia, heart disease, cancer, and may even lead to longer lives.