There's a good chance you're deficient in it and you probably don't even know it. In fact, it's estimated that at least 50 percent of the U.S. and U.K populations are deficient in vitamin D, and depression risk rises with deficiency, to make matters worse. (One major study estimates that U.S. deficiencies run as high as 75 percent!)

Then, to add insult to injury, if you've managed to somehow avoid it up until now, as your age rises your chance of acquiring a deficiency goes right up with it. Research has found that a staggering 88 percent of seniors may be below optimal levels.

Oh, and if you're a menopausal woman, well, the chances of you falling short of getting the recommended daily amount of it is nearly 100 percent.

I'm talking about vitamin D.

And running low on this vital vitamin is nothing to sneeze at. In fact, the major diseases that deficiencies of vitamin D have been linked to run the gamut and include atherosclerosis, cancer, osteoporosis, obesity, Alzheimer's, cognitive decline, multiple sclerosis, Parkinson's, diabetes, and even depression.

Researchers connect the dots to reveal link

Now the vitamin D and depression link may not come as too much of a surprise to you since it was only a couple of months ago that I told you that vitamin D was linked to less depression in women. Research conducted by Harvard scientists had shown that women with higher levels of vitamin D3 (the active form of the vitamin in the body) have a lower risk of depression.

But, as is so often the case with natural protocols, the finding regarding vitamin D and depression created its share of controversy and when a couple of smaller studies failed to back up the Harvard study the naysayers' tongues started wagging.

However, a new large-scale study, published in the journal Mayo Clinical Proceedings, has put a swift end to the controversy. That study—conducted at UT Southwestern Medical Center—examined the records of nearly 12,600 volunteers and definitively confirmed a relationship between the vitamin and mental health.

Patients with the highest levels of vitamin D were found to have significantly fewer incidents of current depression. The link was even stronger when they looked at the volunteers who had a prior history of depression.

A drug free way to drive away depression? Sign me up!

Down in the dumps? Check your D

Now of course the UT Southwestern team stopped just short of saying that low vitamin D levels may lead to depression. Instead they only admitted that there's a strong connection between vitamin D and depression. And, in fact, despite evidence of widespread deficiencies they didn't even recommend supplementing with vitamin D.

But while the researchers appear to be stalled at the crossroads of the chicken or the egg highway, I have no intention of getting stuck there with them. Or of leaving you stranded there, either.

While I certainly can't argue that more research needs to be done on the exact relationship between vitamin D and depression with so many of us already deficient in the nutrient I still heartily recommend that you work on shoring up your own levels.

And here's how...

As I'm sure you already know, your body naturally converts sunshine into good old vitamin D. So my first suggestion is as simple as they come...spend more time outdoors. I usually recommend 20 to 30 minutes a day without sunscreen in the morning sun if you can fit it in.

You can also increase the amount of vitamin D you get in your diet. In fact, remember that Harvard study I mentioned earlier? The researchers on that study found that women who ate foods containing at least 400 IU of vitamin D3 per day reduced their depression risk by about 20 percent. Try eating more tuna, salmon, halibut, sardines, and eggs.

And finally you can try a vitamin D supplement. You can safely take up to 5,000 IU of vitamin D3...the form of vitamin D most readily absorbed by the body...a day.

Let's just hope that while you and I are feeling on top of the world our buddies over at UT Southwestern don't end up too D deficient and down in the dumps to continue their research.