Anyone who's battled depression knows it can be like living inside a bad dream. But seniors should have some extra motivation to keep a positive outlook on life--because the latest studies show that any battle with the blues can turn into aging's ultimate nightmare: dementia.

Depression can increase your risk for Alzheimer's disease by up to 50 percent, and multiple episodes can double that already high risk.

In the first of three new studies published in Neurology, researchers looked at the data on 947 patients with an average age of 79 who took part in the Framingham Heart Study. None of the patients had any signs of dementia at the start of the study, but 13 percent of them--125 patients--were depressed.

During the 17-year study period, 136 patients eventually suffered from Alzheimer's disease, and 28 others were diagnosed with other forms of dementia. That might not sound like a lot, but here's the kicker: The depressed patients were 50 percent more likely to be among the people who developed dementia.

And because those depression battles took place so many years earlier, the researchers believe the condition is a true risk factor for Alzheimer's--and not simply a symptom of the disease.

In the second new study, researchers looked at data on 350 Chicago dementia patients over a 10-year period--seven years before the dementia diagnosis, and three years afterwards.

During that time, the depression symptoms barely changed, even as the disease took hold. The researchers say that's more proof depression is independent from Alzheimer's, and not a sign of it.

And in the third new study, researchers found that two or more depression battles in your later years can double your risk of dementia.

Researchers aren't quite sure how depression leads to dementia--but one of the leading theories is that it can actually damage the brain, creating the conditions that allow dementia to take hold later.

Naturally, Big Pharma would love to see new dementia fears lead millions of seniors down the path toward antidepressants.

But drugs aren't the only way to change your blues to another color--they're not even the best way. Research has consistently found that everything from talk therapy to exercise to herbal treatments such as St. John's wort can all work far more effectively than common meds--and with far less risk.

The key is taking the time to find the safe solution that's effective for you.