It's ironic that from 1968-78 Peter Falk's character "Columbo" was best known for looking befuddled and forgetful and then suddenly recalling, "just one more thing." Those well-scripted memory lapses predated a real-life battle with Alzheimer's disease that Falk would fight some 29 years later.

That kind of forgetfulness is what researchers from UCLA's Longevity Center spotted in many of the 18,000 folks ages 18 to 99 they interviewed recently. When the participants were asked if they believed that their thinking ability had declined in the past decade, 14 percent of younger adults, 22 percent of middle-aged and 26 percent of seniors said yes. That self-evaluated assessment of what's called subjective cognitive impairment, or SCI, is a reliable indicator of possible future cognitive problems. Researchers asked about lifestyle habits, too. What they found: SCI is associated with depression, lack of physical activity, high blood pressure, diabetes, obesity, smoking and lack of education.

Other research shows that 55 percent of folks with SCI develop clinically recognized mild cognitive impairment within seven years. (Only 15 percent of people without SCI progress to MCI after that length of time.) Once MCI develops, it can take about 15 years for mild dementia to set in.

Fortunately, SCI isn't an inevitable precursor to dementia; you can do a lot to protect your brain if you avoid smoke (from cannabis and tobacco), seek treatment for depression, control blood pressure and weight, avoid diabetes, stay physically active and manage stress. Oh, and just one more thing: Keep your mind active by constantly learning new things.