Sign of Dementia (a disabling form of memory loss, such as Alzheimer's): You get lost for hours walking or driving in familiar territory

Sign of Normal Aging: You are more concerned than family members about your episodes of forgetfulness

Sign of Dementia: Family members are more concerned than you about your incidents of memory loss

Don't assume it's Alzheimer's if you walk upstairs, only to say to yourself, "What did I want up here?" It could be that you're simply trying to remember too many details at once or that you're tired, sick or just plain distracted.

The normal loss of brain cells between the ages 30 and 70, coupled with the expected 15 to 20 percent decline in the brain's blood flow among neurons, could account for any slight slide in memory, learning and intelligence.

But you can take some steps to preserve your memory, according to Harvard cognition experts, who recommend that you:

1. Exercise. Physical fitness often goes along with mental fitness.

2. Continue to learn. Taking adult education classes, reading regularly, taking up a new hobby or playing Scrabble or another challenging game can keep your mind strong.

3. Don't smoke. Studies show that smokers forget people's names and faces faster than nonsmokers.

4. Eat a healthful diet. Maintaining a normal weight and eating antioxidants can help you avoid memory-impairing illnesses.

5. Get enough sleep. Strive for eight hours to allow your brain to consolidate the day's lessons.

6. Consider taking vitamins such as C and E. They might protect against some forms of dementia, though they probably won't protect against normal, age-related memory loss.

7. Consider taking estrogen if you're a woman going through menopause. Drops in estrogen may contribute to memory loss so consider, with your doctor, whether hormone replacement therapy is right for you.

8. Maintain social connections. Close ties with others seem to improve older people's mental performance.