Why it's not true: If you think you lose brain cells as you get older, and those cells are gone forever, think again. Research shows that some areas of the brain involved with memory and learning continue to produce new nerve cells every day. So while you do lose brain cells every day, you also are constantly replacing brain cells.
The best thing you can do to build new brain cells is to keep your brain active with new activities and learning. And one of the best things you can do for your brain later in life, research shows, is learn a new language. (Though learning anything new is good for your brain.)
One more thing about your brain: Only 3 to 4 percent of disease-related gene mutations, including mutations for Alzheimer's disease, are genetically determined. Most disease-related gene mutations are influenced by lifestyle — including emotions, quality of sleep, diet and stress levels. You don't have to get Alzheimer's disease or lose mental alertness as you grow old, unless you have a rare gene mutation.