The Damage: Prolonged exposure to the fight-or-flight hormone cortisol and other brain chemicals can actually kill neurons by exciting them to death.
The Fix: Stay connected. A six-year Harvard University study of 16,638 people found that those with the largest social networks had the slowest rate of memory decline. Family and friends can mute the intensity of stress—and the brain's chemical response.
9. Thief: Cholesterol
The Damage: If plaque gets lodged inside one of the tiny blood vessels in your brain, it can cause a "silent" stroke (the kind you don't even know you've had). The harm this can do to your brain tissue could slow the speed at which you absorb new information.
The Fix: In addition to eating a healthy diet and getting plenty of exercise, go nuts for nuts. Eating about 2.4 ounces a day can lower bad cholesterol by ten points. The type of nut doesn't seem to matter, though raw nuts are healthiest.
10. Thief: Sleep Apnea
The Damage: In this disorder (marked by loud snoring and exhaustion upon waking), your airway spontaneously closes or becomes blocked for several seconds at a time. The result—a dip in the oxygen level in your blood, which can cause brain cells to starve.
The Fix: Studies show that losing 10 percent of your body weight is enough to improve symptoms. And your doctor may recommend using a CPAP (continuous positive airway pressure) machine while you sleep. It fits over your nose and mouth and generates a steady flow of air to keep the airway open.
11. Thief: Hypothyroidism
The Damage: An underactive thyroid slows metabolism, which leads to fatigue, which leads to a foggy brain. One of the symptoms of this disorder, affecting about 17 percent of women 60 and over, is difficulty committing new info to long-term memory.
The Fix: A common cause of the problem is insufficient levels of iodine, which the body needs in order to produce thyroid hormones, so seek out lots of iodine-rich foods, such as seafood and dairy products.
This article is part of Oprah.com's 2011 Feel Good Challenge. Join now—and move closer to the life you want!