Animal studies indicate that chronic stress actually shrinks the memory centers of the brain and shortens life expectancy. And if you inject a human volunteer with the stress-response hormone cortisol, it causes temporary memory impairment.

Exactly how chronic stress shortens life expectancy is not clear, but some studies have suggested that it compromises the immune system, thus lowering the ability to fight off infections.

Chronic stress also impacts the digestive system, and can increase the risk for ulcers and irritable bowel syndrome.

In addition, stress elevates blood sugar levels, which can increase the risk for diabetes. Chronic stress also increases body weight and obesity rates by stimulating the appetite hormone leptin as well as the mood-altering chemical serotonin.

A 20-year study of about 13,000 volunteers showed that chronic stress elevated the risk of death from stroke or heart disease.

The good news is that you can reduce the negative impact of stress through meditation, yoga, tai chi, and other relaxation methods, which improves mood and boosts memory abilities. Meditation even rewires the brain and lengthens the telomeres of chromosomes, which has been shown to lead to longer life expectancy.

Spending time with friends and getting a good night’s sleep are other important strategies to reduce stress.

Keep in mind that it’s a great idea to combine some of these strategies in what I call the “triple threat” against Alzheimer’s disease: take a walk with a friend. The physical exercise will boost your brain health.

The conversation will stimulate your brain cells, and if you can talk about what’s worrying you, it will reduce your stress levels.