Your immune system plays a vital role in protecting your body against infectious organisms and cancerous cells. Though you cannot see it, your defensive team stands ready to confront germs and foreign invaders whenever they attack.

Most of the time, this works out well. Just think of a fever that went away or, perhaps, a recent cold that resolved seemingly on its own.

But a number of factors can gradually break down your barrier against illness. This quiz covers top threats to a healthy immunity and ways to defend against them. See how you do.

1. Which is not part of a healthy immune system?

a. Tonsils

b. Lymph nodes

c. Adam’s apple

d. Spleen

2. Your immune system gets stronger with age. True or false?

3. Poor nutrition can weaken immunity. True or False?

4. Which substance poses the largest threat to your immunity?

a. Tobacco smoke

b. Air pollutants

c. Moderate amounts of alcohol

d. Appropriately prescribed antibiotics

5. What relaxation technique(s) strengthen the immune system?

a. Yoga

b. Deep breathing

c. Meditation

d. All the above

6. People who exercise have healthier immune systems. True or False?

7. Immunity is better when you’re overweight. True or False?

Answers

1. c. Your immune system consists of white blood cells and your bone marrow, spleen, thymus, tonsils, adenoids and lymph nodes. Special assignments go to your white blood cells as they circulate through your body to scout out and destroy foreign invaders. The Adam’s apple, the bony protuberance in your neck that forms the front part of the voice box, is not a component of your immune system.

2. False. The function of the immune system typically declines with age. After about 50 or so, your immune system gradually grows slower and less ready to react. Inflammation, which tends to accumulate with age—often manifesting as heart disease, diabetes or other chronic ailments—may also weaken your immune system.

3. True. Plant foods contain vitamins, minerals and other substances that help maintain a healthy immune system. I recommend eating a balanced diet rich in fruits, vegetables, legumes and whole grains. The beneficial bacteria found in yogurt may also help boost immunity.

4. a. Quitting smoking is essential for better immunity. It’s also important to minimize your exposure to fumes and other pollutants, drink alcohol only in moderation, and take antibiotics and drugs only when truly necessary.

5. d. When you’re under stress, your body produces the stress-hormone cortisol. This hormone promotes wound healing but inhibits the ability of your immune system to keep diseases in check.

Luckily, stress-reduction techniques like yoga, deep breathing, meditation, and relaxation exercises may help reduce cortisol levels. Keeping levels low with regular relaxation can improve your immunity.

6. True. Physical activity builds your body’s defenses in several ways. It increases circulation of your body fluids and blood cells. Exercise also reduces immunity-destroying inflammation.

7. False. Hormones made by fat cells promote inflammation. The greater the inflammation, the greater your susceptibility to infection and disease. To reverse the inflammatory process, try losing a little weight. A loss of as little as 5 to 10 pounds can make a difference.

For more information: Centers for Disease Control and Prevention, www.cdc.gov.