Even if you take precautionary measures this winter, such as getting a flu shot and washing your hands frequently, there is still one more "X" factor to consider: a strong immune system. Your immune system is your body's watchdog, and it's always looking out for you. First, it manufactures antibodies, which identify and fend off invaders. Also, your immune system has a built-in memory: It remembers how it defended your body against those past invaders, and it stands ready to do it again. This is actually how vaccines work.

Here are five ways to give your hardworking immune system a boost during the season of sniffles.

1. Get enough sleep.

Just like the rest of you, your immune system gets weary, and too little sleep compromises its ability to protect you against sickness. Aim to get at least seven to eight hours of sleep a night.

2. De-stress.

Chronic stress causes your body to be in a constant "fight or flight" mode; in fact, stress causes your body to secrete certain substances that weaken your immune system. Taking steps to reduce stress in your life—whether that means taking yoga classes, getting regular massages, or saying "no" more often when you're spread too thin—will help your immune system stay in top shape.

3. Eat right.

There is a definite correlation between overall health and strong immunity, and what you eat plays a big role. Experts recommend loading up on vitamin B6 and B12, and eating a diet low in red meat and high in fruits, vegetables, and fish. There also is evidence that chicken soup can help strengthen your immune system—all the more reason to cook up a fresh batch right now!

4. Exercise more.

When it comes to exercise and immunity, it's important to find the right balance. Exercising too much or exercising when you're already starting to feel sick can actually weaken your system. But moderate exercise such as brisk walking, jogging, or bicycling three to four times a week is a great way to keep your immune system going strong.

5. Enjoy yourself.

Preliminary research suggests that listening to your favorite music is one way to help your body make more IgA, a protein that helps fight infections. And the birds and bees just might have something to say on this matter, too: Being intimate is another way to give your immune system a boost of IgA. Whatever activity you choose, make sure it is both relaxing and enjoyable. In the words of an often quoted pop song: Don't worry; be happy.