(MONEY Magazine) – Until recently, I knew more about the immune status of my aging SUV--due for an oil and filter change in 500 miles--than the immune status of my body. But I've changed my ways, and so should you. Cold and flu season isn't far off, and the time to start building your defenses is now. "In winter your immune system needs more protection, and this takes a few months to achieve," says Elson Haas, M.D., author of Staying Healthy with Nutrition. "So it's smart to start in September." By tuning up your bug-fighting abilities, you improve your chances of avoiding not just the misery of being sick but also the expense. Last year consumers spent more than $3.6 billion on over-the-counter remedies, in addition to money lost on co-payments, prescriptions and unpaid sick days. With a little forward thinking, many of those dollars could have been saved. And that's nothing to sneeze at.

Gauge Your Risk

If your immune system is vulnerable, you have a greater chance of getting a bug once exposed. And it takes you longer to shake being sick. How susceptible are you? Answer these questions to find out. • Did you have more than two bouts of cold or flu last year? • Do you suffer from allergies? • Do you often feel fatigued? • Do you get less than seven hours of sleep a night? • Do you notice that wounds take longer to heal than they should? The more yes answers you've given, the more aggressive you should be in trying to build up your defenses (see the next column for suggestions). If you said yes to four or more questions, head to your doctor for a pre-flu-season checkup, and ask whether you should have a complete blood count test, which shows how many disease-fighting white blood cells you have onboard. (Insurance usually covers this.) If your levels are too low, your physician can prescribe a course of action.

Get Your Guard Up

Stay cold- and flu-free with this 60-day Rx:

• CATCH UP ON Z'S A landmark Ohio State University study showing that students who pulled all-nighters had depressed immunity is one of several that link lack of sleep to greater susceptibility to illness. Adding as little as four hours of shut-eye a week may help, says Dr. Haas.

• EAT A YOGURT A DAY Lactobacillus acidophilus, a "friendly" bacterium, stymies the growth of bad germs. It's an ingredient in many yogurts; check the labels.

• GET VACCINATED The flu shot is up to 90% effective against common strains. If there's a shortage, high-risk groups such as kids and the elderly get first dibs. Others may still be able to get the shot at supermarkets or pharmacies--and yes, it's just as safe. Or ask your M.D. for the readily available nasal vaccine, FluMist.

• ADD SOME ASTRAGALUS Clinical trials suggest this ancient Chinese herb may prevent colds and help boost immunity. You'll find it at health food stores, but check in with your doctor before using it.

Mount a Swift Defense

If, despite your best efforts, you're struck with a cold or the flu, act fast to fight it.

• FOR COLDS (cough, runny nose, fatigue): Take a high-dose combo of vitamin C (1,000mg) and zinc (8mg), which have been shown to decrease the length of a cold when taken at the first signs of illness. Or consider taking echinacea. Some studies seem to show the herbal remedy as ineffective, but one recent clinical trial suggests that a high initial dosage (40mg/ml up to 48 hours after symptoms appear, followed by six days at 25.5mg/ml), taken from the right parts (root and flower) and species (purpurea), can markedly reduce symptoms.

• FOR THE FLU (fever, fatigue, achiness, chills): Up to two days after symptoms begin, ask your doctor for a prescription for Tamiflu or Relenza. These relatively new antiviral drugs have been found to be effective in shortening the course of the flu by a day or more. Last year there was a shortage, but ample supplies are expected for the upcoming flu season.

Curtis Pesmen is the author of The Colon Cancer Survivors' Guide.

$3.6 billion

How much U.S. consumers spent on over-the-counter cold, cough and flu remedies in 2005

SOURCE: ACNielsen.