Top Ten Immune Busters...Courtesy of Prevention

These 10 habits can make your immune system shut down, so follow this advice and your body will thank you.

1. Junk the Junk Food

Combined with sedentary lives, a poor diet is estimated to kill between 310,000 and 580,000 Americans each year.

So, how bad is junk food for your immune system?

Experts have known for some time that when a person is malnourished, her immune system is weakened. When you restore the person to normal nutrition, her immune system improves, which is no surprise. But what they're just learning is that when you continue to improve nutrition beyond mere adequacy, the immune system continues to improve, even in healthy people.

One thing that a lot of junk food has in common is excess fat. Fats, especially polyunsaturated fats, tend to suppress the immune system. Cut your total fat intake to no more than 25% of daily calories.

Another bad component of junk food is excess sugar. Sugar inhibits phagocytosis, the process by which viruses and bacteria are engulfed and then literally chewed up by white blood cells.

2. Dodge Those PCBs

It takes just one exposure of less than one-millionth of a gram for immunotoxic contaminants such as polychlorinated biphenyls (PCBs), mercury, certain pesticides, and dioxin-like substances to disrupt the immune function of innocent wildlife. Since these chemicals can stay in the environment for decades, vulnerable wildlife species have no escape from their devastation. Moreover, not only do these toxins become more concentrated as they move their way up the food chain, they can also cause life-threatening autoimmune reactions--the immune system's inability to tell the difference between the body's own tissues and foreign invaders.

So, what does this have to do with your immune system? A lot. Evidence suggests that some of these same chemicals may be putting us at risk. A few examples: In Aberdeen, N.C.--home of the Aberdeen pesticides dump--scientists found that young adults were two times more likely than nonresidents to have shingles, a painful condition caused by a herpes virus. In another study, researchers found that chlordane, a termite-killing substance, caused weaker immune responses in people who had been exposed.

So what can you do? Reduce your exposure as much as possible to unnecessary toxins. Stay away from cigarette smoke, excess alcohol, and illicit drugs. Buy organic produce when possible. Rinse your fruits and vegetables thoroughly to remove pesticides. Switch to natural gardening methods and stay indoors or go away when your neighbors are using pesticides. Choose cleansers, paper goods, and other products that are made with less toxic materials. Read food labels vigilantly and avoid products that contain unnecessary chemicals.

3. Avoid Sleep Deprivation

Sleep deprivation has a powerfully detrimental effect on your immune system. The perfect example is college students who get sick after pulling all-nighters cramming for exams.

If you're tired when you wake up in the morning, you're not getting enough sleep, or maybe not enough quality sleep. Either way, your immunity is probably compromised. Poor sleep is associated with lower immune system function and reduced numbers of killer cells that fight germs. Killer cells are also the part of the immune system that combats cells that divide too rapidly, as they do in cancer. Lower their numbers and you may be at greater risk for illness.

Studies have shown that chronic sleep deprivation also contributes to heart disease, gastrointestinal problems, and other medical illnesses. One study on the effects of sleep deprivation showed that a group of men restricted to 4 to 6 hours of sleep per night experienced changes in hormone function and carbohydrate metabolism that mimic aging changes; the lack of sleep was making them older faster.