"It's really pretty simple," says Connie Diekman, RD, director of University Nutrition and immediate past president of the American Dietetic Association. "There are three key things to think about. Number one is hydration. Number two is foods and Number three is lifestyle issues."

Hydration is essential all the time of course, Diekman says, but when it's very cold or very hot we lose more fluid and can get dehydrated more quickly.

"This time of year you need to keep your fluids up," she says. "If you are sick or if you want to prevent the flu, that hydration is important to make sure your lungs stay clear and don't get congested."

Diekman says that dehydration can also lead to lightheadedness, poor concentration and compromised performance overall.

"To keep your immune system healthy you want to focus on protein, Vitamin C, zinc and iron," she says. "Those are really the four big players that keep your immune system up. Meat, fish, poultry, beans, nuts and seeds. All of that, but then the Vitamin C piece of course is fruits and vegetables. If you can do that, you're giving your immune system what it needs."

The last variable is lifestyle. The most important, says Diekman, is adequate sleep followed by adequate physical activity. It's also good to keep your hands clean and keep them away from your face.

"If it's finals, adequate may be very different than if it's the middle of the semester," she says. "The exercise can be walking. It doesn't have to be the gym. Just get out and take a walk."

Obviously there are no guarantees you can prevent a virus, Diekman says, but if your immune system is strong you'll have a better chance of not catching something and if you do, you'll be able to fight it better.

Provided by Washington University in St. Louis (news : web)