(McClatchy-Tribune Information Services) -- Every winter, no one wants to get sick but few seem able to avoid it.

Start boosting your immune system this cold and flu season by thinking at the cellular level, said Dr. Rashmi Kaul, associate professor of immunology at OSU Center for Health Sciences.

Viruses and bacteria thrive in cold temperatures, and we lose the battle to protect our bodies against them by not staying hydrated enough, missing out on sleep, eating junk food and not getting enough exercise, among other bad habits.

"Most are very simple things we always ignore," he said.

Strengthen your body's immune system with Kaul's simple strategies:

1. Wash your hands.

Our first immunity defense is our skin, so washing those germy invaders off regularly -- warm water and good old-fashioned soap for at least 15 seconds -- helps us keep an important physical barrier against viruses and bacteria. Antibacterial soap isn't necessary, she said, and alcohol-based hand sanitizers can dehydrate your skin.

2. Drink lots of fluids.

The weather is cold and dry outside, the heater is cranked inside -- and we're not hydrating enough, usually.

Keeping your body well hydrated -- 8 to 12 cups of fluid a day -- helps the immune system work better, and flushes our systems of bacteria and viruses.

3. Go to bed.

"Sleep is very important

to conserve our energy," Kaul said. Energy your body needs to fight off viruses -- and keep your body from producing too much stress hormones. Stress is bad for the immune system, too.

4. Eat smart.

A diet rich in vitamin C and antioxidants helps protect your body's cells from harmful invaders -- cold and flu viruses, bacteria that cause sinus and bronchial infections. Eat oranges, broccoli, bell peppers -- fresh foods that are rich in vitamins and antioxidants. Fresh, because we absorb the vitamins and antioxidants better than in the synthetic forms (pills and supplements).

5. Get some exercise.

When we feel tired, run down or sniffly, sometimes the last thing we think about is hitting the gym or going for a walk or jog. But that's exactly what you should do, because the cardiovascular exercise will help blood flow and circulate throughout your tissue and help boost your immune system.

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