1. You're short on sleep.

You may have noticed you’re more likely to catch a cold or other infection when you’re not getting enough sleep. A lab experiment bears this out: When students at the University of Chicago were limited to only 4 hours of sleep a night for 6 nights and then given a flu vaccine, their immune systems made only half the normal number of antibodies.Not getting enough sleep can lead to higher levels of a stress hormone. It may also lead to more inflammation in your body.Although researchers aren’t exactly sure how sleep boosts the immune system, it’s clear that getting enough – usually 7 to 9 hours for an adult – is key for good health

.2. You don't exercise.

Try to get regular, moderate exercise, like a daily 30-minute walk. It can help your immune system fight infection.If you don't exercise, you're more likely to get colds, for example, than someone who exercises. Exercise can also boost your body's feel-good chemicals and help you sleep better. Both of those are good for your immune system

.3. Your diet is off.

Eating or drinking too much sugar curbs immune system cells that attack bacteria. This effect lasts for at least a few hours after downing a couple of sugary drinks.Eat more fruits and vegetables, which are rich in nutrients like vitamins C and E, plus beta-carotene and zinc. Go for a wide variety of brightly colored fruits and vegetables, including berries, citrus fruits, kiwi, apples, red grapes, kale, onions, spinach, sweet potatoes, and carrots.Other foods particularly good for your immune system include fresh garlic, which may help fight viruses and bacteria, and old-fashioned chicken soup. If you do come down with a cold or the flu, a bowl of chicken soup can help you get well faster, one study shows.
COPIED FROM: ( http://www.webmd.com/cold-and-flu/10-immune-system-busters-boosters )