Lack of Sleep
Not getting enough sleep can make you more likely to catch viruses or germs. And you also may take longer to get better. That’s because your body can’t make as many infection-fighting cells and proteins called antibodies that help defend against illness. Your body releases certain proteins that help the immune system, called cytokines, only during sleep.
Anxiety
Stress and worry aren’t great germ fighters. Just having anxious thoughts can weaken your immune response in as little as 30 minutes. Constant stress takes an even bigger toll and makes it harder to fend off the flu, herpes, shingles, and other viruses. Talk to your doctor if you can’t shake your worry or if it gets in the way of normal life.
Low Vitamin D
You may know you need it for strong bones and healthy blood cells. But vitamin D also helps boost your immune system. You can get it in eggs, fatty fish, and fortified foods like milk and cereal. Sunlight is another key source. In the summer, just 5-15 minutes of rays on your hands, face, and arms 2-3 times a week usually is enough. In the winter, you might need a bit more.
Certain Medications
They include drugs to treat allergies, arthritis, lupus, IBS, and organ transplant. Corticosteroids are one example, as are TNF inhibitors for inflammation and chemotherapy for cancer. Talk with your doctor before you adjust any prescription medication.
Too Few Fruits and Veggies
These foods may help your body make more of the white blood cells you need to fight off infections. Fresh produce and nuts and seeds pack a lot of zinc, beta-carotene, vitamins A, C, and E, and other nutrients you need for a healthy body. Plant-based foods also fill you up with fiber, which helps lower your body fat percentage, which can strengthen your immune response.
Source: https://www.webmd.com/cold-and-flu/ss/slideshow-how-you-suppress-immune-system
