High fat diet

Oils can hinder germ-fighting white blood cells. And high fat diets over time can upset the balance of bacteria in your gut that can help immune response. Look for low-fat dairy with no added sugar, along with lean protein like seafood, turkey, and chicken, or lean cuts of beef with any visible fat cut off. Also, being obese seems to make you more likely to get the flu and other infections, like pneumonia.

Smoking

Nicotine from cigarettes, chewing tobacco, or any other source can weaken your body’s ability to fight germs. Yes, vaping counts, too. And it’s not just the nicotine. Other chemicals in e-liquids seem to suppress your immune response, especially when you inhale them through vaping.

Grief

There is some evidence that sorrow, especially if lasts a long time, can depress your body’s immunity. The effect can linger for 6 months, but may go on longer if your grief is deep or doesn’t ease. Talk to your doctor or a mental health professional if you need help with a loss or traumatic event.

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.

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.