With cold and flu season right around the corner, it’s a good time to boost your immune system to fight off viral and bacterial infections, and other nasty bugs.

Despite what your mom may have preached, you won’t get sick just from being outdoors in the cold. But researchers say that we spread infections more easily in winter months simply because we spend more time together in close quarters inside.

In fact, getting outside is one easy way to prime your immune system. That’s because you can sop up vitamin D from the sunshine, even in winter.

Scientists at the University of Copenhagen found that the immune system’s killer T cells are activated by vitamin D and aren’t effective fighters without it. Just beware that, even in colder months, the sun’s rays can still damage your skin. So limit your exposure to no more than 15 to 20 minutes each day.

Here are some other natural ways you can bolster your defenses:

Chill out: Chronic stress can ravage the immune system, concludes a mega-analysis of nearly 300 studies. Learn how to relax through meditation, deep breathing, yoga, a hot bath, some soothing tea, cuddling with your kitty, or whatever it takes to give you an extended moment of peace.

Consume chicken soup: This one your mom’s right about. University of Nebraska researchers found that the so-called Jewish penicillin inhibits the migration of white blood cells, which reduces congestion. When made with veggies like onion, garlic, celery and carrots, chicken soup also contains a blend of vitamins, minerals, antioxidants and amino acids that support immunity. Throw in a few shitake mushrooms for a super-boost.

Exercise: On winter days it may be tempting to curl up on the couch and binge-watch “Game of Thrones,” but you’re better off moving your butt. According to Harvard Health Publications, exercise promotes good blood circulation, which helps transport the soldiers of your immune army around your body so they can smite invaders.

Sleep well: Try to get seven to nine hours of shut-eye a night. “A lot of studies show our T cells go down if we are sleep deprived,” Houston-based sleep expert Dr. Diwakar Balachandran says on WebMD.com. “And inflammatory cytokines go up. This could potentially lead to the greater risk of developing a cold or flu.” If you do get sick, getting a lot of sleep will help you recover faster.

Limit vices: Smoking and drinking both deal blows to the immune system. Cigarette smoke not only damages antibodies and antioxidants but also paralyzes the little cilia in your nose that help filter out pathogens. Meanwhile, a couple of drinks may not hurt you. But researchers at Loyola University Health Systems found that too much beer or booze turns the immune system sluggish.

Eat yogurt: Actually, any fermented food or high-quality probiotics will work to build up your natural defenses. A study published in the American Journal of Clinical Nutrition says the “live and active cultures” in yogurt help to stimulate the immune system. They can also replace the “good” bacteria in your gut that you lose when taking antibiotics, which, by the way, do nothing to fight viral infections such as a cold or flu.

Order surf and turf: Steak and shellfish, including lobster, crabs, oysters, clams and mussels, are loaded with zinc. A study published in Autoimmunity Reviews found that a zinc deficiency has a negative impact on several types of antibodies, particularly T cells.

Drink green tea: A potent polyphenol antioxidant in green tea was found to boost levels of a key antibody, according to researchers from the Linus Pauling Institute at Oregon State University. “This appears to be a natural, plant-derived compound that can affect the number of regulatory T cells, and in the process improve immune function,” says principal investigator Emily Ho.

Wash your hands: This may be the simplest way to boost immunity since about 80 percent of all infectious diseases are transmitted by touch. Military recruits assigned to “Operation Stop Cough” reduced cases of respiratory infections by 45 percent just by rigorously washing their hands five times a day.