Tis the season of giving… germs and viruses, that is. Is it something in the air or does seemingly everyone catch a cold the moment temperatures drop below 60ºF? According to science, you’re not wrong.

Indeed, wintertime is often fraught with sniffles, sneezes, and sickness (hi, flu season). But this may be no coincidence after all: research shows that cold, flus, and other respiratory illnesses are statistically even more prevalent come this time of the year. So, how can we prevent the almost inevitable wintertime cold from getting the best of us? Ahead we’re sharing several science-backed ways to boost immunity to stave away illness while everyone else is bedridden with a box of tissues, according to a longevity doctor and a registered dietitian.

3 common factors that can weaken your immune system

First things first: a primer on immunity.“Our immune system is comprised of a variety of cells, tissues, and organs in the body, working together to protect against foreign invaders before they cause harm, to fight harmful pathogens—bacteria, viruses, fungi—if they are present, and to remove them from our body to maintain health and balance,” says Melanie Murphy Richter, MS, RDN, a registered dietitian and neuronutritionist. Ahead are three common culprits that can weaken this delicate ecosystem.

1. Changes in temperature

According to Reuben Chen, MD, a board-certified sports medicine physician, pain management expert, and chief medical advisor at Sunrider International, changes in weather—hot or cold—can affect the immune system, making it more susceptible to colds, the flu, and other upper respiratory infections.

What’s more, as folks hunker down to brace for the chilly weather, they often spend more time indoors, making germs and viruses more likely to spread from person to person. Plus, studies show that even the slightest temperature drop can negatively affect our ability to stave away viral infections harboring in our nasal passageways.

2. High stress levels

Several major holidays fall during this time of year, making our chances of contracting something along the way even more likely. Aside from the increased person-to-person contact between traveling and gatherings, stress levels can also be running high. “Stress is a common factor in needing an extra immunity boost. With traveling—which exposes you to new environments and new pathogens—family gatherings, and looming end-of-year work goals, all these are major causes for weakening the immune system, and can send your stress level into overdrive,” Dr. Chen says.

3. Changes in diet that primarily affect the gut

Another factor that contributes to your immune health? Your eating habits. “Poor diet and increased alcohol consumption can fuel the need to ramp up your body’s immune defense,” Dr. Chen says.

Meanwhile, Richter notes that more than 70 percent of our immune system lives inside of the gut. “Not only do the presence of certain microbes living in our gut play a critical role in maintaining the balance of our immune system, the gut also holds our ‘adaptive immunity,’ our immune system’s memory bank, and the gut lining and epithelial cells found in the gut act as our body’s first line of defense,” Richter says. “By supporting gut health, you’ll be boosting your gut health.”

The dietitian also explains that some holiday foods may be filled with refined sugars “which can alter gut composition in favor of pathogenic bacteria.” In addition, she explains that fluctuations in sugar levels can also influence cortisol, a stress hormone. In turn, the combination of increased quantities of cortisol and a compromised gut can lead to a weakened overall immune system.

5 science-backed ways to boost immunity 

1. Increase fiber intake throughout the day

One of the top ways to boost immunity according to Richter is by consistently keeping up with adequate fiber intake. “Dietary fiber—like that found in fruits, vegetables, nuts, seeds and whole grains—contain the prebiotic fibers that the good microbes in our gut eat to stay alive and function,” she says. “Eating more of these prebiotics fibers have been shown to increase our body’s ability to create butyrate and other short-chain fatty acids (SCFA) that play a critical role in reducing overall inflammation, providing fuel for our gut, and also impacting the expression of certain genes that are involved in inflammation and the immune system.”

Keep in mind that increases in fiber should be introduced slowly and steadily over time to prevent stomach irritation. “This should not be considered a spot-treatment when sick,” Richter says.

2. Add a probiotic to your daily routine

According to Richter, probiotics and immunity go hand in hand. “Taking certain probiotics can support innate immunity, our immune system’s first line of defense against certain harmful pathogens. Certain strains of probiotics—like those in the Lactobacillus and Bifidobacterium families—can help to support this system to help reinforce our epithelial walls—gut lining—and stimulates the production of important cytokines—immune cells—that are released in response to the presence of a pathogen,” Richter says.

3. Decrease refined sugar consumption whenever possible

Richter notes that refined sugar consumption should be kept to a minimum whenever possible as it can have a profound impact on gut health. “Reducing processed and refined sugars can improve gut function and immune system. Excessive consumption of sugar, especially those found in processed and refined sources, have a negative impact on gut health and overall immune system,” she says. “Not only do these refined sugars alter the composition of the gut to favor more pathogenic microbes, but they also increase the permeability of our gut, making it easier for pathogens to enter our system.”

4. Exercise regularly

Lastly, according to Dr. Chen, exercise is one of the best ways to help boost your immunity from within. “Moderate exercise can stimulate cellular immunity by increasing the circulation of immune cells in the body. Research has shown that exercise acts as a modulator of the immune system, and done regularly, can lower chances of catching viral infections, like the common cold,” he says.

5. Ensure you’re eating a well-balanced diet

Dr. Chen recommends eating a diet that includes a wide variety of foods from different sources, such as fruits, vegetables, meats, and carbohydrates, to name a few. “This will help provide a wider array of micronutrients and macronutrients, along with vitamins and minerals needed for a healthy immune system,” he says. His go-to meal for immunity includes mixing together carrots, dark green leafy greens, apples, oranges, and green and red bell peppers, along with salmon and sliced almonds.

On that note, Dr. Chen also reminds us that a well-balanced diet wouldn’t be complete without adequate hydration. “Drinking enough water to help flush out the waste in the body is just as important a way to help boost your immune system.”

Best foods for boosting immunity, according to an RD: