Whether you’re feeling a little run down after the holidays, or your immune system always takes a hit during the winter months, here are five must-have winter supplements that will carry you through the season and keep your immune system working at its best.

 Vitamin D

With winter starting to really take hold, the first thing you need to do is to make sure you are maintaining your vitamin D levels. Studies show that vitamin D levels fall during the winter months, and this hormone-like vitamin is absolutely crucial for immune function. One of the ways in which vitamin D works is by facilitating the development of a specific immune cell known as a natural killer (NK) cell, a cell found in particularly high numbers in the respiratory tract, and one of our first lines of immune defense against viruses.[1]  Vitamin D levels are typically the lowest in March—which also happens to be one of the times our immune system is the weakest.[2][3] A reasonable target level for blood levels of vitamin D based on current research is 40-65 ng/mL (100-160 nmol/L).

Mushrooms

Given the value of NK cells for protecting the respiratory tract, it’s worthwhile to focus on supporting the function of these cells during the winter. One of my favorite foods for enhancing NK cell function is mushrooms. In fact, there are a few specific mushroom extracts that have been studied to boost NK cell function. One particular mushroom extract that stands out is called active hexose correlated compound (AHCC). One study, published in the Journal of Nutrition, found that supplementation with this bioactive compound made from shiitake mushrooms enhanced NK cell function, number, and immune defenses in the lungs.[4]

Garlic

For thousands of years garlic has been used to modulate inflammation, support a healthy microbial balance, and prime the immune system. The sulfur-containing compounds in garlic—especially aged garlic extract—are thought to be the primary factors in garlic that support immune function.[5] Garlic appears to support a healthy inflammatory response and supports the function of several different immune cells including macrophages, NK cells, and neutrophils. It also supports a healthy bacterial balance in the digestive tract—where a large amount of our immune system is located.[6] [7]

Echinacea

When we are under stress, our adrenal glands secrete the hormone cortisol which suppresses the immune response. One herb that has been shown to help support the immune system during times of stress is echinacea, especially Echinacea purpurea.[8] Indeed, there are nine known species of echinacea, all of which are native to North America, and only a few have been studied for immune function, making it important to get the right type of echinacea if you’re looking for immune support. Studies suggest that Echinacea angustifolia, Echinacea purpurea, and Echinacea pallida are the best species for immune function.[9]

Vitamin C

You don’t have to be a nutrition expert to know that vitamin C is important for immune function, but you might be surprised to hear why. First and foremost, vitamin C is required for the synthesis of collagen, the structural glue that keeps our tissue barriers (i.e., the skin, mouth, lungs, and digestive tract) healthy and strong. Having strong barriers helps keep unwanted microbes from getting in, ultimately acting as an important immunological defense. Additionally, vitamin C provides antioxidant support to immune cells themselves. Immune cells produce free radicals as ammunition to kill bacteria and viruses, but these free radicals can also damage the immune cells. But immune cells are smart—they gobble up vitamin C when they are activated, dramatically increasing their intracellular stores of this antioxidant, which protects them from this collateral damage. 

There’s a lot of reasons we get run down in the winter—stress from the holidays, excessive travel, a lack of sleep, too little physical activity, and eating too much sugar can all contribute to a weak immune system. If you want to stay in tip-top shape through the winter season, it’s important to address these lifestyle issues (Get moving! Nix the sugar!), eat the right foods, and support your immune system with these must-have winter supplements.

Looking for delicious, kid-friendly meals that include lots of immune supportive nutrients? Try these recipes.

Want to learn more about the immune system and how different foods can help boost natural killer cell function? Listen to this great podcast featuring Ben Greenfield and yours truly.