Ever since the days of scurvy outbreaks, it's become common knowledge that vitamin C is a key nutrient for the immune system. According to a review in Nutrients, it contributes to the rapid increase in B cells and T cells, two white blood cells that play a role in secreting antibodies and killing off infections.
Although taking high doses of vitamin C is believed to prevent illness, research suggests otherwise. A review in the Cochrane Database of Systematic Reviews found that taking at least 200 milligrams of vitamin C per day only reduced the risk of contracting a cold in extremely active people, like marathon runners and skiers. For the average person, large doses of vitamin C don't reduce the risk of catching a cold. That said, taking in at least 200 milligrams of vitamin C per day may lessen the duration of cold symptoms by 8 percent (or about one day) in most people.
Luckily, vitamin C is abundant in fruits and vegetables. Eating a well-balanced diet with all the colors of the rainbow will help you get the recommended 65-90 milligrams per day. And while vitamin C deficiencies are rare, they may occur if consumption drops to less than 10 milligrams per day, according to the National Institutes of Health.
According to a study in Molecular Medicine, zinc is pivotal in the development of neutrophils and natural killer cells, both of which aid in healing wounds and fighting infections. Although zinc won't prevent you from catching a cold, review of the literature published in Cochrane Database of Systematic Reviews suggested that taking zinc at the onset of a cold might decrease its duration.
Good sources of zinc include beef, oysters, crab, cashews, chickpeas, Greek yogurt, pumpkin seeds and lentils. Since zinc isn't as prevalent in a lot of foods, deficiencies can occur, especially among vegetarians and vegans. With a zinc deficiency, the body produces fewer infection-fighting cells, which increases your chance of getting sick. That's why it's important to get the recommended 8-11 milligrams per day to keep the immune system functioning properly, noted Nutrients.
Although not an essential nutrient, probiotics — or the "good bacteria" in your gut — have been shown to affect overall immune health. Probiotics influence the microorganisms that live in the digestive tract, where 70 percent of the immune system is housed, and can help strengthen intestinal immunity. Probiotics initiate responses by macrophages, a type of cell that engulfs harmful substances and rids them from the body. Microbial agents may suppress inflammation in the lungs and replication of viruses.
There's no set number of probiotics that anyone should have in any given day. That said, eating plenty of fermented foods is an easy way to incorporate them into your daily diet. Yogurt, kefir, kimchi, sauerkraut, miso and tempeh are all good sources of probiotics.
Vitamin E is a fat-soluble vitamin that's one of the most important antioxidants in biological membranes of all cells. Vitamin E protects against oxidative damage of the immune cells and strengthens their physiological function.
According to a review in Nutrients, when supplemented, vitamin E has been shown to increase the percentage of T cells, the white blood cells that seek out and destroy harmful invaders. The recommended daily dose of vitamin E is 15 milligrams. You can get this important vitamin through almonds, sunflower seeds, spinach, broccoli, tomatoes and avocados.