The immune system is a vast network of cells, tissues and organs that work in tandem to protect your body from bacteria, viruses and other invaders. In most cases, the body does a good job fighting off the bad guys, but quality nutrition and supplementation can assist in keeping the immune system in top form. Try one of these five immune-boosting supplements to stay happy and healthy this fall.

Echinacea: Alleviates Cold Symptoms

This popular Native American herb is in high demand when cold and flu season is in full swing. Although some scientists dispute the benefits of echinacea, there’s plenty of research to support the immune-boosting benefits of this purple, cone-shaped flower. A number of clinical trials have shown that people who take echinacea—300 milligrams, three times daily—at the first signs of a cold reduce the severity of their colds and have fewer symptoms than subjects who don’t use the herb.

Though there are nine species of echinacea, those most commonly used for their medicinal benefits are Echinacea angustifolia, Echinacea pallida and Echinacea purpurea. You’ll find this healing herb in capsules, extracts and soothing teas.

Vitamin D: Protects the Body from Infection

Best known for benefitting bone health, vitamin D can also ward off infections, according to a number of studies.

Exposure to sunlight is the most natural way to absorb vitamin D, but it requires being out in the sun without sunscreen, which could put you at risk for skin cancer, so many experts consider supplementation a better option. The Recommended Dietary Allowance (RDA) for vitamin D for adults up to age 70 is 600 International Units (IU), though most supplements deliver a dose of 1,000 IU, which is well within safe parameters.

The two forms of vitamin D are D2, also known as ergocalciferol, and D3, or cholecalciferol. Vitamin D3 supplements are available in several forms—capsules, soft gels and increasingly popular gummies, to name a few. They’re often made from fish oil, such as cod liver oil, and may contain essential fatty acids as well. Vegetarians may prefer a plant-based vitamin D2 supplement (also available in a variety of forms, including capsules, tablets and oral sprays), although study findings suggest that D3 more effectively raises vitamin D levels in the blood.

Probiotics: Improves Gut Health to Enhance General Health

A daily probiotic can support your gut health. And an increasing amount of research has also shown that a healthy gut can strengthen the immune system, which translates to overall better health.

Two of the most prevalent and well-studied probiotic species are lactobacillus and bifidobacterium, which are found in the majority of supplements on the market.

Probiotic supplements come in capsules, tablets and powders. According to the University of Maryland Medical Center’s Complementary and Alternative Medicine guide, doctors recommend a daily dosing range of 1 billion to 15 billion colony-forming units (CFUs) for maintaining intestinal health.

Zinc: Boosts Your T Cell Levels

An important trace mineral, zinc is essential to immune system health. However, a 2013 study reported that approximately 17 percent of the world’s population is at risk for zinc deficiency because of inadequate nutrition.

While the majority of Americans get zinc from food (some of the best sources are oysters, beef, lobster, pork, baked beans, chicken, yogurt, cashews, chickpeas and oatmeal), some days our diets are lacking. The RDA for zinc for adults is low—between 8 and 11 milligrams per day (mg/day)—so if you take a good daily multivitamin, you’re already set.

Research suggests that slightly more zinc could lower the risk of catching a nasty cold. A recent study published in The American Journal of Clinical Nutrition found that zinc supplementation of 30 mg/day boosted the number of T cells (white blood cells that are critical to a strong immune system) in nursing-home residents.

Astragalus: Stimulates the Immune System and Combats Stress

Astragalus has been used for centuries in Traditional Chinese Medicine (TCM) and is thought to replenish energy or qi, which TCM closely links to immunity. It is also used to treat a number of immunodeficiency disorders that impair the immune system’s ability to fight viruses and bacterial infections, as well as an adjunct to mainstream cancer treatment.

Astragalus is one of many adaptogenic herbs that may be prescribed alone or in combination to help the body deal with stress, a risk factor for a number of diseases.

TCM practitioners recommend daily astragalus supplementation to maintain a healthy immune system, as well as to improve energy and sleep quality. Astragalus is available in a number of dose strengths and formulations, and dose depends on age, weight and other factors, so it is best to work with your doctor to find out what is right for you.

TIP: It’s a good idea to speak with your physician before starting to use any new supplement, particularly if you’re being treated for any medical conditions.