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It would be great if there was an over-the-counter supplement that would boost your immune system enough to prevent a cold or the flu. Unfortunately, according to Harvard Medical School’s Harvard Health, there are no proven benefits to supplements for the immune system. In fact, the whole idea of boosting your immune system is wrong. 
Your immune system is an intricate and complex system that works best when it is in perfect balance. Boosting it can lead to an overactive immune system, which actually makes immune health worse. An overactive system can lead to allergies and inflammatory diseases of the immune system. However, there are some things you can do to support your immune system and keep it in balance. [1-3]
How to Support Your Immune System
There are two ways to support your immune system that have been studied or are being studied. First, there is good evidence for taking vitamins and minerals, and there are ongoing studies for probiotics. Probiotics may help provide healthy bacteria to your gut microbiome. A balanced microbiome has been linked to immune system stability, but the jury is still out on the benefits of probiotics for the immune system.
Foods to Support Your Immune System
Vitamins and minerals do help, and the best way to get them is from food, not supplements. If you are elderly or unable to maintain a healthy diet, a multivitamin with minerals may be an option. Otherwise get your immune system support from these sources:
- Vitamin C from citrus fruits, strawberries, spinach and leafy green vegetables, bell peppers, Brussels sprouts, and papaya
- Vitamin E from nuts and seeds like almonds, peanuts, hazelnuts, and sunflower seeds
- Vitamin A from fish, meat, dairy, carrots, sweet potatoes, squash, cantaloupe, and leafy greens
- Vitamin D from cold water fish like salmon, mackerel, tuna, and sardines, as well as fortified milk, juice, and cereals
- Vitamin B (folic acid) from lentils, beans, leafy greens, avocado, and enriched pasta, bread, or rice
- Iron from red meat, poultry, shellfish, beans, leafy greens, fortified cereal, and canned sardines, or tuna
- Selenium from animal foods including seafood, meat, poultry, and dairy,
- Zinc from animal foods like shellfish, meat, poultry, and from chickpeas or baked beans 
Make Lifestyle Changes to Support Immune Health
The other best way to support your immune system is to stay healthy, which takes a lot of pressure off your immune system. These are the key lifestyle support strategies:
- Wash your hands frequently, this will reduce germs entering your body.
- Stay physically fit and maintain a healthy weight with exercise.
- Reduce your stress level. Stress causes inflammation which weakens your immune system.
- Get enough sleep. Research shows the being sleep-deprived weakens immunity.
- Stop smoking and drink alcohol only in moderation, which is a limit of one drink a day for women and two for men [1-3].
Finally, the one thing that might actually be a beneficial boost to your immune system is getting your vaccinations. Ask your doctor about a vitamin and mineral supplement if you can’t maintain a healthy diet or lifestyle.
Do Herbal Supplements Boost Immunity?
As for any herbal supplements to boost immunity, keep in mind these guidelines from the National Institutes of Health:
- Scientific evidence supporting these supplements are limited and benefits may not be supported by evidence.
- Supplements in stores may not be the same as supplements in research studies.
- Supplement ingredients are not regulated by the FDA, what you are actually taking may be different from what you see on the label .
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- Harvard Heath, Can supplements help boost your immune system? – Harvard Health
- Cleveland Clinic, 8 Vitamins & Minerals You Need for a Healthy Immune System – Health Essentials from Cleveland Clinic
- Mayo Clinic, Building Immunity – Self Care in Times of Difficulty | Mayo Clinic Connect
- NIH, Dietary and Supplements, Dietary and Herbal Supplements | NCCIH (nih.gov)