These nutrition tips and guidelines can help keep your immune system strong.
What Is Ascorbic Acid?

These nutrition tips and guidelines can help keep your immune system strong.

A strong, well-functioning immune system is the cornerstone of good health, fighting off disease and infections and allowing you to recover more quickly if you do get sick. And despite the claims you see on some food and supplement labels, there is no specific food or nutrient that has been clinically proven to "boost" the immune system all on its own. Rather, you need a variety of foods that provide a natural abundance of vitamins, minerals and phytonutrients (compounds found in plants that have disease-fighting properties); all those nutrients work together to keep your immune functions running smoothly. And it's not all about food, either: studies show that regular exercise, even something as simple as a daily 30-minute walk, can improve immune functioning. Maintaining good sleep habits can help too.

The best nutritional strategy for keeping your immune system strong, then, is to have a well-nourished, well-rested body and move it regularly. Follow these tips from the nutrition experts at EatingWell to keep your system fully charged.

Get enough vitamin C

Your body needs vitamin C to build and maintain healthy skin-your body's first line of defense in preventing disease and infection. The vitamin is also critical for producing white blood cells and antibodies that fight off infections, and it is a powerful antioxidant that helps protect cells from free-radical damage.

While vitamin C has long had a reputation for helping prevent the common cold and many people gulp megadoses when they feel cold symptoms coming on, clinical studies have shown no effect for vitamin C in cold prevention in normal situations. However, in a handful of studies the vitamin did appear to slightly reduce the duration of a cold, as well as the symptoms.

The best way to get enough vitamin C is by enjoying it in foods, not pills. It's easy to do: just one large orange or a cup of orange juice will meet your daily needs. You'll get more nutrition in the bargain: foods high in vitamin C tend to also be rich in other immune-protective compounds.

When you're looking for vitamin C, think outside the orange crate. Cantaloupe, grapefruit, honeydew melon, kiwi, mangoes, papayas, raspberries, starfruit, strawberries and tangerines are all rich in the vitamin. In fact, each serving supplies at least 25 to 30 percent of recommended amounts of vitamin C for a day. And don't forget that many vegetables, including broccoli and peppers, are terrific sources. Aim for at least six servings of fruits and vegetables a day, including at least one that is rich in vitamin C.

Grab some carrots

Beta carotene is an orange-yellow pigment found in many fruits and vegetables, carrots most famously. Your body converts beta carotene as it's needed into active vitamin A, a nutrient important for overall good health and immune functioning. Beta carotene is also a powerful antioxidant that helps protect cells from the damage of free radicals (unstable molecules that arise as by-products of cell metabolism).

While beta carotene might have the most name recognition, it is only one member of a large family of compounds called carotenoids that have numerous health and immune benefits. (Lutein, found in egg yolks, corn and leafy vegetables, and lycopene, most familiar in red fruits and vegetables like tomatoes and watermelon, are also in the carotenoid family.) Researchers believe that carotenoids work together in promoting health and preventing cancer. This is why getting carotenoids in food may be more beneficial than taking beta carotene supplements.

There has been a lot of conflicting research regarding the benefits of beta carotene and vitamin A in the prevention of cancer, cardiovascular disease, vision and aging. Although both beta carotene and vitamin A are beneficial and important for a strong immune system, supplementing with too much of either can have unintended negative health consequences; for example too much supplemental vitamin A is associated with increased risk of bone fractures. The current consensus is that eating plenty of beta carotene-rich foods is safe, and beneficial to overall health and maybe immunity, but taking a large-dose supplement of either beta carotene or vitamin A is not recommended and may even be harmful. There are plenty of delicious food sources of beta carotene, including oranges, papayas, tangerines and peaches, as well as red peppers, sweet potatoes and carrots.

Eat (don't pop) your antioxidants

Antioxidants protect cells in the body from oxidation, a process that leads to cell damage. Oxidation may play an important role in atherosclerosis, or hardened arteries-the development of plaque in blood vessels that can cause high blood pressure, heart disease and stroke.

Eating foods rich in antioxidants-including vitamins E and C, carotenoids and selenium-may bolster your immune system, lower your risk of heart disease and protect against cancer. According to studies, however, taking extra antioxidant pills probably has no benefit. The current recommendation by the American Heart Association is to make sure you include these important nutrients in your diet, but not to take supplements. Aim for a more plant-based diet, and you're sure to get plenty: the most antioxidant-rich foods are from the plant kingdom, including fruits, vegetables, whole grains, nuts and seeds.

Get mineral happy

Selenium is essential for a strong immune response and to fight infection. Studies suggest that very ill people or those with compromised immune systems can benefit from additional selenium, however otherwise healthy people are not likely to need extra doses. The mineral, found mostly in mushrooms and whole grains, may also reduce risk of some cancers. Best food sources of selenium are seafood: tuna, red snapper, lobster and shrimp. Other good food sources of this mineral include chicken (white meat), whole grains, brown rice, egg yolks, cottage cheese, sunflower seeds, garlic, Brazil nuts and lamb chops.

Think zinc

Zinc is another mineral important to a healthy immune system, and people who are deficient tend have a poorer immune response. Zinc is needed to produce and activate some types of white blood cells that help fight infections, and studies show that when zinc-deficient people are given zinc supplements, their immune functioning improves. Zinc has long been promoted as a nutrient that can lower the severity and incidence of the common cold, but clinical trials with the mineral have yielded inconsistent results. What's more, too much supplemental zinc (more than 75 milligrams per day) can actually inhibit immune function, and larger doses can be toxic. It's safest to stick to getting zinc from your diet. Aim for 15 to 25 milligrams a day. Zinc-rich foods include oysters, vitamin and mineral-fortified cereals (such as Total), crab, beef, dark-meat turkey and beans. Find more information on zinc and zinc-rich foods in our nutrient library.

Fill up on whole grains

Whole grains are rich in fiber, vitamins, minerals and hundreds of phytochemicals. They contain several substances that have each been linked to lower cancer risk, including fiber (both soluble and insoluble), antioxidants, phenols and phytoestrogens.

Because of the wide range of anticancer ingredients they contain, diets high in whole grains may decrease cancer risk in general. When data from 40 studies on whole grains and cancer risk were combined and analyzed recently, researchers found the risk for cancer was reduced by 34 percent on average in people who ate large amounts of whole grains compared to those who ate small amounts. Looking for a good whole-grain cereal to start your day? Click here for advice.

Consider flax

Flaxseeds, which look like darker, larger cousins of sesame seeds, are one of the few plant sources of omega-3 fatty acids-the heart-protective compounds more commonly associated with fatty fish. The form of omega-3s found in flax, called alpha linolenic acid, or ALA, may offer some protection against heart disease and some cancers (though studies show its heart-protective effects are not as powerful as fish-based omega-3s).

Flaxseeds are also nature's best source of lignans, plant compounds that have estrogenlike activity in the body. (Flaxseed oil, extracted from the seeds, doesn't naturally contain these so-called phytoestrogens, but some manufacturers may add them.)

Currently, scientists are researching the possibilities of flaxseed as a cancer preventer. In a few small studies, flax seemed to offer some protection against estrogen-receptor-negative breast cancers, and preliminary laboratory work suggests a possible role in inhibiting colon, breast, skin and lung tumors. When it comes to prostate cancer, however, the picture is more complicated- with some studies showing that taking flaxseed can increase risk, while others show a reduced risk.

Look for flaxseed in supermarkets and natural-foods stores. It's available as flaxseed flour, meal, oil and whole flaxseeds. The whole seeds can't be digested and need to be ground before you use them. Once ground, they go rancid quickly, so buy ground flax (or grind it yourself in a clean coffee grinder) in small batches only and store in the refrigerator. Flaxseed oil, even more perishable, also belongs in the refrigerator and shouldn't be used if it smells like paint-a signal it has gone rancid.

Get enough sleep

Getting enough sleep is important to your health because it boosts your immune system, which makes your body better able to fight disease. So how many hours of sleep are enough for you? Experts say that if you feel drowsy during the day-even during boring activities-you are not getting enough sleep. Also, quality of sleep is just as important as quantity. If you wake up often during the night you are not getting good-quality sleep. If you experience frequent daytime sleepiness, even after increasing the amount of quality sleep you get, talk to your doctor. He or she may be able to identify the cause of sleep problems and offer advice on how to get a better night's sleep. Can what you eat or drink help you sleep better? Click here to find out.

Eat healthy fats

Your body needs an adequate amount of healthy fats to help you absorb fat-soluble nutrients and to maintain good overall health and a healthy immune system. Look for healthy fats in monounsaturated and polyunsaturated oils and foods like fatty fish, olives, nuts and avocados.

When it comes to your immune system, vitamin E is especially important for proper functioning. Wheat germ oil, sunflower seeds and sunflower oil, almonds, safflower oil and hazelnuts are all excellent sources of vitamin E, so there's no need for most people to pop a supplement. Not long ago, vitamin E supplementation was touted as beneficial to heart health, immunity and cancer prevention. But subsequent clinical studies failed to show a benefit-and we now know that people should get this beneficial nutrient from food rather than a supplement. Too much vitamin E could have unintended health consequences, including an increased risk of bleeding and impaired blood clotting. People taking anticoagulant drugs, or those who are deficient in vitamin K, should avoid taking supplemental vitamin E.

The role of omega-3 fats (those found in fatty fish, nuts and flaxseeds) in immunity is also being actively studied. And while it appears that omega-3 fats are beneficial to a healthy immune system, the mechanism is still poorly understood. But including good sources of omega-3 fats in your diet has many benefits for your heart and overall health.