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.
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.
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.
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.
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. More on omega-3s.