A robust immune system is the holy grail of good health—fending off infections, helping us bounce back from injuries, and helping to reduce the likelihood of serious conditions such as shingles and even cancer. And this intricate network of molecules, cells, tissues, and organs usually operates pretty effectively, given the barrage of assaults from germs, pollutants, and other substances and situations it has to endure on a daily basis.

But as you get older, your immune system weakens and “produces fewer lymphocytes, specialized cells that help our bodies recognize and destroy invaders,” says Janko Nikolich-Zugich, M.D., Ph.D., chairman of the department of immuno­biology at the University of Arizona in Tucson. As a result we gradually become more prone to infections (people 65 and older account for 80 to 90 percent of flu-­related deaths in the U.S.) and slower to heal from wounds, including those from surgery. Plus our immune system’s response to protective vaccines becomes less vigorous.

Over the years, countless dietary supplements, alterna­tive remedies—such as kombucha, a fermented tea—and foods such as mushrooms and oysters have been touted as immune-system boosters. In fact, more than 1,000 supplements currently on the U.S. market are claimed to have a positive effect on immunity.

But a single solution for a flagging immune system in otherwise healthy people has eluded us. “The proof of any purported immune booster is whether it can increase your resistance to infections,” says Marvin M. Lipman, M.D., chief medical adviser to Consumer Reports. Vaccines can help, but “no dietary supplement or alternative remedy has so far been shown to do so.”

So, what can you do to help maintain health as your immune system naturally declines? “The strength of the immune system is tied to a healthy lifestyle, exercise, good nutrition, and sufficient rest,” Nikolich-Zugich says. Some surprising mood-­improving strategies may also make a difference. We reviewed recent research and asked leading experts to help us separate fact from fiction.

Eat Smart

Try for variety in your diet. “Our immune system depends upon having all the essential nutrients in the right balance for its optimal function,” says Walter Willett, M.D., Dr.P.H., chairman of the department of nutrition at the Harvard School of Public Health. For example, people whose diets are low in iron; selenium; vitamins A, C, and D; and several of the B vitamins may have fewer white blood cells—our immune system’s first line of defense against disease.

And the white blood cells they do have may be less active. To ensure that you’re getting what you need, aim for as many types and colors of fruits and vegetables as you can, along with whole grains, lean protein, low-fat dairy, and healthy oils.  

Consume alcohol only in moderation. Though a modest amount of alcohol appears to improve the immune response, too much “turns off genes that help defend us against microbes and turns on genes that make us vulnerable,” says Ilhem Messaoudi, Ph.D., associate professor of biomedical sciences at the University of California, Riverside.

In a recent study in the journal Alcohol, binge drinkers (women who consume four drinks within 2 hours, or men who consume five) had fewer disease-­fighting natural killer cells. They also had higher levels of cells that encourage the immune system to be less active. What does moderate mean? One drink per day for women or two for men.

Consider a D supplement. Because studies have shown that vitamin D plays an important role in the immune system and older adults are at risk of developing an insufficiency, a daily supplement of 800 international units (IU) may be worthwhile. But skip supplements of other nutrients unless you have a diagnosed deficiency.

Don’t megadose on supplements. Large doses of supplements such as vitamin A, iron, and others can actually hamper the immune system. For example, for most adults, more than 400 micrograms per day of folate, a B vitamin, may impair our natural killer cells. And though we may have some difficulty getting enough zinc in our diets—and trouble absorbing it properly as we age­—100 milligrams or more per day can weaken the immune system.

Adopt Good Habits

Get your zzz’s. Sufficient sleep appears to help our immune system fight off viruses, according to research led by Sheldon Cohen, Ph.D., director of the Laboratory for the Study of Stress, Immunity and Disease at Carnegie Mellon University in Pittsburgh. In a recent study in the journal Sleep, Cohen’s team tracked 164 people’s sleep habits for a week, then infected them with a rhinovirus (which can cause colds). People who slept less than 6 hours per night were significantly more likely to develop a cold than those who slept for more than 7 hours. So get 7 to 8 hours of shut-eye per night—a good amount for keeping our immune system in good working order, Cohen says. (See our advice on choosing the best mattress for you.)

Exercise … but don’t overdo it. Physical activity may lessen the likelihood of upper respiratory infections and severity of symptoms if you do get one. According to Jeffrey A. Woods, Ph.D., director of the Center on Health, Aging, and Disability at the University of Illinois at Urbana-Champaign, moderate exercise may bestow those benefits by reducing inflammation in the body. So aim for at least 30 minutes of moderate aerobic exercise—such as brisk walking, cycling, swimming, or jogging—or working out on a treadmill three to five days per week. More isn’t necessarily better. Intense and prolonged exercise may suppress immunity, Woods says.  

Kick butts. Not only does smoking tobacco (and exposure to secondhand smoke) increase your risk for lung cancer, COPD (chronic obstructive pulmonary disease), and heart disease, but it also makes it more difficult for your immune system to fight off invading organisms. (See our advice on the best ways to stop smoking.)

Relax and Enjoy

Cultivate life’s ‘wow’ moments. “People who experience awe more frequently have lower levels of pro-inflammatory proteins in their body,” says Jennifer E. Stellar, Ph.D., a researcher at the University of Toronto. Short-term inflammation helps your body fight invading germs, but persistent inflammation has negative effects on health and immunity.

In a recent study in the journal Emotion, Stellar and colleagues at the University of California, Berkeley, assessed the emotions of 94 college freshman over the course of a month. They found that students who experienced positive emotions—especially awe—had the lowest levels of a protein called interleukin-­­6, a marker of inflammation. A variety of experiences, from gazing at art to attending a symphony to cradling a newborn, can conjure up a feeling of awe.

Indulge in a massage. In addition to easing muscle tension, massage “has profound effects on the immune system,” says Mark Rapaport, M.D., chairman of psychiatry and behavioral services at Emory Healthcare in Atlanta. Researchers at Emory University and the University of California, Los Angeles, found that compared with the effects of gentle touch, a weekly Swedish massage over five weeks boosted the number of health-protecting white blood cells and natural killer cells. It also reduced the number of cytokines, substances that are associated with inflammation.

Nurture friendships. The more social connections we have, the less likely we are to develop respiratory infections. In an earlier study, Cohen assessed the social connections of 276 people ages 18 to 55, infected them with rhinovirus, and quarantined them for five days. People with one to three connections had more than four times the risk of developing a cold than those with six or more. It’s the diversity of connections (people we associate with at work, in religious groups, at book clubs, or while volunteering, for example), rather than the sheer number, that appears to exert the protective effect, Cohen says.

And consider this: When Cohen and colleagues exposed 404 adult volunteers to rhinovirus or influenza, they found that the more hugs study subjects received when they were tense or experiencing conflict, the less likely they were to become ill. “All you need is one really good support person to get a buffering effect,” Cohen says.

Ease stress. A 2012 study in the journal Brain, Behavior, and Immunity, co-written by Michael R. Irwin, M.D., found that mindfulness-based stress reduction (individual and instructor-led meditation plus yoga), may lead to lower levels of inflammation in the body. Other research has found that meditative exercise such as tai chi may improve our response to vaccines. For example, when older adults combined vaccination and 40 minutes of tai chi three times weekly for 16 weeks, they had levels of immunity to the varicella zoster virus (which causes chickenpox and shingles) comparable to those of 30- to 40-year-olds, according to a study in the Journal of the American Geriatrics Society.

Ideally, says Irwin, director of the Cousins Center for Psychoneuroimmunology at UCLA, aim for 30 to 40 minutes per day of meditation and yoga, or tai chi. If you’re short on time, 15 to 30 minutes of yoga or tai chi or 10 minutes of meditation at least three times per week can help.

Visit a park. “Nature doesn’t just have one or two active ingredients—it’s more like a multivitamin that provides us with the nutrients we need to protect us from different diseases,” says Ming Kuo, Ph.D., director of the Landscape and Human Health Laboratory at the University of Illinois at Urbana-Champaign. In fact, in a recent review in the journal Frontiers in Psychology, Kuo identified more than 20 ways in which experiencing the great outdoors can improve health. For example, being surrounded by nature reduces the body’s fight-or-flight response to stress, allowing the immune system to rest and recharge.