Here's what really determines the strength of your immune system—and what you can do to help it function at its best.

By Jacqueline Andriakos
Updated October 14, 2020
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As an editor at Health, I practice what we preach. I get 7 to 8 hours of sleep most nights, I make it to my favorite workout classes regularly, and I eat all of my servings of fruits and vegetables in every day (okay, I leave room for wine and dessert too).

Yet every year, I manage to come down with several colds, bouts of strep throat, and stomach bugs. I even got shingles a few years ago. My burning question: Why do I keep getting sick, despite doing everything "right"?

The short answer: I may just have a slightly weaker immune system. "I have some perfectly healthy patients who get five to six upper respiratory infections—aka, the common cold, or more rarely, full-blown influenza—a year, and others with the same health profile who hardly ever get sick," says Holly Phillips, MD, an internal medicine physician in New York City and author of The Exhaustion Breakthrough. "It doesn’t seem fair, and honestly it’s not."

Even more, some individuals are also thought to be especially resistant to certain bacterial and viral infections. "Immunologists refer to them as having 'super-immunity,' and their genetic makeup is the focus of an entire field of research," Dr. Phillips says.

See, your immunity is determined by several factors. Genetics play a large role, says Paolo Boffetta, MD, professor of medicine, hematology, and medical oncology at Icahn School of Medicine at Mount Sinai Hospital in New York City. "Immunological genes are many and complex, and your immune response depends on their combined performance," Dr. Boffetta explains.

Experts also believe that you build up immunity while you are young, or possibly even before you are born. "There are factors during infancy and childhood, and perhaps also in utero, that contribute to the development of the immune system, but they are not fully understood," Dr. Boffetta says. What's more, environmental factors, such as pollutants and toxins, may also weaken your immune system over time.

One standout theory for why some people may just be more susceptible to illness is the hygiene hypothesis—the idea that the more bacteria and viruses you come into contact with as a kid, the “smarter” your immune system becomes. The thinking is "keeping kids extra clean and smothering them in hand sanitizer may cause more harm than good in the long run," Dr. Phillips explains.

On top of that, lifestyle factors, including stress, obesity, heavy alcohol drinking, and poor hygiene, can all weaken your immune response and lead to more frequent infections, Dr. Boffetta notes.

How can you strengthen your immune system?

Just because your immunity is not something you can entirely control doesn't mean you should throw caution to the wind and start abandoning your healthy habits—quite the opposite, really.

Start with a look at your diet: Nutrients from fruits and veggies, like zinc, iron, and vitamin C, are essential for a healthy immune system, Dr. Phillips says, as are omega-3 fatty acids. "Omega-3s found in fatty fish, like salmon, also encourage the production of lymphocytes—immune cells that are the front line of defense against infections," she explains. And it's better to get your immune-protective nutrients through food than through supplements, she adds.

Getting plenty of sleep and exercise also helps boost your immune system—whether it feels like these healthy habits are working in your favor or not. Exercise improves circulation; increased circulation boosts the production of germ-fighting antibodies, Dr. Phillips explains. "Exercise also lessens stress, which helps your immune system function at its best," she says.

Sleep is a health-restorative time for the body. "When you sleep, your body releases immune proteins called cytokines, which help fight infections and control the body’s response to stress," Dr. Phillips says. "So a lack of sleep can lead to an under-production of cytokines and other protective immune cells, leaving you more vulnerable to infection."

Your best bet (and mine too, apparently): Stick to the healthy habits you already have in place, and maybe add a few more. But keep in mind that just because you seem to get sick a bit more often, it doesn't necessarily mean you're unhealthy—you're just a bit more susceptible coming down with something.

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