What Weakens the Immune System?

Viral threat

It's unclear why two similar people who become infected with COVID-19 can have very different outcomes: One may develop severe disease while the other becomes only mildly ill. "It's a very difficult question to answer," says David Topham, a professor of microbiology and immunology at the University of Rochester Medical Center.

But for some people, a weakened immune system can leave them more vulnerable to infections ranging from the new coronavirus to the common cold (which is often caused by less deadly types of coronavirus). And there are a number of factors known to undermine immune function. Understanding and addressing those can help fortify your body's defenses.

Medical conditions

Your health status can make a big difference in how well you can fend off viruses and other infections. "Certain underlying conditions are well-known to result in an overall weakened immune system," notes Dr. Ingrid Mayer, a professor of medicine and cancer research at Vanderbilt University Medical Center. Those pre-existing conditions include diabetes, malnutrition and untreated HIV, according to Mayer, as well as some cancers such as leukemia or multiple myeloma.

Separately, autoimmune diseases like rheumatoid arthritis, lupus and multiple sclerosis actually cause the immune system to attack healthy cells, and weaken the body's response to real threats. And although there's buzz around the drug hydroxychloroquine (used for lupus, arthritis and malaria) as a possible treatment for COVID-19, it remains unproven for this purpose.


Various types of medications can impact our ability to fight off infections. Drugs used to treat autoimmune disorders by suppressing the immune system are just one example.

Chemotherapy drugs can also lower immunity, Mayer says, as can steroids, which are used to treat inflammation caused by arthritis and other conditions.

So ask your doctor about all your medication options. And discuss how to treat or mitigate immune-compromising side effects if there are no safe, effective alternatives available.


Lighting up is not only dangerous by itself -- it can also weaken the immune system. In particular, smoking can decrease your ability to fight off diseases that affect the lungs, like COVID-19.

"It affects your airway's ability to clear infection," says Dr. Shira Doron, an infectious disease physician and hospital epidemiologist at Tufts Medical Center in Boston. Although it's still not clear why men appear to be more vulnerable to COVID-19 infection than women, some experts theorize that smoking could be a factor, since men are likelier than women to be smokers, Doron says.

That's just one more reason, in a long list, to never start smoking -- or quit if you do.


Constantly being in fight-or-flight mode is taxing on the body. The strain can be felt in many ways, ranging from raised blood pressure to headaches. Too much work stress can even increase the chances you'll need to take a sick day.

"For anybody, stress is a big factor that can weaken the immune system," Topham emphasizes. Stress can not only increase your vulnerability to infection but it can hamper your recovery time. While there's no way to avoid all stress or anxiety, managing it by taking mental breaks during the day or trying everything from breathing exercises and meditation to yoga can make all the difference.

Sleep problems

Getting too little sleep or poor quality sleep that leaves you feeling tired throughout your day can also undercut your body's defenses.

About 1 in every 3 adults doesn't even get seven hours of nightly shut-eye, according to the Centers for Disease Control and Prevention, the minimum amount recommended. Many others suffer from disorders like sleep apnea that -- even after spending a lot of time in bed -- leave people feeling groggy in the morning.

With many people working at home during the coronavirus pandemic, that could mean some opportunity to rest more -- no need to get up earlier for the work commute, for example. "Maybe people are sleeping in and catching up on their sleep," Topham says. On the other hand, juggling home and work obligations could mean working at all hours and getting less zzz's. Whatever the case, it's critical that you get adequate, restorative rest -- and treat sleep disorders, experts say, so your body's defense system is able to function optimally.


Social distancing -- also now referred to as physical distancing -- can make it hard to connect with others. That, in turn, can put a person at higher risk for mental health challenges, like depression.

In addition, social isolation has been shown to increase stress in animals and people, which is directly linked with a decreased immune response.

For that reason, using all safe options to connect -- via video chat or a simple phone call -- is as important now as ever, experts say.

Poor diet

The traditional Western diet -- high in fat, sugar and processed foods -- isn't exactly an exemplary eating pattern. Not only can it raise the risk of things like heart disease, but it may also inhibit your body's ability to fight disease.

"Bad luck, poor diet, poor sleep habits, tons of stress -- all of those things can be associated with not having optimal immune function," Doron says.

Although you can't control certain pieces of your immunity puzzle, such as genetics, you can control your diet. So doing what you can to bolster immune function may include bucking unhealthy trends at the dinner table. Aim to follow a plant-based diet high in fruits, vegetables, nuts and lean proteins -- akin to, for example, a Mediterranean diet.

Sedentary lifestyle

You could be forgiven for planting yourself on the couch and endlessly scrolling through news updates in the midst of a pandemic. But inactivity and obesity are linked with decreased immunity.

"Being sedentary and not exercising leads to less efficient heart function," Topham says. And he notes there are cases where COVID-19 causes cardiovascular injury that can lead to a form of heart failure that's been deadly in some people with the virus. Obesity can also contribute to heart problems and immune suppression, rendering the body less able to battle viral infections.

Research indicates that regular exercise, on the other hand, boosts immunity and can make you less susceptible to disease, including viruses. Physical activity also helps people manage chronic diseases like diabetes that can otherwise undermine the body's defenses against COVID-19.

Things that can weaken the immune system

-- Medical conditions.

-- Medications.

-- Smoking.

-- Stress.

-- Sleep problems.

-- Isolation.

-- Poor diet.

-- Sedentary lifestyle.