As the weather gets colder, more Americans will start getting sick with the flu or Covid-19. Here are four ways health experts say you can help improve your immune system to better protect against getting sick, Hannah Seo reports for the New York Times' "Well."

4 ways to improve your immune system

1. Be active

According to David Nieman, a professor of biology at Appalachian State University, exercise is an excellent way to improve your health and fight against disease.

In a study published in 2011, Nieman and colleagues looked at more than 1,000 adults in North Carolina for three months in 2008 and logged their lifestyle habits, including what they ate, their exposure to stressful events, their exercise habits, and how often they were sick with different upper respiratory tract infections.

"The No. 1 factor that emerged was physical activity," Nieman said. Study participants who exercised at least five days a week were 43% less likely to develop an upper respiratory tract infection than those who exercised less than one day a week. Even participants who did just 20 minutes or more of moderate exercise at least once a week were less likely to get sick than those who did none, the study found.

According to Nieman, exercise stimulates the immune cells to "patrol the body" looking for cells infected by a virus so they can be eliminated. Even a small amount of exercise, like walking, dancing, or "vigorous yard work" can improve your health, he added.

However, Nieman cautioned that too much exercise can increase your risk of infection. If you're feeling sick or constantly tired, or if workouts that used to be easy are now hard, it might be a signal you need to scale back, Nieman said.

2. Get enough rest

According to Kathi Heffner, a professor of nursing, medicine, and psychiatry at the University of Rochester Medical Center, research has found not getting enough sleep, or enough good quality sleep, can reduce your body's ability to fight off infection. Not everyone requires the same amount of sleep, but general guidelines recommend six to eight hours of sleep each night for adults, Heffner said.

Getting enough sleep can also help with stress, Heffner added. When someone suffers from chronic stress, their body's response to vaccines and infections can be reduced and inflammation can be increased, "all of which can increase our susceptibility to infection as well as other kinds of chronic diseases," Heffner said.

3. Eat healthy

One of the most important lifestyle choices you make that can affect your immune system health is your diet, Nieman said.

He recommends a diet of different brightly colored fruits and vegetables—including berries, citrus fruits, red cabbage, and kale—as they are great sources of flavonoids, which can help the body fight off inflammation and illness. Tea, coffee, dark chocolate, and certain grains like buckwheat are also good sources of flavonoids.

In Nieman's study, he found that participants who ate at least three servings of fruit each day had fewer respiratory tract infections than those who ate less fruit.

Other research has also found the being exposed to cigarette smoke and drinking alcohol in excess—which is more than two drinks a day for men and more than one drink a day for women—can harm your immune system. Keeping your alcohol consumption within dietary guidelines or quitting smoking could reduce your risk of infections, according to Helen Chu, an epidemiologist and infectious disease physician at the University of Washington School of Public Health.

4. Continue pandemic precautions

According to Chu, "the most important thing that people can do right now is to get both their up-to-date Covid booster shots and their flu vaccines as soon as possible," since both flu and Covid-19 cases will likely increase this fall and winter.

In addition, continuing to wear a mask in public indoor spaces will protect you not just against the coronavirus but against other viruses as well, especially if you have a weaker immune system, Seo reports. Chu added that using rapid Covid-19 tests before gatherings or when you have Covid-19 symptoms can help minimize infection risk.

"One of the things we've learned through this pandemic is just how important hygiene is," Heffner said. "Washing hands, keeping your distance when you have a cold—those kinds of things are highly effective for keeping people healthy."

Chu added that good hygiene also includes staying home when you have symptoms of any kind of infection. "People tend to try to power through, even if they're sick," she said. "They want to continue to do their job, to continue to go to school, to continue to do what they were doing before." But doing so will just increase exposure risk and transmission, Chu said, so if you're sick, you should stay home and rest instead. (Seo, "Well," New York Times, 10/14)