7 Fascinating Things Nobody Ever Taught You About Your Immune System

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The immune system is one of the most important systems in your body. It's always working for you, doing its best to make sure you don't get sick or to get you better when you are sick. When the immune system malfunctions, a lot can go awry, so it's essential to take care of yours. And when it's functioning properly, it does some pretty cool things.

"The essential task of the immune system is to maintain a balance between reaction and tolerance," Kiran Krishnan, research microbiologist and scientific advisor for ProBioGen, tells Bustle. "You want your immune system to react to the pathogens that can make you sick, while letting the beneficial bacteria living in your gut go about their business. The regulatory component of your immune system (the Treg cells that stop unwanted immune response like allergies) are controlled in large part by the gut microbiome and the gut-associated immune system. Having a diverse microbiome and alleviating leaky gut are foundational to supporting a healthy immune system and, in turn, all-around wellbeing."

The immune system does amazing things to keep you healthy, and it's surprisingly malleable. Here are some fascinating things to know about your immune system, according to experts.

1. Most Of It Is In Your Gut

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One reason gut health is so important is that it determines how well we can fight off disease. "The tissue in your gut wall contains 70 to 80 percent of the immune cells in your entire body," nutritionist Lisa Richards, creator of the Candida Diet, tells Bustle. "When your intestinal membrane is inflamed or your gut flora become imbalanced, it can have a real, immediate effect on your immune system."

To improve your gut health, Richards recommends reducing added sugars, processed foods, and inflammatory foods, eating high-fiber vegetables and fermented foods, and taking probiotics. You may also see benefits to your digestion, skin, and mood.

2. Your Childhood Diet Affects It

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When children are exposed to foods at a young age, they develop a tolerance, Wendy Sue Swanson, MD, MBE, pediatrician and chief of digital innovation at Seattle Children’s Hospital, tells Bustle. So, eating things like peanuts, eggs, and fish at a young age can prevent people from developing allergies.

"The tummy is an essential part of how babies become tolerant to foods, and feeding potential allergens is key to that," Dr. Swanson says. "Food allergies doubled each decade during a time when it was thought that you should delay introducing some foods like peanuts during infancy and toddlerhood. The delayed introduction that was recommended by pediatricians likely contributed to the development of more food allergies."

3. Childhood Stress Affects It

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"Childhood stress has been shown to cause prolonged immune changes in children," Caitlin Thompson, neurobiology researcher and founder of Entheozen, tells Bustle. "Stress and trauma shut down the parasympathetic response and activate the sympathetic response, suppressing the immune system, restorative processes, and digestion. A stress response is an energetically expensive state to be in and will utilize resources in the body that are saved for emergency situations, such as running from a predator, shutting down processes that are less dire for short term survival."

One study in Psychosomatic Medicine, for example, found that people who experienced trauma in their childhoods were more likely to be hospitalized with autoimmune diseases. Another study in JAMA found that stress-related disorders were linked to higher risk of autoimmune disease.

4. Your Attitude Affects It

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The good news is, you can counteract the effects past stress may have had on your immune system by adopting a positive attitude now. One Carnegie Mellon study found that people who described themselves as happy, lively, or calm were less likely to get sick when exposed to a cold virus.

"Some research has linked positive thinking and optimism to improved immune functioning," Nesochi Okeke-Igbokwe, MD, physician and health expert, tells Bustle. "It is believed that positivity may have a protective effect against stressful stimuli that negatively impact one's immune system."

5. It Changes As You Get Older

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One important part of the immune system is the thymus, a gland at the top of your chest between your lungs, says Dr. Okeke-Igbokwe. However, this organ changes drastically throughout your life.

"The gland has very high activity in producing T cells during puberty, but it starts to rapidly decrease in size post-puberty, during which T cell production really slows down," Dr. Okeke-Igbokwe explains. "Adipose tissue replaces the gland in adulthood, and it then loses most of its functionality." We likely rely on it less as adults, as removing it has less of an impact.

6. It Changes When You Get Pregnant

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Another thing that changes your immune system is pregnancy. "When a woman is pregnant, her immune system and immune response are weakened," Dr. Okeke-Igbokwe says.

These changes make you more likely to get an illness, like the common cold or flu, when you're pregnant, so it's extra important to strengthen your immune system and keep germs at bay.

7. It Can Affect Your Brain

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Since most of the immune system is in the gut, it's also part of the gut-brain axis — the connection between the stomach and the brain.

"Signals run along axes from the gut to other parts of our bodies via neurons, hormones, and perhaps most importantly, via the immune system," Krishnan explains. "The gut is able to alter the brain chemistry via neuronal pathways and through messengers of the immune system called cytokines — and these messengers depend on the state of the gut microbiota."

To give your immune system a boost, you can eat probiotic and prebiotic foods, get enough magnesium, vitamin D, and zync in your diet, and get lots of sleep. It will thank you in turn.