Skip to content

Surprising Side Effects Apples Have On Your Immune System, Says Science

It's shocking how one small apple can affect your body!
FACT CHECKED BY Meaghan Cameron

When it comes to convenient and nourishing snacks, you can't beat an apple. It's a satiating option you can grab on your way out the door to run errands, or throw into your lunch bag for work. Fortunately, apples are also available year-round in the U.S. and loaded with vitamins, minerals, fiber, and antioxidants—all the nutrients your body needs to fend off viruses and other infections and ailments.

So, does an apple a day really keep the doctor away? The jury is still out on that one, but 2015 research showed that a fraction of adults who live by this healthy habit do seem to require fewer prescription medications.

Whether you prefer to nosh on this fruit whole, slice them up with almond butter, or toss them into your salads, you'll want to know some of the following side effects apples can have on your immune system. Plus, try one of our 22 Meals to Melt Belly Fat in 2022.

The quercetin helps to keep inflammation in check.

Apples are a rich source of phytochemicals—like quercetin, which is known for its antioxidant and anti-inflammatory effects that help with regulating immune responses.

Here's the gist of how it works. Free radicals not only damage your cells but also activate genes that trigger an increased inflammatory response. Chronic inflammation is linked to many serious diseases and health problems, but fortunately, studies have shown that quercetin can reduce markers of inflammation.

Red apples, in particular, seem to be high in this flavonoid. Also, don't peel your apples or you'll miss out on this health benefit—because quercetin is exclusively found in the skin.

Here's This One Trick Will Make Your Apples Stay Fresh for Longer.

The flavonoids help to regulate the immune system.

bowl of apples

Quercetin isn't the only antioxidant that apples contain. They also boast a number of other flavonoids, like catechin, epicatechin, procyanidin, phloridzin, coumaric acid, chlorogenic acid, and gallic acid, which have inflammatory and immune system benefits. In fact, when compared to other popular fruits, apples had the second-highest level of antioxidant activity and the highest proportion of free phenolics.

Research has demonstrated that these types of phytochemicals regulate both inflammatory and immune responses, while also protecting the body from oxidative stress.

Keep in mind, though, that the flavonoids in apples are largely concentrated in the skin, and tend to be higher in darker red-colored varieties.

Get even more healthy tips straight to your inbox by signing up for our newsletter!

The pectin supports your gut health.

Did you know that a large portion of your immune system lies in your GI tract? That means that keeping your microbiome healthy and balanced is key to making sure your body is prepared to fight off infections. Apples can help to support gut health because they provide a specific type of soluble fiber called pectin. One 2010 study found that when women consumed two apples a day, they increased the good bacteria in their guts after just two weeks.

According to a 2019 study published in Frontiers of Microbiology, a single apple contains nearly 100 million bacteria cells. Note that the study also found that organic apples seem to have an advantage over conventionally grown apples, as they offer a more diverse array of bacteria.

The vitamin C fuels processes that protect you from infections.

apples peanut butter

It's no secret that vitamin C is one of your body's best defenses when it comes to warding off pesky colds and other illnesses. What you may not realize, however, is that it plays many different roles in boosting your immune system.

Studies have shown that by simply consuming more vitamin C, you can increase the levels of antioxidants in your blood by a whopping 30%—and in turn, this can help your body's defenses to keep inflammation at bay.

A 2017 review published in the journal Nutrients found that vitamin C also strengthens the epithelial barrier against pathogens and protects your cells against environmental oxidative stress.

One large apple contains around 10.3 mg of vitamin C, which may not seem like much, but it provides 11.4% of your RDA. Plus, research has also revealed that the antioxidant activity in one serving's worth of apples (100 grams) is equivalent to a whopping 1,500 milligrams of vitamin C.

Fun fact: A raw apple with the skin on packs up to 115% more vitamin C than a peeled one.

The soluble fiber converts immune cells to become anti-inflammatory.

woman apple shopping in grocery store

If there's one thing apples have going for them, it's fiber. One medium-sized apple offers 4.4 grams toward your RDA of 25 grams. So, what does this have to do with your immune system? A 2010 University of Illinois study discovered that the soluble fiber found in apples changes the "personality" of immune cells from pro-inflammatory to anti-inflammatory. In fact, mice who were fed soluble fiber only got half as sick as the other group, and recovered 50% sooner, after scientists induced illness in all of them. Authors of the study claim that the reason for this effect is that soluble fiber triggers an increase in the production of an anti-inflammatory protein called interleukin-4.


Rebecca Strong
Rebecca Strong is a Boston-based freelance health/wellness, lifestyle, and travel writer. Read more about Rebecca
Filed Under