Free Radicals: How Do They Affect Our Bodies?

Written by Ahmed Zayed | Last updated on August 4, 2023

You are probably aware that drinking alcohol, smoking, and being exposed to pollution can contribute to diseases and aging. However, have you ever asked yourself why?

In part, the answer can be explained by free radicals.

What Are Free Radicals?

Free radicals are unstable atoms that can damage the cells in our body. They are oxygen-containing molecules with an unpaired electron. That single electron enables them to interact freely with other molecules, which is not often good.

illustration of a free radical

Those molecules can trigger a chain of chemical reactions in our body known as oxidation. That causes harm and signs of aging. 

They are naturally produced in the body during our day-to-day life—when we metabolize food—but they’re also produced by external sources [1].

Some of the external sources of free radicals include:

  • Processed meats
  • Pesticides
  • Cigarette smoke
  • Alcohol
  • Air pollution

Can Free Radicals Damage Our Body?

A free radical overload sets off a process known as oxidative stress. Oxidation is composed of chemical reactions damaging our cells. That is where antioxidants enter.

Typically, our body can combat that stress through its antioxidation defenses. However, when the antioxidant-producing capacity becomes overpowered by free radicals, damage can happen as our body cannot keep up [2].

For instance, sun exposure. Have you ever thought about how sunlight causes free radicals in the body?

woman under the sun

Excessive UV radiation from the sun could overwhelm the system, triggering these unstable molecules and provoking oxidative stress (photoaging).

That’s another reason why regular sunscreen use is essential.

But it doesn’t stop there. Free radicals generate more unstable atoms when they steal electrons from numerous atoms. In turn, it creates a harmful chain reaction.

Every time those free radicals attack vital molecules in the cell, it results in big-scale cell damage and subsequent disease.  

Sources of Free Radicals

Free radical theories of aging and disease might help explain why others age slower than others.

Even though these are produced naturally in our bodies, lifestyle factors can also quicken their production. Those include [3]:

  • fried foods
  • alcohol
  • smoking
  • exposure to toxic chemicals, like air pollution and pesticides

Those lifestyle factors have been associated with diseases like cancer and cardiovascular illness. Therefore, oxidative stress might be why exposure to those substances causes illness. 

Types of Free Radicals

You will find various types of free radicals. But remember that the reactive oxygen species are the most critical in humans [4].

Oxygen free radicals include:

  • Hydroxyl radicals - These are produced during normal cellular metabolism, causing damage to DNA, proteins, and lipids. They’re the most reactive and damaging free radicals in our bodies.
  • Lipid peroxides - These are lipid oxidation products that can harm DNA and cell membranes. They are caught up in the development of cancer, atherosclerosis, and other chronic diseases.
  • Reactive oxygen species (ROS) – Our body naturally produced these as a byproduct of cellular metabolism. However, too much product can cause inflammation, oxidative stress, and damage to cell membranes, lipids, and proteins. It can also contribute to the development of cardiovascular disease, chronic diseases such as cancer, and neurodegenerative disorders.
  • Nitric oxide (NO) - This is a signaling molecule in the body regulating blood flow, immune function, and neurotransmission. Nevertheless, too much product can result in oxidative stress and inflammation. It damages tissues and contributes to the development of chronic diseases.

What Are Antioxidants?

Antioxidants are molecules that are responsible for fighting free radicals in our bodies. Did you know our body has antioxidant defenses to keep free radicals at bay?

fruits that contain antioxidants

Nonetheless, these molecules are also found in our foods, particularly vegetables, fruits, and other plant-based, whole foods. Some vitamins like C and E are good antioxidants, too.

Antioxidants can be grouped as either fat-soluble or water-soluble. The latter perform their actions in the fluid and outside cells. On the other hand, the former act mainly in the cell membranes.

Below are some of the important antioxidants [5]:

  • Flavonoids are a group of plant antioxidants with numerous health benefits [5].
  • Vitamin C is a water-soluble antioxidant that is also a vital dietary nutrient.
  • Vitamin E is a fat-soluble antioxidant that protects cell membranes against oxidative damage.

Numerous drinks and foods are great sources of antioxidants, such as green tea and berries.

The Role of Free Radicals in Aging

As we age, our body's ability to produce antioxidants decreases while the production of free radicals increases [6]. Free radicals are molecules that can cause damage to our cells, leading to oxidative stress.

This can result in an imbalance between free radicals and antioxidants in the body.

Oxidative stress can have a significant impact on our health, particularly in terms of age-related diseases. Research has shown that oxidative stress plays a role in developing conditions such as Alzheimer's disease, Parkinson's disease, arthritis, and cardiovascular disease.

Free radicals can damage DNA, proteins, and other essential molecules when they attack healthy cells. This damage can lead to mutations in the DNA, which can increase the risk of developing cancer.

Additionally, oxidative stress can also contribute to chronic inflammation, exacerbating various health problems.

How to Measure Free Radicals

Measuring free radicals in our body can be difficult because of their short lifespan and highly reactive nature. Nonetheless, various methods have been created to evaluate our bodies’ levels of free radicals.

1. Various biomarkers of oxidative stress have been determined. This includes F2-isoprostanes, protein carbonyls, and oxidized low-density lipoprotein [ox-LDL]. These procedures can be measured through a urine or blood sample [7]. 

2. You can also measure the free radicals in our body through an oxygen radical absorbance capacity [ORAC] assay, even though it indirectly assesses the free radical levels. You can measure antioxidant capacity in biological samples [8].

3. Another common method used is measuring oxidative damage levels to cellular components. For instance, you can measure the levels of lipid peroxidation products such as malondialdehyde [MDA] and 4-hydroxy-2-nominal [HNE] in tissue or blood samples as markers of oxidative stress [9].

How to Reduce Free Radicals in Our Body

The reality is that we can’t prevent free radicals. However, we can limit our exposure to some unnecessary free radicals.

There are two ways to do that. One is to control how many of them we let in, and the other is to take enough antioxidants to keep them from taking center stage.

1. Limit exposure to free radicals.

Researchers recommend a few ways we can protect ourselves from an abundance of free radicals [10]:

  • Manage stress
  • Limit time in the sun [and use sunscreen properly]
  • Limit alcohol intake
  • Don’t smoke
  • Avoid pollution
  • Get a moderate amount of exercise

2. Consume foods rich in antioxidants.

Remember that antioxidants are the key to keeping free radicals from damaging your healthy cells. Our body naturally produces some of them, but an antioxidant-rich diet can help, too.

Getting them from our diet has been proven to lessen our risk of damage and oxidative stress. You can try these vitamin-rich foods that are also rich in antioxidants.

Zinc – Fortified cereals, cashews, lentils, chickpeas, pumpkin seeds, sesame seeds, oysters, shrimps, poultry, beef

Selenium – Tuna, salmon, eggs, brown rice, onions, shellfish, poultry, and beef [limit to no more than 1-2 servings per week]

Beta carotene – Mangos, carrots, cantaloupe, apricots, pink grapefruit, bell peppers, asparagus, beets, squash, tomatoes, sweet potatoes, tangerine, and watermelon

Vitamin E – Leafy greens, red pepper, peanuts, legumes, oatmeal, sunflower seeds, avocado, and almonds

Vitamin C – Brussels sprouts, broccoli, tomatoes, citrus fruits, bell peppers, sweet potatoes, strawberries, kale, grapefruit, cauliflower, and blueberries

Free Radical Scavenging Supplements

Again, we cannot avoid free radicals, part of our body’s normal processes. We can lessen their impact on our appearance and health with free radical scavenging supplements.

A free radical scavenging supplement may also be known as an antioxidant.

It refers to any molecule that is stable enough to donate an electron to a free radical in our body, neutralizing it or minimizing its capacity to do damage.

Fortunately, nature offers plenty of substances and nutrients to fill that role.


This polyphenol is naturally found in the skin of red grapes, berries, and other plants. Research has found that it can help support healthy cardiovascular function.

Alpha lipoic acid

ALA has often been deemed the “universal free radical scavenger” due to its unique capability to function in fat and water. Alpha lipoic acid also helps our body to recycle vitamins C and E, extending their antioxidant activities.


Some minerals, such as zinc, copper, and selenium, also have free radical scavenging features. One of the most popular is the trace mineral selenium. Did you know that this is an essential nutrient for humans?

It protects us from free radical damage thanks to its role as a cofactor for the antioxidant enzyme glutathione peroxidase.


Vitamins A, C, and E are also free radical scavengers protecting us from free radical damage. A good example is vitamin C, a hydrophilic radical scavenger seeking out free radicals in water-based environments.

On the other hand, vitamin E is lipophilic, seeking and neutralizing free radicals in fatty environments.

Antioxidant Foods and Supplements: Do They Actually Work?

You can find multiple dietary supplements claiming to be antioxidants, made of plant extracts or nutrients that have demonstrated antioxidant activity in a lab.

Although consuming foods rich in antioxidants seems advantageous, these supplements do not provide the same benefits, except in rare situations.

One of those cases is the combination of zeaxanthin, lutein, and other nutrients, which may slow the development of macular degeneration, which is the top cause of blindness in older people [11].

Even though antioxidant supplements are normally deemed safe, some research recommends that specific antioxidant supplements can do more harm than good. That isn’t what you like if you try to get or stay healthy [12].

Instead of spending money on costly dietary supplements, you are better off getting more veggies, fruits, and other healthy foods.

Free Radical Theory of Aging

The free radical theory of aging is relatively new, but many studies support it. For instance, studies on rats showed substantial increases in free radicals as the rats aged.

Such changes matched up with age-related declines in health [13].

Over time, researchers have modified the free radical theory of aging to concentrate on the mitochondria [14]. These are small organelles in cells that process nutrients to power our cells.

A study on rats also recommends that free radicals generated in the mitochondria damage the substances that the cells require to work properly.

That damage causes mutations that create more free radicals, thus increasing the process of damage to the cell.

The theory also discusses aging since it accelerates over time. The slow but increasingly fast accumulation of free radicals explains why even healthy bodies age and deteriorate over time.

How Do You Test Antioxidant Status?

The assessment of an individual’s oxidative stress-related disease risk can be facilitated by measuring their antioxidant status. Two of the commonly used methods are the following:

Serum antioxidant capacity

Serum antioxidant capacity measures the ability of the antioxidants in the blood to scavenge free radicals and protect against oxidative stress.

 One study found that a higher serum antioxidant capacity was associated with a lower risk of developing cardiovascular disease [15].

Antioxidant capacity assays

This antioxidant tests the ability of a substance to scavenge free radicals and prevent oxidative damage. Examples of antioxidant capacity assays include the oxygen radical absorbance capacity [ORAC] assay and the ferric reducing antioxidant power [FRAP] assay.

One study evaluated the antioxidant capacity of different teas using the ORAC assay and found that green and white teas had the highest antioxidant capacity. In contrast, black tea had the lowest [16].

Future Of Free Radical Research

New areas of study and potential treatments are constantly emerging in the exciting and dynamic field of free radical research. Here are a few instances:


New research suggests that free radicals can alter gene expression without changing the DNA sequence by causing epigenetic changes. This opens up a new field of inquiry into how it might affect conditions like cancer and Alzheimer’s.

The mitochondria’s role

Cell organelles called mitochondria produce energy. Free radicals can harm mitochondria, resulting in cellular disease and dysfunction. Researchers are looking into various options to prevent mitochondrial deterioration and enhance mitochondrial function [17].


The study of nutrigenomics focuses on how diet influences gene expression. Antioxidant-rich diets are being researched for their potential to lower oxidative stress and prevent disease [18].

New treatments

Antioxidants, compounds that target the mitochondria, and gene therapy are some of the new treatments being investigated by researchers for diseases linked to oxidative stress [19].

Free radical and oxidative stress research, along with other research areas, are showing promise for creating fresh treatments and disease prevention strategies.

Frequently Asked Questions 

Do antioxidant supplements fight free radicals?

Dietary intake of antioxidants is vital for optimal health. However, more isn’t always better.

Too much intake of isolated antioxidants could have detrimental impacts and may promote rather than stop oxidative damage. It is called the “antioxidant paradox” [20, 21].

Some studies even prove that high doses of antioxidants increase the risk of death [22].  


Indeed, a massive difference exists between a human and a fruit fly or a rat. Therefore, more work should be done on the role of free radicals and aging.

Researchers hope that later on, we can take a pill that fights free radicals.

But until then, we are stuck staying healthy and combating free radicals the old-fashioned way: no cigarettes and alcohol, a healthy diet, and regular exercise.


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[12] Harvard T.H. Chan School of Public Health. Antioxidants. 2020.

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[18] Borel, P., & Desmarchelier, C. [2016]. Genetic Variations Involved in Vitamin E Status. International journal of molecular sciences, 17[12], 2094.

[19] Skulachev, V. P., Holtze, S., Vyssokikh, M. Y., Bakeeva, L. E., Skulachev, M. V., Markov, A. V., Hildebrandt, T. B., & Sadovnichii, V. A. [2017]. Neoteny, prolongation of youth: From naked mole rats to "naked apes" [humans]. Physiological Reviews, 97[2], 699-720.

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[21] Henkel, R., Sandhu, I. S., & Agarwal, A. [2019]. The excessive use of antioxidant therapy: A possible cause of male infertility? Andrologia, 51[1], e13162.

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About the author 

Dr Ahmed Zayed is a medical resident specializing in plastic surgery with years of experience in the field. He is also a writer for top-rated websites including Washington Post, Chicago Tribune, ConsumerHealthDigest, and Huffington Post

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