What is Oxidative Stress, and Why is it Important?

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What is Oxidative Stress, and Why is it Important?

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Oxidative stress is “a disturbance in the balance between the production of free radicals and antioxidant defenses, which may lead to tissue injury”.

Our bodies are host to hundreds of cellular reactions. Free radicals are the by-products of these cellular reactions. When the imbalance tilts toward high free radicals, oxidative stress is the result.

So what exactly are free radicals, and how are they produced? Free radicals are atoms or molecules with odd numbers of (unpaired) electrons. The odd number of electrons increases the reactivity and instability of an atom. 

Free radicals want to acquire electrons to become more stable, so they react with other molecules to steal electrons from them and, in turn, make other molecules unstable too, starting a chain reaction. 

If antioxidants don’t interfere in this process, an increase in free radical production leads to oxidative stress, causing tissue damage. 

Free radicals can be reactive oxygen species (ROS) as well as reactive nitrogen species (RNS). Examples of ROS include hydrogen peroxide (H2O2) and the superoxide radical anion (O2•−). 

A low to mild levels of free radicals are good for health because they fight infections, but high levels of radicals are a cause of many chronic diseases (1,2).

Diseases caused by oxidative stress include (3):

  • DNA damage and cell death
  • Aging
  • Neurological disorders (depression, cognitive impairment, dementia, Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and multiple sclerosis)
  • Cardiovascular dysfunction (atherosclerosis, ischemia, hypertension, cardiomyopathy, cardiac hypertrophy, and congestive heart failure)
  • Cancer  
  • Diabetes 
  • Kidney diseases
  • Sarcopenia and frailty

What Factors Increase the Risk of Oxidative Stress?

Certain external factors exacerbate the production of free radicals, including ROS and RNS. Reducing their exposure reduces oxidative stress (4).

The examples include:

  • Ionization radiation
  • Cigarette smoke 
  • Heavy metals
  • Drugs
  • Pollutants
  • Pesticides

The factors mentioned are the most important contributors to oxidative stress. Eliminating these factors provides benefits in reducing oxidative stress. 

How to Fight Oxidative Stress in a Healthy Way

Reducing oxidative stress by antioxidants presents a major strategy to fight excessive oxidative stress and is significant for chronic disease prevention.

There are two major strategies to fight oxidative stress. 

  1. Antioxidant-rich food
  2. Lifestyle changes

1) Antioxidant-rich food

Natural antioxidants are present in many of the foods available to us. Increasing the consumption of healthy foods high in antioxidants is the most important strategy for reducing oxidative stress. 

Examples of antioxidants are: 

  • Vitamins
  • Minerals
  • Polyphenols
  • Other bioactive compounds

Antioxidant vitamins

Vitamin A: Extensive studies have been conducted to investigate the antioxidant properties of vitamin A and carotenoids. Vitamin A and its variants are part of many complex pathways to impart antioxidant function (5).

Vitamin A cannot be produced in the body, so it must be obtained from food. Food sources of vitamin A include:

  • Organ meat (liver, kidney)
  • Fish
  • Eggs
  • Milk
  • Cheese
  • Butter
  • Carrots
  • Sweet potatoes
  • Tomatoes

Recommended dietary allowance (RDA) per day for men is 900 micrograms and for is women is 700 micrograms (6).

Vitamin C: Vitamin C (ascorbic acid) has many important functions in the body, but it is also a vital antioxidant. Vitamin C supplements are used for the prevention of diabetes, stroke, common cold, cataracts, atherosclerosis, etc. (7).

Food sources of vitamin C include:

  • Citrus fruits
  • Green peppers
  • Red peppers
  • Strawberries
  • Tomatoes
  • Broccoli
  • Leafy vegetables

The recommended daily allowance for vitamin C is 90 mg for adult men and 75 mg for adult women (8).

Vitamin E: Vitamin E is the most studied vitamin for its antioxidant function. It has many variants. Alpha-tocopherol is studied in several diseases, including cardiovascular and brain diseases (9).

Seeds has magnesium

Major food sources of vitamin E are:

  • Sunflower seeds
  • Almonds
  • Hazelnuts
  • Peanuts
  • Spinach 
  • Broccoli
  • Kiwifruit 

Recommended dietary allowances of vitamin E for adult men and women is 15 mg.

Although vitamins induce proper antioxidant function, excess amounts can cause oxidative stress. Therefore, one should consume in moderate amounts. 

Antioxidant Minerals

Zinc is one of the most studied antioxidant minerals. Zinc deficiency results in various growth and development problems. Its deficiency increases oxidative stress, and supplementation improves antioxidant function (10).

Major sources of zinc are (11):

  • Oysters
  • Beef 
  • Chicken 
  • Pork 
  • Pumpkin seeds
  • Yogurt
  • Milk 
  • Cheese

Recommended dietary allowances of zinc for adult men is 11 mg and for adult women is 8 mg.

READ: How zinc plays an essential role in human health

Selenium is a trace element whose small quantities are required for proper health. Selenium is part of many enzymes called selenoenzymes. The activity of selenoenzymes is required for lowering oxidative stress. The deficiency of selenium leads to many diseases (12).

Vegetables and fruits are poor sources of selenium. Major food sources of selenium include (13):

  • Brazil nuts
  • Beef liver
  • Tuna
  • Turkey
  • Seafood
  • Eggs
  • Turkey 

Recommended dietary allowances of selenium for adult men and women is 55 micrograms.


blueberries anti-inflammatory anti-oxidant

Polyphenols are plant-based natural antioxidants. More than 8000 polyphenols have been identified in plants.

Among polyphenols, flavonoids are the most studied compounds. Other plant polyphenols are stilbenes and lignans. 

They can be found in vegetables, fruits, cereals, chocolate, and beverages. 

Apple, grapes, berries, cherries, and pears contain between 200-300 mg polyphenols per 100 g of fresh weight. 

A typical glass of red wine and green tea contains about 100 mg of polyphenols (14).

Red wine is rich in polyphenols such as resveratrol, catechin, epicatechin, quercetin, and anthocyanin (15).

Green tea is also a popular source of polyphenols. EGCG is the most studied polyphenol and a potent antioxidant (16).

Most studied vegetables and fruits for antioxidant polyphenolic compounds include the following (17).

  • Berries
  • Cherries
  • Pomegranate
  • Orange 
  • Lemon
  • Papaya
  • Apple 
  • Chili pepper
  • Kale
  • Cabbage
  • Spinach
  • Broccoli
  • Tomato 
  • Garlic
  • Ginger

Other bioactive antioxidants


Coenzyme CoQ10 is an important fat-soluble antioxidant. The reduced form of CoQ10 called ubiquinol performs the antioxidant function. CoQ10 performs a significant function of activating other antioxidant vitamins C and E. 

READ: What are other benefits of CoQ10 in human health


oily fish is source of fish oil and omega3

Omega-3 anti-inflammation function is studied extensively, in addition to some studies showing its antioxidant function. Antioxidant and anti-inflammation functions are closely related. Omega-3s are a special kind of fatty acid that becomes part of the cell membrane, from where they promote ant-inflammation. 

READ: What is the recommended daily intake of omega-3 


Curcumin is a natural antioxidant found in turmeric. It is an important dietary herb in South Asia. Turmeric consumption can reduce oxidative stress and inflammation. 

READ: What is turmeric and what are other health benefits 


Probiotics are living microorganisms that add benefits to the health of humans. In recent years, several studies have shown that probiotics are important for reducing oxidative stress (18).


Melatonin is a naturally occurring bioactive compound in our bodies. It regulates sleep (circadian rhythm) and enhances the immune system. It is also a potent antioxidant and reduces oxidative stress (19).

Foods high in melatonin include: 

  • Fish
  • Eggs
  • Mushrooms
  • Grapes
  • Tart cherries
  • Tomatoes
  • Pistachio
  • Walnuts
  • Cereals

2) Lifestyle changes  

Lifestyles change presents the second way to reduce oxidative stress. 

Exercise regularly

Regular exercise is significant to reduce oxidative stress. Research shows that exercise increases the activity of antioxidant enzymes.

However, intense and strenuous exercise increases inflammation and oxidative stress. Moderate exercise and an active lifestyle is the best strategy to decrease oxidative stress (20).

Quit smoking

Cigarette smoking increases oxidative stress in the human body. The effect of cigarette smoking on oxidative stress is so detrimental that an increased daily intake of antioxidants is recommended. For example, for smokers, 35 mg more daily vitamin C is recommended compared to non-smokers (21).

Quitting cigarette smoke provides an important way to reduce oxidative stress.

Limit alcohol intake

Although wine and other alcoholic beverages have anti-oxidant polyphenols, use of high alcohol consumption and hard liquor may outweigh the benefits of taking polyphenols of alcohol (22).

Limiting the intake of alcohol may decrease oxidative stress.

Avoid fast food

Fast food is high in saturated fats and simple sugars. Dietary intake of antioxidants is a powerful strategy to reduce oxidative stress. Fast food lacks antioxidants (23).

Replacing fast food with a high vegetable and fruits diet is beneficial for reducing oxidative stress.

Intermittent fasting

Short-term fasting reduces oxidative stress. Intermittent fasting has been studied extensively. It has several health benefits and may present a good strategy to reduce oxidative stress (24).

The Gist

Oxidative in low to moderate levels is good, but high oxidative stress leads to many chronic diseases. 

Oxidative stress increases with an unhealthy diet and lifestyle, in addition to environmental factors. 

Adding antioxidant foods provides an excellent strategy to fight oxidative stress. 

Including exercise, avoiding cigarettes, and limiting alcohol and fast food in your lifestyle will reduce oxidative stress.  

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