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An antioxidant is a substance that protects the cells in your body from damage caused by free radicals.
Free radicals have an unshared electron that causes them to be highly energetic and quick to react. They are created as a by-product when your metabolism converts food to energy or after exercise occurs. Environmental factors such as smoking and pollution can produce free radicals as well.
An excessive number of free radicals can lead to certain diseases or comorbidities such as cardiovascular disease, cancer, or vision defects. Antioxidants share electrons with free radicals to decrease their reactivity and therefore decrease the damage caused to your cells.
Certain vitamins, minerals, and phytochemicals in the food you consume act as antioxidants. The antioxidants found most abundantly in food are vitamin E, vitamin C, selenium, and beta-carotene.
More research needs to be done to determine how each antioxidant plays a role in preventing certain diseases. Therefore, it is best not to make association statements due to the lack of causation studies.
Antioxidant Food Sources
Here are the best food sources of antioxidants that you can include in your daily meals.
1. Vitamin E
Vitamin E functions as an antioxidant and an anti-inflammatory agent. Some sources of vitamin E include whole grains, seed/nuts, peanut butter, vegetable oils, green leafy vegetables, and fortified cereals.
The recommended dietary allowance (RDA) for an adult is 15 mg. (1) However, the average American does not meet the RDA. The RDA for vitamin E can be met with 2 oz of sunflower seeds, 3 oz of almonds, or 4 cups of spinach.
2. Vitamin C
Vitamin C functions as an antioxidant and a cofactor in collagen synthesis. Some sources of vitamin C include citrus fruits, berries, tomatoes, and broccoli. The RDA for an adult is 90 mg for males and 75 mg for females. (2) The average American typically meets the RDA.
Selenium is a trace element that functions as an antioxidant. Some sources of selenium include Brazil nuts, seafood, and organ meats. The RDA for an adult is 55 mcg. (4) The average American typically meets the RDA.
The RDA for selenium can be met with 1 oz of Brazil nuts, 3 oz of yellowfin tuna, or 5 oz of turkey.
Beta-carotene is a phytochemical (“plant” chemical) that functions as an antioxidant and precursor to vitamin A. Some sources of beta-carotene include sweet potatoes, spinach, carrots, broccoli, and tomatoes.
There is no RDA for beta-carotene and no measurement to determine the amount of this phytochemical.
If you are unable to include antioxidant-rich foods in your diet, supplementation may be a good alternative to meet your personal micronutrient needs. However, supplementation may not be as effective in protecting against certain diseases.
It is important to note the tolerable upper limit (UL) for each antioxidant because this level determines the dosage deemed safe for consumption. Exceeding this amount may lead to adverse health effects. (5)
1. Vitamin E
The tolerable UL for vitamin E is 1,000 mg/day for an adult. (6) High doses of vitamin E that exceed the UL may result in excessive bleeding. It is advised to be cautious while on blood-thinning medication, such as warfarin, due to the increased risk of bleeding.
Also, chronic high doses of vitamin E supplementation may lead to an increased risk of prostate cancer. No adverse health effects have been found from consuming food sources of vitamin E.
2. Vitamin C
The tolerable UL for vitamin C is 2,000 mg/day for an adult. (7) High doses of vitamin C may cause gastrointestinal discomforts such as diarrhea or cramps. Otherwise, this vitamin is relatively safe at higher levels. It is advised to be cautious of vitamin C’s role in iron absorption, as it may lead to excessive iron levels and result in cell damage.
Vitamin C increases iron absorption; therefore, it is recommended to discuss vitamin C and iron supplementation with your doctor to understand the correct and safe dosing for your individual health.
The tolerable UL for selenium is 400 mcg/day for an adult. (8) Chronic high doses of selenium may lead to brittle hair and nails and can sometimes result in hair loss.
As mentioned above, Brazil nuts are an excellent source of selenium. However, 1 oz of Brazil nuts is ~500 mcg. Habitual consumption of Brazil nuts may cause these adverse effects.
Beta-carotene does not have an established UL. However, excessive consumption over a period of time can cause the skin to have a yellow-orange hue. Also, beta-carotene supplementation has been shown to increase the risk of developing lung cancer in smokers. (9)
In the grand scheme of things, consuming antioxidant-rich foods is simple. The daily consumption of fruits and vegetables will give you an ample amount of free radical-fighting ability.
The Dietary Guidelines for Americans (2015–2020) recommend 2 cups of fruit per day and 2.5 cups of vegetables per day to support a healthy lifestyle. (10)
According to NHANES data circa 2015, 9% of adults met the recommendation for vegetable consumption and 12% met the recommendation for fruit. (11)(12) Start by adding more fruits and veggies to your diet to combat the comorbidities that may stand in the way of a healthy future.