What are Antioxidants?

Antioxidants are often touted as miracle nutrients with the ability to prevent and treat diseases including diabetes. However, research regarding the role of antioxidants in diabetes prevention and management is conflicting. So what can people with diabetes take from current knowledge on antioxidants?

What are Antioxidants?

Antioxidants come in many forms including vitamins, minerals, and other substances found in foods. There are hundreds, if not thousands, of antioxidants – for a partial list and their food sources, see the chart on the next page. Antioxidants help protect cells from damage caused by harmful molecules called free radicals which can contribute to cancer, heart disease, and other diseases.  Free radicals are created as a result of normal body processes as well as exposure to pollutants like cigarette smoke and radiation. People with diabetes appear to have greater free radical production.  For this reason, researchers wonder whether antioxidant supplementation may help prevent complications among people with diabetes.

Antioxidants & Diabetes

Hyperglycemia (high blood glucose) produces greater free radical damage. This damage may contribute to kidney and eye complications as well as high blood pressure and changes to fat levels in the blood (dyslipidemia). Because antioxidants protect against free radical damage, researchers initially thought that taking antioxidant supplements may be helpful to people with diabetes. Unfortunately, research to date has not supported this hypothesis. Although some research has shown vitamin E to have some protective effects for the heart and blood vessels among people with type 1 diabetes, the same effects have not been found in those with type 2 diabetes. For people without diabetes, vitamin E and beta-carotene supplementation have been shown to increase risk of some cancers. Trials of the antioxidant α -lipoic acid have shown more promise than vitamin E. α-lipioc acid has improved symptoms of neuropathy among people with diabetic neuropathy when administered intravenously.

Overall, research on the role of antioxidants in diabetes is limited and has used high-dose antioxidant supplements. Only a few antioxidants have been studied, and not thoroughly enough to produce any definitive recommendations. Additionally, research has shown that medications commonly taken to treat diabetes and related complications, such as those for high cholesterol and high blood pressure, play more of an antioxidant-like role than antioxidant supplements themselves!

Foods, spices, and nutrients that contain antioxidants

While antioxidant supplements are not recommended for disease prevention or treatment, eating a variety of foods that naturally contain antioxidants can help protect against disease. When it comes to research regarding specific foods, spices, and nutrients, research is yet again unclear.

Foods that some preliminary research has reported to reduce blood glucose include bitter melon, Gymnema (a plant native to India and Africa), Korean ginseng, onions, garlic, and flaxseed meal.  However insufficient evidence is available to support these findings. While some research has shown cinnamon to be effective in reducing blood glucose, triglycerides, LDL (lousy)cholesterol, and total cholesterol levels in people with type 2 diabetes, other research has shown cinnamon to have no effect on these.

Nutrients that have been reported to reduce blood glucose include biotin, carnitine, vanadium, chromium, magnesium, zinc, and vitamins B3 (niacin), E, and K, all substances frequently seen on pharmacy and supplement store shelves. These ‘alternative remedies,’ many of which are considered to be antioxidants, have similarly not been tested adequately to prove their usefulness, and can interact with medications and be dangerous if taken without recommendation from a health professional.

The Take-Home Message

Current knowledge shows that the role of antioxidants in the prevention and treatment of disease is inconclusive and research does not support antioxidant supplement use for people with type 2 diabetes. The best strategy to help defend against free radical damage is to eat a healthy diet, engage in regular physical activity, and reduce stress whenever possible. Maintaining blood glucose levels in a healthy range will also help reduce free radical damage. Make a commitment to yourself to incorporate strategies to keep blood glucose levels on target each and every day!

Antioxidants & Their Food Sources


Found in

Carotenoids – there are more than 500 e.g. beta-carotene and lutein

Orange and dark green vegetables and fruit e.g. sweet potatoes, carrots, apricots, cantaloupe;  green leafy vegetables  e.g. spinach and kale

Flavonoids – aka polyphenols e.g. luteolin, resveratrol, quercetin, anthocyanins, isoflavonoids, and catechins

Fruit including apples, plums, prunes and berries e.g. blueberries, cranberries etc.; tea, soybean, red wine, peanuts, and dark chocolate

Isoflavones – related to isoflavonoids e.g.phyto estrogens

Nuts, flax and other oils, soy products, whole grain cereals, breads, and legumes


Tomatoes, watermelon, guava, papaya, apricots, pink grapefruit, and blood oranges

Vitamin A

Liver, sweet potatoes, carrots, milk, egg yolk, and natural cheeses

Vitamin C

Fruits particularly citrus fruits; vegetables e.g. sweet peppers, Brussels sprouts, broccoli, leafy vegetables, and russet potatoes

Vitamin E

Nuts, seeds and nut oils e.g. almonds, peanuts, pecans, sunflower seeds, peanut butter, safflower, corn, and soybean oils; leafy vegetables, sweet potato, avocado, mango, and broccoli


Seafood e.g. oysters and shellfish; whole grains, beans, nuts, potatoes, organ meats, dark leafy greens, and dried fruit


Meats e.g. liver, beef, chicken; oysters, clams, salmon, tuna, beans, soybeans, lentils, dried fruit, spinach, oatmeal, egg yolks, iron-fortified cereals, and whole grains
Note: meat sources of iron are more readily absorbed than vegetable sources. Eating animal foods or foods that contain vitamin C enhance the absorption of iron from vegetable sources.


Meats, with liver and kidney being primary sources; whole grains e.g. whole grain cereals, bulgur, and oats; nuts, seeds, wheat germ, legumes, and pineapple


Whole grains including rice, wheat etc.; brazil nuts, fish, shellfish, poultry, meat, beans e.g. kidney beans, pinto beans, black beans; and eggs


Meats e.g. liver, beef, lamb; seafood e.g. scallops, oysters, crab; fortified cereals, beans, nuts, whole grains, dairy products


Fresh, uncooked vegetables and fruits e.g. asparagus, potatoes, sweet peppers, carrots, onion, broccoli, avocados, spinach, garlic, tomatoes, apples, oranges, peaches, banana, and melon; milk products, and eggs

Coenzyme Q10

Oily fish e.g. salmon, tuna; organ meats e.g. liver; and whole grains

Alpha Lipoic Acid (ALA)

Vegetables e.g. spinach, tomatoes, peas, and Brussels sprouts

The content of this newsletter is for information purposes only. The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.