Vitamin E: When antioxidants may interfere with cancer treatment

Vitamin E is one of many antioxidants, although it is different than many antioxidants due to its other important roles in maintaining health. Among vitamins considered essential to human, only vitamin E and vitamin C are classified as antioxidants. Vitamin E is one of the four fat soluble vitamins, which means it must be consumed with a small amount of fat, approximately 4-5 grams to absorb daily recommended intake (DRI).

sunflower seeds

1/ The role of antioxidants:

Antioxidants, including vitamin E and vitamin C, have one important role in which they break down the “garbage” that may cause  many complications, including cancer. The garbage is generally categorized as free radicals and reactive oxygen species (ROS).

a/ Free radicals: Basically, every molecule entered in one’s body should have many electrons. These electrons help connect one compound with another. A normal compound should have pairs of electrons. Each pair, of course, must have two electrons. However, when the pair loses one electron, it becomes a free radical. The issue of these free radicals is that they do not behave like others. They can move from place to place, thus their damage is wide spread. Usually, when the body detects free radicals, it will try to combat with them by many means, one of which is the use antioxidants.

b/ Reactive Oxygen Species (ROS): ROS are not free radicals. When free radicals show up in the body, they interact with oxygen, leading to oxidation reaction. The outcome of this reaction is ROS. Basically, ROS is the result of oxidation reactions. ROS as well as free radicals can damage normal cells. The creation of ROS in human body is inevitable. Why? When the body breaks down food to store energy usually in the forms of lipids and glycogen, it does so via oxidation reaction, thus creating ROS. When one exercises, ROS is created via oxidation reaction while the body breaks down carbohydrates, protein, and lipids for energy. When ROS are released, they usually cause collateral damages to surround healthy cells.

2/ Functions of Vitamin E:

While vitamin E has many forms, the one suitable for absorption is alpha tocopherol.

#1 Vitamin E works as an antioxidant when the body breaks down lipids from food. Vitamin E is also an active antioxidant when the body breaks down stored fat cells for fuel during long work out sessions as well as weight loss.

#2 Vitamin E supports the immune system: alpha tocopherol keeps check on genes and metabolism processes thus it ensures healthy cells.

#3 Vitamin E reduces risks of heart diseases. When platelets floats in blood vessels long enough without being destroyed or recycled, they can stick together to create clutters which eventually stick to the walls of the blood vessels and to the walls or arteries. When this happens, some people may experience different symptoms such as high blood pressure and fatigue due to poor blood circulation. In the end, the final outcome is usually thrombosis. The cause of thrombosis is the narrowing of the walls of blood vessels. Vitamin E works to call enzymes to widen blood vessels.

3/ Recommended Daily Intake of Vitamin E

Vitamin E is required in International Unit (IU).

  • 0-6 months: 6 IU/day
  • 7-12 months: 7.5 IU/day
  • 1-3 years: 9 IU/day
  • 4-8 years: 10.4 IU/day
  • 9-13 years: 16.4 IU/day
  • 14 years and older: 22.4 IU/day
  • Lactating women: 28.4 IU/day

4/ Who are at risks of vitamin E deficiency?

  • Premature infants who weigh less than 1.5 kg at birth are at risk of vitamin E deficiency.
  • People who avoid fat in diet will suffer vitamin E deficiency in the long run
  • People with poor digestion (bile is not secreted enough to digest lipids)
  • People with liver diseases
  • People with cystic fibrosis
  • People with Crohn disease.

5/ Supplements must be used with caution

The risk of intoxication from ingestion of foods rich in vitamin E is very low. However many studies found that years of taking supplement at a dosage of 400 IU per day could cause blood thinning unrelated to vitamin K consumption among certain individuals having problems with blood coagulation and internal bleeding particularly among smokers.

The upper level (UL) of vitamin E is 1500 IU, provided that all comes from natural foods and not from manufactured sources. However, this UL is the highest amount that can be ingested without causing illness or death in 97% of healthy population. Individuals that are not considered healthy may face serious risks if they consume this much.

If one chooses to take supplement, please seek the smallest amount available such as 100 IU/day per tablet. The common dosages of most brands are 400 IU and 800 IU, though. However, many brands do not list vitamin E content as IU but in milligrams, which means customers need to convert mg to IU.


Sometimes doctors will recommend 400 IU and even a higher dosage under certain condition such as before and after surgeries or certain treatments. For daily usage, it is not advisable to consume large amount of supplement over a long period of time.

6/ Myths

#1 Vitamin E can cure heart diseases.

One study in the U.S found that patients with heart diseases who consumed vitamin E supplement at the dosage of 400 IU per day for 4.5 years did not improve. Those patients who continued the treatment for 2 more years had adverse consequenses: 13% had stroke and 21% was hospitalized.

Another study in Finland was conducted on 5,000 people who had their vitamin from food instead of supplement for 14 years showed improvement in heart conditions. However, this study did not measure how much vitamin E was consumed (patients reported on their own accord)

From these studies, one can see that the possible benefits of vitamin E among people with heart disease may be in the credit of natural food consumption rather than popping a pill.

#2 Vitamin E prevents cancer.

One study on 35000 healthy males above 50 years of age who took 400 IU vitamin E per day as supplement for 5 years did not show reduction in prostate cancer risk. After 18 months without using vitamin E, 17% of 35,000 men showed increased risk of prostate cancer.

Another study on the effect of vitamin E in preventing colon cancer on men and women showed different results. Women who consumed 37.5 IU/day in natural foods showed reduction in colon cancer. However, men who took 400 IU/day did not experience the same benefits.

Again, many studies found different results on efficacy of vitamin E on cancer prevention. All in all, it is best to consume vitamin E in natural forms instead of taking supplement unless directed by a health care provider.

7/ Vitamin E and drugs

#1 Anticoagulant and/or anti platelet medication ingested together with vitamin E can cause severe side effects. If one plans on taking vitamin E supplement at 400 IU/day should consult with his or her doctor.

#2 Simvastatin, vitamin B3: Strength and effect of these two substances can be reduced significantly when taken along with vitamin E, vitamin C, beta carotene (or any other antioxidants).

#3 Chemotherapy and radiation: The purpose of radiation and chemotherapy in cancer treatment is to eliminate cancerous cells by oxidation reaction. Therefore, the use of antioxidants, such as vitamin E, can counter the effects of the treatment. Of course, when patients with cancers are under professional healthcare, they should be advised beforehand about what to consume and what not.

8/ Factors affecting vitamin E content

During storage and cooking, certain factors may affect vitamin E content. Although vitamin E is considered durable than many other nutritional substances, most vitamin E in cooking oil is reduced by 20-30% after 6 months of storage. However, improper storage such as exposing cooking oi to light or air can completely destroy vitamin E content within 3 months. Thus, it is best to keep oil in opaque ad airtight containers, not clear plastic or glass bottles. It is up to one’s preferences to store the oil in refrigerator or room temperature.

Cooking with foods rich in vitamin E at high temperature (e.g 172 Celsius or 340 Fahrenheit for 3 hours will reduce vitamin E content by 50%. At this rate, after 6 hours, vitamin E content of the food is virtually zero. Thus, cooking method required long cooking hours at high temperature such as roasting, broiling, or even lower temperature for longer hours such as slow cooker, should be minimized. With that perspective, it is reasonable to expect that the greater the temperature, the faster the rate at which foods rich in vitamin E is destroyed.

Take home message: with foods rich in vitamin E, minimize their contact with air, heat, and light.

9/ List of common foods rich in vitamin E

  • Almond, raw, 1 oz (28 grams or 12 whole almonds): provides 50% daily value of vitamin E for an adult
  • Almond, roasted, 28 grams (1 oz): 34%
  • Sunflower seeds, raw, 1 oz (28 g): 50%
  • Sunflower seeds, roasted, 1 oz (28 g): 34%
  • Hazelnut, roasted, 1 oz (28 g): 22%
  • Peanut, roasted, 1 oz (28 g): 11%
  • Peanut butter (dry roast, no oil added), 1 oz (28 g): 15%
  • Olive oil, 14 g (15 mL or 1 Table spoon): 13%
  • Sunflower oil, 14 g (15 mL or 1 Tbs): 28%
  • Corn oil, 14 g, (15 mL or 1 Tbs): 10%
  • Soy bean oil, 14 g (15 mL or 1 Tbs): 6%
  • Avocado, raw, 150g: 21%
  • Spinach, cooked, 200 g: 28%
  • Turnip greens, cooked 150 g: 20%
  • Asparagus, cooked, 200 g: 20%
  • Olives, pitted and canned, 135 g: 15%
  • Swiss Chard, 175 g, cooked: 22%
  • Beet greens, cooked, 150 g: 19%
  • Kale, cooked, 130 g: 7%
  • Bell pepper, raw, 100 g: 10%
  • Shrimp, shelled, cooked, 100 g: 15%