Taking Vitamins During Cancer Treatment

Taking vitamins or other supplements during cancer treatment may have benefits, but there can also be risks. Cancer fatigue may be one reason people turn to vitamins and other supplements or because they believe they have anti-cancer and anti-toxicity properties.

However, the effects of taking vitamin and mineral dietary supplements during cancer treatment are uncertain and some might interfere with the effectiveness of chemotherapy or other cancer therapies.

This article discusses the possible risks and benefits of supplements and the reasons why dietary supplements may or may not be recommended by your oncologist or healthcare team.

When Do Oncologists Recommend Vitamins?

There are several reasons why your healthcare provider may recommend dietary supplements.

To Treat Nutrition Deficiencies

With side effects like loss of appetite and nausea that are common with cancer, nutritional deficiencies can occur. Talk to your healthcare provider about this possibility.

Some researchers have theorized that supplementation could help reduce cancer cachexia. Cachexia is a syndrome of unintentional weight loss, muscle wasting, and decreased appetite that affects up to 50% to 80% of people with advanced cancer.

It is estimated that cachexia contributes directly to 20% of cancer deaths. Cancer cachexia is extremely challenging to treat and most nutrition supplements have not been found to aid in this syndrome. However, there is some evidence that omega-3 fatty acids may be helpful.

To Reduce Cancer Fatigue

A 2017 review concluded the following may help with energy levels in cancer survivors:

• Supplementing the diet with ginseng, ginger, or probiotics 
• Following a dietary pattern that reduces inflammation, such as the Mediterranean diet or other plant-based diets
• Increased protein intake to preserve muscle mass and body composition

Another study found that an extract of a South American plant called guarana—along with a healthy diet—helped reduce cancer-related fatigue in people being treated for breast cancer.

To Prevent a Second Cancer

Since cancer treatments such as chemotherapy and radiation therapy predispose survivors to other cancers, the hope has been that the risk of a second cancer could be reduced with the use of antioxidant supplements.

Just as supplements (as opposed to dietary antioxidants) have not shown consistent results in preventing cancer, there is not much evidence that these supplements would help prevent a second cancer in survivors.

To Decrease Toxicity of Treatments

Studies have been mixed concerning antioxidants increasing or reducing the toxicity of chemotherapy, but some research suggests they may improve the quality of life for some people during cancer treatment. However, the research results are mixed on whether antioxidants are beneficial or harmful during chemotherapy.

To Increase Life Expectancy

An oft-quoted study supporting the use of vitamin supplements during cancer treatment showed an increase in the length of survival. This 2009 study revealed a longer-than-expected median survival time, with 76% of the patients living longer than was predicted (median increase in survival of 5 months).

It’s important to note that this was a very small study (41 patients) conducted with people considered to have end-stage cancer who had a predicted life expectancy of only 12 months. These patients were treated with a supplement of coenzyme Q10, vitamins A, B, and C, selenium, folic acid, and for those without lung cancer, beta-carotene.

Vitamin D and Cancer

For several reasons, vitamin D deserves special consideration concerning its role in cancer treatment.

The first reason is that it may be difficult to get an adequate amount of vitamin D by dietary measures. While the recommended daily allowance is 400 to 800 international units (IU) per day, depending upon age, studies looking at cancer prevention have looked at higher numbers: up to 1,000 to 2,000 IU per day.

We think of fortified milk as being a source of vitamin D, but at about 120 IU per glass, it would require drinking almost seven glasses per day just to reach the 800 IU recommended for a 70-year-old person (much less the dose studied in cancer prevention studies).

The sun is a good source of vitamin D, requiring only short amounts of time with arms and face exposed to absorb upwards of 5,000 IU. That is, you need to live in a region where you can be outside with your arms and face exposed and the angle of the sun at your latitude allows the absorption of vitamin D-producing rays. This can be a problem in northern climates.

For this reason, many healthcare providers recommend a supplement of vitamin D3.

Who Should Take a Vitamin D Supplement?

A simple and inexpensive blood test can provide you and your healthcare provider with a measure of your blood level of vitamin D. While this won’t tell you what your total body “store” of vitamin D is, it can be used to determine if a supplement is needed and guide treatment.

It is estimated that almost 20% of middle-aged and older adults in the U.S. are vitamin D deficient and 34% have vitamin D insufficiency.

Importance of Vitamin D

Vitamin D is not an antioxidant. It functions more like a hormone than a vitamin in the body.

There have been many studies that have evaluated the role of vitamin D both in cancer prevention and cancer treatment.

• Low blood levels of vitamin D are associated with an increased risk of several cancers.
• A high vitamin D blood level is associated with a lower risk of developing breast and colorectal cancer. 
• People who have higher vitamin D levels at the time of cancer diagnosis have longer survival rates from lung cancer than those with lower levels.
• Low vitamin D levels appear to increase the risk of breast cancer spreading (metastasizing).
• A large National Cancer Institute study found that people with high vitamin D levels were 76% less likely to die from their disease than people with low levels of vitamin D.

Since some cancer treatments predispose to osteoporosis, and vitamin D aids calcium absorption, an adequate vitamin D level may also affect the quality of life for some cancer patients.

Vitamin D supplementation may also help with cancer fatigue. One small study showed cancer patients with higher vitamin D levels reported less fatigue and improved well-being.

Even though much of the research shows a positive role of vitamin D for some people with cancer, it’s important to talk to your healthcare provider before using a supplement. Your healthcare provider will want to monitor your levels to see if they change if you begin a supplement.

The normal range of values may not be the ideal range for someone with cancer. For example, the reference range for normal vitamin D levels is 30–80. Yet some studies suggest that a level of 50 is better than a level of 31.

Vitamin D supplementation is not for everyone. There are potential side effects, including, kidney stones, if levels are too high.

Why Your Oncologist May Not Recommend Vitamins

There are many types of cancer, and even with a single type of cancer, there are tremendous differences. Add in each unique person, with their own body characteristics and other medical conditions, and it’s easy to see why taking supplements during cancer treatment is very complex.

There are several reasons why your oncologist may recommend that you avoid vitamin or mineral supplements. Sometimes the particular reason may not be obvious (such as knowing the vitamins that may affect blood test results with cancer), and it’s important to ask your healthcare provider what you should avoid and why. These are some reasons to avoid vitamin supplements:

Possible Interference With the Benefits of Treatment

One of the main reasons oncologists don’t recommend vitamin and mineral supplements or antioxidant formulas is they could counteract the effects of chemotherapy or radiation therapy.

Free radicals in our bodies (produced by substances such as tobacco smoke, radiation, and normal metabolic processes) can damage the DNA in our cells (mutational damage which can lead to cancer.) This damage is called “oxidative damage” since the reaction involves oxygen. Antioxidants produced by our bodies and ingested in our diets protect cells by neutralizing these free radicals and preventing oxidative damage.

This theory is supported by a 2019 study in which postmenopausal women who took antioxidant supplements during chemotherapy and radiation therapy for breast cancer had worse recurrence-free survival and a higher mortality risk (they were 64% more likely to die).

Another 2019 study found antioxidant supplements may promote the spread (metastasis) of lung cancer by inhibiting the breakdown of a protein called BACH1.

Interaction With Chemotherapy

Vitamin C may reduce the effectiveness of some chemotherapy agents, including vincristine, doxorubicin, methotrexate, cisplatin, and imatinib. So far, these effects have been seen only in some laboratory and animal studies.

How vitamin C is given may also influence its effectiveness and risks. Some studies of intravenous (IV) vitamin C use in people with cancer showed it improved quality of life and reduced cancer-related side effects.

Vitamin C and Hormonal Therapy

Studies looking at human breast cancer cells in a lab have found that vitamin C decreased the effectiveness of tamoxifen. In these studies, it was thought that vitamin C interfered with apoptosis (cell death) in cancer cells.

Vitamin C and Targeted Therapy

Targeted therapies are newer cancer treatments that target specific pathways in the growth of cancer cells. In animal studies, vitamin C appeared to reduce the anti-cancer activity of the targeted therapy Velcade (bortezomib). Velcade is used for people with multiple myeloma and some types of lymphoma.

Some of the risks may be more theoretical. A 2007 review of studies from 1983 to 2005 found no evidence that antioxidant supplements interfered with chemotherapy, and some researchers believe that antioxidants may help to protect normal cells without interfering with the effectiveness of cancer therapy.

This review included studies using glutathione, vitamin A, vitamin C, vitamin E, ellagic acid, selenium, beta-carotene, melatonin, and N-acetylcysteine. The review concluded that antioxidants may improve tumor response to treatment and survival rates while also aiding patients’ tolerance to treatment.

Another systematic review found evidence that using antioxidants with chemotherapy resulted in less toxicity, allowing people to complete full doses of therapy. The exception was one study that showed an increase in toxicity in those using a vitamin A supplement. This review evaluated studies using N-acetylcysteine, vitamin E, selenium, L-carnitine, Coenzyme Q10, and ellagic acid.

Interaction With Other Medications

There are many examples of possible interactions, but a simple example is that of vitamin E, which could potentially increase the risk of bleeding in people who are taking the blood thinner Coumadin (warfarin).

Interactions That Affect Blood Tests

Some vitamins such as biotin (vitamin B7) may interfere with the assays done to provide some laboratory results. Of note is that biotin may be present in many combination vitamin supplements.

Dietary Sources vs. Supplements

We don’t have as many studies looking at the use of antioxidants during cancer treatment, but the use of these supplements with the goal of cancer prevention has revealed some interesting findings.

For example, a high dietary intake of beta-carotene was associated with a lower risk of developing lung cancer, but a review of studies looking at the use of a beta-carotene supplement found that the risk of lung cancer was increased, especially in smokers.

Findings were similar with prostate cancer: Dietary vitamin E consumption is associated with a lower risk, but a study evaluating vitamin E supplements found an increased risk.

Theories have been proposed to explain why supplements may increase cancer risk. Perhaps there are phytochemicals (plant-based chemicals) in food aside from beta-carotene (or other antioxidants) that are responsible for the cancer prevention properties.

Another theory that’s been proposed is that receiving one antioxidant as a supplement may result in the body absorbing less or using less, of another important antioxidant.

Sometimes taking a supplement for one concern may raise another. An example is a study in which people with melanoma were treated with selenium. Researchers found that the supplement was associated with a lower risk of developing a second cancer in the lungs, colon, or prostate, but was also associated with an elevated risk of diabetes.

Most oncologists recommend eating a healthy diet and do not believe the antioxidants derived from foods pose a threat to the effectiveness of cancer treatments.

Method of Study

Interpreting some of the information on antioxidants during cancer treatment is difficult for many reasons, one of which is the different methods used.

• Some studies are done on rodents, and effects in rodents may or may not be the same as those in humans.
• Many studies have been done on human cancer cells grown in a dish in a lab. While this does give us some good information, it doesn’t take into account the myriad of other processes going on in the human body that could alter the response seen in the lab.
• Vitamins and antioxidants may have different effects on normal cells and cancer cells. For example, in lab studies, cancer cells appear to take up vitamin C better than normal cells.

There are also special cases that can’t be addressed when studies look at the general population. For instance:

• Vitamin C in people with glucose-6-phosphatase deficiency can lead to hemolysis.
• People with hemochromatosis are at risk of iron overload with iron supplements.

The role of vitamins and antioxidants can also vary depending on particular treatments. For example, vitamin C may reduce the effectiveness of radiation but may also reduce the toxicity.

Considerations for Taking Vitamins

If your oncologist does recommend a supplement, there are a few things to keep in mind.

• Again, only use vitamins or minerals (or any other nutritional or herbal supplements) if your oncologist does not think these could be harmful in your particular situation.
• The potential risks and benefits noted above are just a glimpse to demonstrate why vitamin and mineral supplements need to be considered individually for each person. Your healthcare provider may recommend using or avoiding vitamin or mineral supplements for additional reasons.
• Always bring all over-the-counter medications and supplements with you to each oncology appointment.
• Don’t be fooled by advertising that says “natural” or “plant-based.” An example is hemlock. It is natural and plant-based, and it can even be grown organically. Yet it’s thought by many that it was the poison referred to in Romeo and Juliet and implicated in the death of the philosopher Socrates. Many strong chemotherapy drugs are plant-based.
• Use only the recommended dose. More isn’t necessarily better and could be harmful. Keep in mind that supplements often contain levels of vitamins and minerals that far exceed what you would get eating a normal diet. In addition, there is little regulation of these supplements in the United States, and some products could contain traces of pesticides and heavy metals.
• Use only high-quality vitamins and minerals. Check if they have been evaluated by ConsumerLab.com. Also, check if there is a USP or NF seal on the label, indicating that quality control testing has been done on the product.
• Continue to discuss your intake of vitamins and minerals at each follow-up visit. Many clinical trials are in progress, and information could change—in either direction—as we learn more.

Summary

Vitamin and mineral supplements during cancer treatment may have risks as well as benefits. Risks include counteracting the effects of chemotherapy or radiation, interfering with targeted therapies, and interacting with other medications. Benefits may include improving nutritional deficiencies, cancer fatigue, and cachexia.

Talk with your oncologist before taking any supplements to understand the potential risks or benefits associated with the type of cancer you have and the treatments you are receiving.