Dietary supplements include nutrients, vitamins, and minerals that are essential for human health, as well as a wide variety of non-essential nutrients, such as phytochemicals, hormones, and herbs. As a general rule, dietary supplements should never replace whole foods.
Dietary supplements, especially those that have not been well studied, are best used in moderate doses. Use of vitamin and mineral supplements at doses of more than a few multiples of recommended levels can raise safety concerns as can the intake of high doses of herbal and botanical supplements.
The belief that an herbal or botanical supplement is “natural” and therefore can be only beneficial, even in high doses, is clearly incorrect. Many vitamins and herbal compounds are toxic at high levels. The current lack of regulatory oversight of dietary supplements has led to misleading health claims and, in many cases, hazardous doses and contaminants in marketed products. Consumers should be warned about the use of high-dose supplements of any type.
One of the rationales for taking nutritional supplements stems from observations of lower cancer risk among those who eat diets high in fruits and vegetables, which are rich in essential vitamins and minerals. However, there is no evidence that any nutritional supplements can reproduce the apparent benefits of a diet high in vegetables and fruits.68,105 Pills sold as being equivalent to fruits and vegetables are, in fact, not equivalent, despite the marketing claims of their manufacturers.
Although some in vitro and animal studies have suggested possible benefits with high doses of single vitamins and minerals, there is little evidence from human epidemiological or clinical studies to confirm their safety or efficacy. In fact, a nutrient previously thought to be both safe and beneficial (beta carotene) was actually found to increase lung cancer risk in heavy cigarette smokers after it was tested in two large studies.106,107
This suggests that nutritional supplements containing high levels of single nutrients (i.e., greater than the Dietary Reference Intakes and the tolerable upper intake limits) may have unanticipated adverse effects on cancer survivors.
As mentioned, a current area of controversy is the advisability of using nutritional supplements during cancer treatment. Folic acid and its derivatives, for example, should be avoided with methotrexate administration, as this nutritional supplement can alter the efficacy of the chemotherapeutic agent.108,109 For this reason alone, it is always advisable for health care providers to question survivors under their care about any vitamin supplement use during treatment.
As previously noted in the section “Phase I: Cancer Treatment,” page 155, there is some reason to suspect that high doses of antioxidant supplements might interfere with free radical mediated-cytotoxic mechanisms of radiotherapy and some chemotherapeutic agents.
Despite the lack of firm evidence, it may be reasonable to use nutritional supplements after the active treatment phase for cancer survivors who cannot eat enough to obtain sufficient nutrients. The effects of illness and its treatment, as well as dietary deficiencies, can weaken the body, including the immune system. Although many commercial supplements are promoted to enhance the immune system, some can actually suppress the immune system. 110
Cancer survivors should be especially cautious of regimens that suggest high supplemental doses of any single nutrient, or drastic eating changes, as a deficiency of any essential vitamin or mineral during cancer treatment and recovery can weaken the immune system.
A reasonable health recommendation to aid recovery after treatment would be for cancer survivors to use a balanced multiple vitamin and mineral supplement (once or twice a day) to correct possible deficiencies. Multivitamin supplements of this type are manufactured by a wide variety of companies, with levels of nutrients usually at approximately the levels recommended for daily consumption [now expressed on labels as the % Daily Value (DV)], formerly known as the Recommended Daily Allowance.
The DV is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97% to 98%) individuals in a specific life stage and gender group, and is intended primarily for use as a goal for daily intake by individuals.12-16
The DV is set considerably higher than the estimated average requirement to account for variability in absorption and need. Although nutritional supplementation at doses higher than twice the DV may sometimes be recommended by physicians based on consideration of an individual’s diet and disease state, it is generally unwise to initiate such regimens without medical consultation.
One nutritional supplement, beta carotene, has shown some promise in correcting oral leukoplakia, a premalignant lesion of the mouth.111 Nevertheless, overall, beta carotene supplements are more harmful than beneficial.106,107 Early results from uncontrolled trials suggesting that vitamin C and beta carotene were beneficial for cervical cancer were not supported in a properly controlled trial.112 And, there is no good evidence that taking supplements of vitamins A, C, or E at doses above the DV is associated with any clinical benefit.113
espite the many gaps in scientific knowledge about supplements, many cancer survivors take supplements and are eager to learn more about them. Information provided by manufacturers, retailers, or distributors of supplements is rarely unbiased. Health care providers should be sure to question survivors under their care about whether they are using nutritional and herbal supplement products, especially during chemotherapy or radiation therapy.
Survivors should also be counseled against self-prescribing high doses of supplements. It is not wise to assume the safety of high-dose supplements, as there are many uncertainties about their effects and their interactions with other treatments.114-116
Nutritional Issues in Complementary and Alternative Medicine
As defined by the ACS, “complementary” therapies are supportive methods used to complement evidence-based treatment.11 Examples include meditation to reduce stress, acupuncture for pain, and ginger for nausea. Complementary methods are not given to cure disease, rather they may help control symptoms and improve well-being.
“Alternative” refers to treatments that are promoted as cancer cures. They are unproven because they have not been scientifically tested, or were tested and found to be ineffective. If used instead of evidence-based treatment, the survivor may suffer, either because helpful treatment is not received or because the alternative treatment is harmful. Personal testimonials are often offered as evidence of the efficacy and safety of these methods, and the treatment is often claimed to be effective in other diseases as well as cancer.
Nutritional methods used within complementary and alternative medicine generally encompass vitamin and mineral supplements, herbal and botanical supplements, and dietary regimens.100-104, 110,117-138
Cancer survivors may be interested in using complementary or alternative medicine, including nutritional therapies, to enhance the effects of treatment, to protect against treatment-related side effects, or to improve quality of life during treatment and recovery. The use of such therapies has greatly increased in recent years.117
Survivors may believe that such therapies are “natural” and therefore also harmless, an assumption that may not be correct. It is important for health care providers and survivors to discuss the use of complementary or alternative therapies so that survivors are fully informed regarding both possible benefits and risks.
In the absence of firm scientific evidence from controlled clinical trials, survivors need to make decisions about complementary and alternative therapies based on uncertain claims. Data that do not meet the usual standards of scientific proof include anecdotal reports of efficacy, uncontrolled trials, traditional use suggesting a lack of harm, and the plausibility of biological mechanisms of action.
Some herbal and botanical supplements have a long history of use in other cultures, suggesting safety when used according to traditional methods. Only a few of these traditional supplements have been studied scientifically to evaluate their effects on cancer. Little is known about the use of commonly available herbal and botanical supplements by cancer survivors. This lack of knowledge is a strong argument for more clinical research and physician education in this area. Reliable information about the functions of supplements and their therapeutic doses is difficult to find.
For a few supplements, clinical and preclinical research provides evidence of benefit in some situations. However, for most, current information must be considered preliminary, as there have been so few controlled clinical trials. Even in the best cases, currently available research findings can only be regarded as preliminary.
Survivors should discuss their choices with their practitioners so that regimens can be tailored and monitored to reduce the possibility of adverse effects such as drug/nutrient interactions or toxicities.
The following nutritional therapies are highlighted because of their popularity among cancer survivors. Several other therapies are discussed in the longer version of this document that is available online.
For information on additional complementary and alternative therapies, refer to the American Cancer Society’s Guide to Complementary and Alternative Cancer Methods (Atlanta, GA: American Cancer Society, 2000) or call the American Cancer Society (1-800-ACS-2345).
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