"...all doctors should be able to diagnose and treat nutritional deficiencies."

Royal College of Physicians. Nutrition and Patients: A Doctor's Responsibility. London 2002


This page has been printed from the www.stewartnutrition.co.uk web site.

Cancer – Active or Recently Treated

Though vitamins and minerals are essential for life they may also be essential for the growth of many cancers.  Attempts to lower the risk of cancer developing by using high doses of some vitamins and minerals with anti-oxidant properties have generally been unsuccessful and some have resulted in an increase in the risk of cancer developing especially in smokers and those exposed to asbestos

However it is also clear that many people with cancer become undernourished and develop nutritional deficiencies as a result of their cancer and sometimes, in part, as a consequence of their treatment.  Striking the right balance is not always easy.

Important Facts about Nutrition and Cancer

  • Numerous studies show that a healthy diet with a good intake of a variety of fruits and vegetables is the best way to reduce the risk of developing cancer and nutritional supplements are no substitute for this.
  • Attempts to lower the rate of cancer by giving high doses of nutrients especially antioxidants that are found in fruit and vegetables to healthy people in large clinical trials have not resulted in a decline in the rate of cancer and may increase it. See the Cochran review.
  • For those with cancer, at present there is no dietary or supplement regime that is of proven value in improving the outcome.
  • Trials of nutritional supplements with the intention of reducing the prevalence of cancer or heart disease by the use of supplements of anti-oxidants, folic acid and other B vitamins have not generally resulted in beneficial outcomes and have been associated with higher rates of certain types of usually common cancers.
  • Some nutrients, especially folic acid and vitamin B1 – thiamine, may be growth-promoting for certain cancers (see below)
  • Some anti-cancer treatments act by disrupting the metabolism of certain nutrients especially folates (by the use of methotrexate) and high intakes of folates in the diet or folic acid from supplements or fortified food may reduce the potential benefit of such treatment (see below)
  • The risks and benefits of taking supplements are probably influenced by a variety of both genetic and environmental factors.  These in turn influence the risk of deficiency being present (potential benefit) or cancer developing (potential harm).  As we get older both the risk of mild deficiency increases as does the risk of having an early sub-clinical cancer, which may or may not develop to become a significant problem

Some Sensible Advice

The charities Cancer Research UK and the MacMillan/Backup give some brief and sensible advice on this difficult issue along the lines of;

  • The best way to get your essential nutrients is from a healthy varied diet
  • Do not take supplements without first discussing it with your oncologist or nursing specialist

This is good advice but a little more can probably be said within this framework about specific problems.

Rapid Weight Loss

Some patients with cancer lose weight rapidly due to a combination of reduced food intake and increased demand due to the metabolic effects of the cancer.  The excessive weight loss can lead to a loss of muscle bulk and the development of anaemia and nutritional deficiencies a situation termed cancer cachexia.  Some research suggests that high intake of omega-3 essential fatty acids from oily fish and other sources [internal link – Dietary Sources of Essential Nutrients] and sometimes supplements may be beneficial.

Such patients may also require specialist dietetic advice to maintain energy and protein intakes and are at risk of developing nutritional deficiencies that could influence their appetite (anaemia, iron, zinc and vitamin B), immune function (zinc and vitamin B) and energy level (vitamins B and C, potassium and magnesium).  The use of nutritional supplements in such patients requires careful clinical judgement (see below)


Antioxidants, Chemotherapy and Radiotherapy

A review of the use of antioxidant supplements in patients undergoing chemotherapy or radiotherapy concluded that although such supplements may reduce the side-effects associated with treatment they may also protect the tumour cells from treatment-induced oxidant damage thus potentially reducing the therapeutic outcome.
The authors state “On the basis of our review of the published randomised clinical trials, we conclude the use of supplemental antioxidants during chemotherapy and radiation therapy should be discouraged because of the possibility of tumour protection and reduced survival.”

This view is not shared by all especially those in the alternative sector.

The author shares the concern of many cancer specialists that use of nutritional supplements in patients with an active cancer or one that is undergoing treatment may well be counterproductive and has expressed this view previously [Davies S & Stewart A. Nutritional Medicine. 1987. Pan Books: London].  There are other views and patients should ideally be assessed individually.


Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg JB.  Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy?  J Natl Cancer Inst.  2008;100:773-83.

Simone CB 2nd, Simone NL, Simone V, Simone CB.  Antioxidants and other nutrients do not interfere with chemotherapy or radiation therapy and can increase survival, Part 2.  Altern Ther Health Med. 2007;13:13

Vitamin B 1- Thiamine

The growth of some cancers may be enhanced by vitamin B1 - thiamine because they require it for the production of the sugar ribose which is an essential component of DNA and RNA nucleic acids.  Rapidly growing cells of all kinds need to manufacture DNA and RNA and thus have a high demand for thiamine.

In a significant percentage of patients with gastric and gastroesophageal junction cancers the cancer tissue may over-express a mutated form of the thiamine-dependent enzyme transketolase which is crucial in the production of ribose from the non-oxidative pentose phosphate pathway.  In work by German researchers this finding was most likely in poorly differentiated gastroesophageal tumours in male patients.

Further laboratory experiments have shown that thiamin may stimulate the growth and thiamin inhibitors suppress the growth of some cancers and there is the potential for treating some cancers by use of thiamine inhibitors. 

It would thus seem prudent to avoid giving thiamin to patients with rapidly growing tumours unless they have a specific need for it.

Staiger WI et al.  Expression of the mutated transketolase TKTL1, a molecular marker in gastric cancer.  Oncology Reports 2006;16:657-61

Dietary Folates and Folic Acid

A similar but more complicated situation upholds with another B vitamin folate/folic acid.  This B vitamin plays a key role in cell division as it too is needed by enzymes involved in the transfer of single carbon molecules that are required in the synthesis of DNA and RNA.
The drug methotrexate is widely used to treat many types of cancer and acts by disrupting folate metabolism.

However a good intake of dietary folates, which are found in good amounts in green, especially leafy, vegetables as well as some fruits, is associated with a lower risk of many cancers developing.  This is thought to be because adequate folate is needed for enzymes that help to repair aberrant or damaged DNA that if not repaired could lead to cancerous change. 
Thus folate may have two separate roles;

  • protecting against the initiation of cancer
  • potentially promoting the growth of cancer once it has formed.

In practice many older people have precancerous changes in various tissues, which may be considered to be a natural consequence of ageing influenced by inherited factors as well as environmental factors such as smoking, alcohol and diet.  Supplements of folic acid might thus either aid in the repair of precancerous tissue or advance their growth.  The anti-folate drug, methotrexate, was first used in the treatment of cancer when it was observed in the 1940s that supplements of folic acid worsened the outcome in children with acute leukaemia.

More recently there have been numerous trials where folic acid has been given, sometimes in large amounts, to either prevent cardiovascular disease or cancer.  Many such trials are still ongoing.  The outcome of some of these trials have been reviewed by Smith et al and in some trials, contrary to expectations, there has been an increase in the development of cancers rather than a reduction.  There is also evidence that since the introduction of widespread fortification of food with folic acid in 1998 in North America, which has resulted in both a significant reduction in mild folate deficiency and the risk of neural tube defect births there has been a rise in the incidence of colorectal cancer in both the US and Canada.  However the evidence does not constitute proof of a causal effect and it is plausible that improved folate status will result, eventually, in a decline in the incidence of some cancers.

Following the interest in folic acid and other B vitamins acting to lower the level of homocysteine, an amino acid that, when elevated, is a marker for heart disease, numerous trials using supplements of folic acid, usually in doses between 400 and 800 ug per day with or without other B vitamins, were undertaken.  Many such trials are ongoing but those that have been completed or terminated early due to lack of benefit have revealed a modest increase in the incidence of cancer in those who were taking folic acid (+ other B vitamins) when compared with those on placebo.  When the various trials are completed the data will be pooled by the B-Vitamin Trialists Collaboration and incident cancers will be one of the end points that they will be looking at.

For the time being those with cancer should be very cautious about any use of folic acid supplements especially if they are taking methotrexate and they should seek the advice of their oncologist/radiotherapist.


Smith DA, Kim Y-I, Refsum H.  Is folic acid good for everyone?  Am J Clin Nutr 2008;87:517-33.
Dameshek W. Editorial: the use of folic acid antagonists in acute leukaemia. Blood 1948;3:1057-8
Ebbing M et al.  Mortality and cardiovascular events in patients treated with homocysteine-lowering B vitamins after coronary angiography. A randomized controlled trial.  JAMA. 2008;300:795-804

Advice for Those Recently Diagnosed with Cancer

In view of the foregoing evidence of an association between high intakes of certain nutrients from supplements and the development of cancer some advice needs to be given about the use of supplements by those who have recently been diagnosed with cancer.

The author recommends that;

  • In those who are taking nutritional supplements and have been recently diagnosed with or are strongly suspected of having cancer that all supplements of vitamin B, folic acid, multivitamins, antioxidants (beta-carotene, retinol and vitamin E), calcium and vitamin D are stopped until an appraisal of your nutritional state and the risks and benefits of continuing with them can be made.
  • In those who have recently been diagnosed with cancer that no new supplements of vitamin B, folic acid, multivitamins, antioxidants (beta-carotene, retinol and vitamin E), calcium and vitamin D are commenced without the express agreement of your specialist/oncologist. 
  • The use of prescribed nutritional supplements (most often calcium and vitamin D, fish oils or low dose multivitamins/vitamin B complex) are continued but their use should be reviewed by your specialist/oncologist.

In areas of uncertainty the advice of your specialist/oncologist should be sought.  Additionally it is prudent to also check that any intended use of nutritional supplements does not conflict with known major contraindications particularly in those with liver or renal problems or hypercalcaemia. 

Copyright Dr. Alan Stewart M.B.B.S.M.R.C.P. (UK)M.F. Hom.
47 Priory Street, Lewes, East Sussex. BN7 1HJ
Tel 01273 487003 Fax: 01273 487576