Diet supplements – do they help in cancer treatment?


Cancer patients often turn to various types of dietary supplements in the hope that they will improve their health. Is it really worth trusting these types of products in the process of oncological treatment?

When patients learns that they have cancer, their life changes dramatically. Faced with illness, they often question the status quo and introduce changes to their daily life, hoping to reverse the course of the disease. After entering the traditional path of treatment, the patients also usually modify their diet, looking for healthier products. They introduce physical activity into their life, even if previously movement was not a permanent element in everyday life. At the same time, some patients turn the market of dietary supplements and alternative medicine, looking for the most adequate products that will improve their health.

Diet supplements – what are they?

Dietary supplements are not drugs. They should serve us as a supplement to a balanced diet. They are food products whose task is to supplement deficiencies. Importantly, dietary supplements are not subjected to the same regulatory standards as drugs.

Diet supplements in cancer treatment

Agnieszka Surwiłło-Snarska, MSc, clinical dietitian, working every day with cancer patients at the National Institute of Oncology in Warsaw, stresses out that there are only two indications for the inclusion of vitamins and minerals in cancer patients: prove deficiency (e.g. after determining new ones) in the blood or after the appearance of deficiency features), or the clinical condition that will lead to the deficiency (e.g. gastrectomy patients – vitamin B12).

Meanwhile, a significant proportion of cancer patients use vitamin preparations, as well as alternative medicine preparations, thus concealing this fact from the examination.

Increased risk supplements

The most disturbing among cancer patients is the use of alternative medicine preparations on their own. The effectiveness of this type of treatment has not been confirmed by scientific studies. Patients, on the other hand, tend to abandon the drugs of evidence-based medicine in favor of preparations with an unproven effect. Such behavior often causes the patient’s health to deteriorate.

Preparations independently used by cancer patients include amygdalin, infusions of vitamin C, or herbal mixtures.

Amygdalin is a naturally occurring substance, for instance in the pits of some fruits. It is a very controversial substance that contains the cyanide radical and is therefore toxic to humans. So far, no strong scientific evidence has emerged that amygdalin has any therapeutic effect on cancer.
Vitamin C overdose may cause diarrhea, that may contribute to the development of malnutrition.
Inconspicuous herbs can also do more harm than good. Be especially careful of St. John’s wort and ginseng, which interact adversely with drugs used in chemotherapy and radiotherapy.

The use of inappropriate preparations by oncological patients carries many risks. Such action increases the risk of complications, malnutrition, and interactions with drugs used in cancer therapy. As a consequence, it may lead to the postponement or even discontinuation of proper oncological therapy.

Agnieszka Surwiłło-Snarska, MSc, points out.

There are no supplements or diets to cure cancer. However, there are still patients who come to the dietitian’s office with such conviction.

Right diet – the best source of vitamins and minerals

Where to look for a source of vitamins and minerals? In a well-balanced diet! No dietary supplement can replace proper nutrition, which is a very important element in fighting the disease. Unfortunately, more than half of cancer patients show symptoms of malnutrition, and every fifth patient dies as a result of cachexia – a disease that develops in parallel with the neoplasm, which manifests itself with exhaustion and gradual deterioration of the body. Therefore, it is worth focusing on what the patient eats and in what amounts. It is advisable that the oncological patient remains under the care of a clinical dietitian throughout the treatment process, who will recommend appropriate supplementation if necessary.

Author: Natalia Wiszniewska,

Expert consultation: Agnieszka Surwiłło-Snarska, MA, Clinical Nutritionist, Department of Clinical Nutrition, National Institute of Oncology in Warsaw.


“Czy stosować suplementy u pacjentów onkologicznych – co wybrać, a czego unikać?’, A. Surwiłło- Snarska, Dział Żywienia Klinicznego, Narodowy Instytut Onkologii w Warszawie, 2021 ,

“Suplementacja witamin u chorych onkologicznych. Część I – witaminy z grupy B”, M. Badian, T. Dzierżanowski, Medycyna Paliatywna 2018; 10 (3): 131-136,

“Dieta w chorobie nowotworowej”, lek. Aleksandra Kapała, Wydawnictwo Buchmann, 2016.

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