Cancer and nutritional supplements

There is a large variety of vitamin and mineral supplements available in the shops and pharmacies, but do we really need to be taking them? The American Dietetics Association (ADA) recommends taking a nutritional supplement if one’s diet is inadequate, or lacking certain food items. 

The use of vitamin supplements has been making headlines recently for all the wrong reasons. It is true that large doses of single supplements have (especially) been shown harmful in certain patients. 

Many people take anti-oxidants to prevent them from getting sick, however, this is not true for all vitamins. Vitamin C in pharmacological dosages has shown to be harmful in patients with head and neck cancer. Interestingly, smokers are prone to be deficient of vitamin C, so they might actually benefit from a vitamin C supplement.

People with known dietary deficiencies, or those who are not following a healthy diet can take supplements that is in line with international recommendations.

A multivitamin is ideal for women who are planning to become pregnant, are pregnant, or breastfeeding.

Which vitamins and food groups you should consume daily?

We try to get our daily dose of vitamins and minerals through our diet, aiming to reach 100% of our Recommended Daily Allowance (RDA). We’d like this to be practical – so if you are eating five fruits, a bowl of whole grains and a good serving of lean protein, you could get away with not taking a vitamin and mineral supplement.

A dietitian can also help assess whether a dietary supplement would be necessary. When we see patients in consultation we look at their medical history to look for possible nutrient – medication interactions as certain drugs don’t work well with certain supplements. We also look at certain supplements which contain herbs that can actually raise a person’s blood pressure.

Patients on active cancer therapy should not be taking single nutrients without consulting their dietitian or doctor as this can be harmful to their health.

We need to remember that our body is an intricate biochemical system where everything works in harmony. It is worrying to see people taking many single supplements on their own, instead of supplementing their diet with the help of a healthcare professional. An example of a combination of dietary supplements is when someone takes calcium and magnesium supplements together, as these two minerals can compete with one another.

If you don’t take them in conjunction with one another the body gets depleted of the one mineral. That is why multivitamins are often a safer choice. If you want to take a dietary supplement, rather go for the “cocktail approach”, where you can take a multivitamin to make sure that the vitamins and minerals are balanced.

Water soluble vitamins and minerals, for example B-vitamins, are excreted though our urine after our body has absorbed what it needs. So if we are supplementing 600% of our RDA of vitamin B12 for example, then we are actually urinating most of the vitamin out and spending unnecessary money on this supplement. The RDA is always written on the back of a dietary supplement.

Keep in mind that the supplement industry is a multi million rand industry, and there is no governing body regulating the production, or selling thereof in South Africa. This is a reason for great concern. Marketing is a very powerful tool, and people are focussed on staying healthy, which is great, but it does put our pockets in a vulnerable position.

Take home this message: the food based dietary guidelines are our first approach in leading a healthy lifestyle. We should aim to eat a healthy diet and so a dietary supplement may not be necessary. Should a deficiency be present or a higher requirement of a certain vitamin or mineral is needed, then a dietary supplement can be recommended. If you want to take a supplement, take a multivitamin instead of supplementing one specific vitamin or mineral. Before taking single supplements, consult a dietitian or your doctor.

To find a dietitian in your area, go to


Berna Harmse is a private practicing dietitian in Cape Town, she holds a MSc in Dietetics and has a special interest in oncology nutrition. She is also an external lecturer at Stellenbosch University Division of Human Nutrition.