Natural doesn't mean harmless during cancer treatment
When a cancer diagnosis arrives, many patients reach instinctively for supplements and remedies that feel natural and safe — not knowing that the body makes no such distinction between 'natural' and 'pharmaceutical.' Professor Carol-Ann Benn of Netcare Milpark Hospital in Johannesburg has made it a pillar of her practice to remind patients that chemistry does not honour good intentions: the same compounds that promise wellness can quietly unravel the precise biochemical work of cancer treatment. The call is not for suspicion of all supplements, but for honesty — because only the full picture allows an oncology team to protect the patient they are trying to heal.
- Cancer patients are unknowingly undermining their own treatment by taking supplements and vitamins they believe are harmless, creating a hidden threat inside the very protocols designed to save them.
- The danger is biochemical and invisible — liver enzymes that process nearly half of all chemotherapy drugs can be accelerated or blocked by common supplements, causing drugs to either vanish too quickly or accumulate to toxic levels.
- High-dose antioxidants like vitamins A, C, and E may actually shield tumour cells from the oxidative damage that chemotherapy and radiation are engineered to deliver, turning a wellness habit into a shield for cancer.
- Everyday chronic medications — heartburn drugs, anticonvulsants, anticoagulants, anti-inflammatories — layer additional risks onto treatment, each capable of altering drug absorption, breakdown, or toxicity in unpredictable ways.
- Oncology teams at multidisciplinary centres like Netcare Milpark are urging patients to disclose everything before changing any supplement or medication, so that treatment protocols can be individually calibrated rather than quietly compromised.
A cancer diagnosis often sends patients searching for anything that might help — vitamins, herbal remedies, supplements promising to boost immunity or fight inflammation. What many do not realise is that these products, precisely because they feel natural and harmless, can quietly sabotage the treatments designed to save their lives.
Professor Carol-Ann Benn, who directs the breast cancer centre at Netcare Milpark Hospital in Johannesburg, has seen this pattern enough times to make full disclosure a cornerstone of her practice. She asks patients to tell their oncology team about everything they take beyond regular food — chronic medications, over-the-counter drugs, vitamins, supplements. The reason is not bureaucratic caution. It is chemistry. Cancer drugs operate within a narrow window, and small shifts in how much drug reaches the bloodstream — or how long it stays there — can mean the difference between effective treatment and wasted months.
The mechanism is often invisible. Nearly half of all chemotherapy drugs are processed by liver and gut enzymes that certain supplements can speed up or slow down, causing drugs to either lose their effect or accumulate dangerously. Vitamin B supplements illustrate the complexity: high doses can disrupt chemotherapy's metabolic processes, yet for patients with treatment-related nerve damage, the same vitamins may offer relief. The same supplement can help one patient and harm another, depending entirely on which drugs they are taking.
Antioxidants present a similar paradox. In a healthy diet they protect cells, but high-dose antioxidant supplements — vitamins A, C, and E, beta-carotene, glutathione — can shield cancer cells from the very oxidative damage that chemotherapy and radiation are designed to inflict. Common chronic medications add yet another layer: heartburn drugs reduce absorption of some oral cancer treatments, anticonvulsants accelerate the breakdown of chemotherapy agents, and even everyday anti-inflammatories can interfere with how the body clears other medications.
Benn's centre operates as a true multidisciplinary hub — surgeons, oncologists, pathologists, dietitians, genetic counsellors, and specialised nurses working in coordination — because cancer treatment demands constant vigilance about everything a patient puts into their body. The safest path is straightforward: before starting, stopping, or changing anything, patients must speak with their oncology team. For cancer patients, full disclosure is not merely good practice. It is essential.
A cancer diagnosis often sends patients searching for anything that might help. Vitamins. Herbal remedies. Supplements that promise to boost immunity or fight inflammation. The problem is that many people don't realize these products—precisely because they feel natural, harmless, even beneficial—can quietly sabotage the very treatments designed to save their lives.
Professor Carol-Ann Benn, who directs the breast cancer centre at Netcare Milpark Hospital in Johannesburg, has seen this pattern enough times to make it a cornerstone of her practice. She emphasizes that patients must tell their oncology team about everything they're taking outside of regular food: chronic medications, over-the-counter drugs, vitamins, supplements, all of it. The reason is not bureaucratic caution. It's chemistry. Cancer drugs—particularly chemotherapy, immunotherapy, and targeted therapies—operate within a narrow window. Small shifts in how much drug reaches the bloodstream, or how long it stays there, can mean the difference between effective treatment and wasted months. "This is not about blame," Benn says. "Many people simply do not know that supplements, vitamins and over-the-counter products can behave like medicines in the body."
The mechanism is often invisible to the patient. Nearly half of all chemotherapy drugs and most oral cancer medications are processed by a family of enzymes located mainly in the liver and gut. Some supplements speed up this process, causing the drug to clear from the system faster—and lose its punch. Others slow it down, allowing the drug to accumulate to dangerous levels. Some products interfere with how the drug is absorbed in the first place. The interactions are not theoretical. They are biochemical facts with real consequences.
Vitamin B supplements illustrate the complexity. High-dose B vitamins can interfere with certain chemotherapy drugs by disrupting metabolic and genetic processes. Yet for patients experiencing treatment-related nerve damage, B vitamins can provide relief. The same supplement can help one patient and harm another, depending on which drugs they're taking. This is why generic advice—even well-intentioned advice from friends or online forums—is dangerous. Only the oncology team, knowing the specific drugs, doses, and patient history, can navigate these waters safely.
Antioxidants present a similar paradox. In a healthy diet, they protect cells from damage and reduce inflammation. But during cancer treatment, high-dose antioxidant supplements—vitamins A, C, and E, beta-carotene, glutathione—can actually shield cancer cells from the very damage the treatment is meant to inflict. Chemotherapy and radiation work by generating free radicals and oxidative stress inside tumors. A patient taking high-dose antioxidant supplements may be inadvertently protecting the cancer cells they're trying to kill.
Common chronic medications add another layer of risk. Heartburn drugs reduce the absorption of some oral cancer medications. Anticonvulsants speed up the breakdown of certain chemotherapy agents. Antibiotics and antifungals can increase bone marrow suppression and liver toxicity. Anticoagulants can interact with chemotherapy in unpredictable ways—sometimes increasing bleeding, sometimes increasing clotting. Hormonal therapies can counteract anti-estrogen drugs. Even nonsteroidal anti-inflammatory drugs, the kind people take for everyday aches, can interfere with the body's ability to clear other medications.
Benn established the Netcare Milpark Breast Care Centre of Excellence, which has earned international accreditation from the American College of Surgeons. The centre operates as a true multidisciplinary hub—surgeons, radiation oncologists, medical oncologists, pathologists, radiologists, genetic counsellors, physiotherapists, dietitians, and specialized nurses all working together. This structure exists precisely because cancer treatment is not simple. It requires coordination across specialties and constant vigilance about what patients are putting into their bodies.
The safest path forward is straightforward: before starting, stopping, or changing anything—a supplement, a vitamin, a medication—patients must discuss it with their oncology team. This applies even to everyday items like green tea and coffee, which contain compounds that may interact with cancer drugs in ways that depend on the specific treatment, the dose, and the individual patient. The conversation takes time, but it is time well spent. The alternative is treatment that looks good on paper but fails in the body, or side effects that could have been prevented. For cancer patients, full disclosure is not just good practice. It is essential.
Citações Notáveis
This is not about blame. Many people simply do not know that supplements, vitamins and over-the-counter products can behave like medicines in the body.— Professor Carol-Ann Benn, Netcare Milpark Hospital
The safest approach is to discuss all medicines, supplements and vitamins with your oncology team before starting, stopping or changing anything.— Professor Carol-Ann Benn
A Conversa do Hearth Outra perspectiva sobre a história
Why would a patient take a supplement during cancer treatment in the first place? Aren't they focused on the prescribed drugs?
Often they're trying to help themselves. A cancer diagnosis is terrifying. People want to boost their immune system, reduce inflammation, manage side effects. Supplements feel like they're taking action. And many come with claims backed by studies—just not studies done on people undergoing chemotherapy.
So the problem isn't that supplements are inherently bad?
Exactly. Vitamin C can help with wound healing. B vitamins can ease nerve damage from treatment. Antioxidants protect healthy cells. But the dose matters enormously, and the context matters more. A supplement that's protective in a healthy person can become dangerous during active cancer treatment.
Can you give me a concrete example of how this goes wrong?
Take antioxidants. Chemotherapy kills cancer cells partly by creating oxidative stress—essentially controlled damage. A patient taking high-dose vitamin E supplements is essentially trying to neutralize that damage. They're working against their own treatment without knowing it.
And the patient might never know why their treatment failed?
That's the risk. They complete their chemotherapy, thinking they did everything right, and the cancer progresses. The oncologist might not even know about the supplements if the patient didn't mention them—and many patients don't, because they don't think supplements count as "medicine."
So this is about communication?
It's about communication, but also education. Patients need to understand that natural doesn't mean harmless, and that their oncology team isn't being controlling by asking about supplements. They're trying to protect the treatment itself.
What should a patient do if they're already taking something?
Tell their oncology team immediately. Don't stop it on your own—some supplements need to be tapered. Let the team decide what stays, what goes, and what might need adjustment. That's the only safe way.