Researchers looked at dozens of studies about vitamins and supplements that cancer patients take to feel better during and after treatment. They found that some supplements like amino acids and N-acetyl cysteine might help with certain side effects like skin damage from radiation or nerve pain from chemotherapy. However, most of the research isn’t strong enough to say for sure that these supplements work. The good news is that most supplements caused only minor side effects, though some vitamins in high doses can be risky. Doctors need more research before they can confidently recommend which supplements cancer patients should take.

The Quick Take

  • What they studied: Whether vitamins and nutritional supplements can safely help cancer patients manage side effects from treatment like skin damage, nerve pain, and mouth sores
  • Who participated: This review analyzed 52 previous research studies that included 250 different clinical trials testing 18 different supplements for 16 different cancer-related problems
  • Key finding: Two supplements showed moderate evidence of helping: amino acids for radiation skin damage and N-acetyl cysteine for preventing nerve pain in people with stomach cancers. Several other supplements showed weaker evidence of possible benefits. Most supplements were safe, but high doses of some vitamins caused problems.
  • What it means for you: If you’re a cancer patient, some supplements might help with side effects, but talk to your doctor first. The evidence isn’t strong enough yet to recommend them without medical guidance. Most supplements are safe in normal doses, but don’t assume all supplements are harmless.

The Research Details

Researchers conducted an ‘umbrella review,’ which means they looked at many previous research reviews instead of doing their own experiments. They searched five major medical databases for the best-quality reviews and studies about nutritional supplements used by cancer patients. They focused on supplements used to manage side effects like mouth sores, skin damage, and nerve pain—but they didn’t look at supplements for pain, anxiety, or depression since those are already covered in other guidelines.

They found 52 high-quality reviews that had analyzed 250 different clinical trials. These trials tested 18 different supplements (like vitamins, amino acids, and probiotics) for 16 different cancer-related problems. The researchers then ranked the evidence from strongest to weakest based on how well the studies were done and how consistent the results were.

This approach is important because it gives doctors and patients the clearest picture of what actually works. Instead of looking at just one study, which might be wrong or biased, researchers looked at many studies together. This helps separate supplements that truly help from those that just seem to help by chance. It also helps identify which supplements are safe and which ones might cause problems.

The researchers found a major problem: almost all 52 reviews they analyzed were of low or very low quality. This means the original studies had weaknesses like small numbers of patients, poor study design, or unclear results. This is important because it means we can’t be very confident in the findings. When evidence quality is low, it means doctors should be cautious about recommending these supplements without more research.

What the Results Show

The strongest evidence came for two supplements: amino acids and oral proteolytic enzymes (special proteins that break down other proteins) for reducing the severity of radiation-induced dermatitis, which is painful skin damage from radiation therapy. The other strong finding was that N-acetyl cysteine might prevent chemotherapy-induced peripheral neuropathy (nerve damage in hands and feet) in people with gastrointestinal cancers.

Several other supplements showed weaker evidence of possible benefits. Glutamine, zinc, probiotics, and melatonin might help with oral mucositis (painful mouth sores). Vitamin E, omega-3 fatty acids, glutamine, and other amino acids might help prevent nerve damage from chemotherapy. However, the researchers emphasized that this evidence is ’low to very low certainty,’ meaning we can’t be confident these supplements actually work.

The good news about safety is that most nutritional supplements caused only minor side effects like upset stomach or mild nausea. However, some supplements were concerning: high-dose Vitamin A caused serious adverse events, and both zinc and Vitamin E showed dose-related problems, meaning higher doses caused more side effects.

The review identified that probiotics and melatonin might help with mouth sores, though the evidence is weak. Zinc also appeared in multiple studies for mouth sores but had dose-related safety concerns. The researchers noted that many supplements had been studied, but the quality of those studies was generally poor, making it hard to draw firm conclusions.

This research builds on previous work by bringing together all the recent evidence in one place. It confirms what many doctors have suspected: while some supplements might help with cancer side effects, we don’t have strong enough evidence yet to recommend them routinely. The findings suggest that some supplements are worth studying more carefully, while others need to be abandoned because they don’t show promise.

The biggest limitation is that almost all the studies reviewed were of low quality, which means the conclusions are weak. The researchers couldn’t find enough high-quality studies to make strong recommendations. Another limitation is that the review didn’t look at whether supplements might interfere with cancer treatments themselves—an important safety question. The review also excluded studies on pain, anxiety, and depression, so it doesn’t cover all ways supplements might help cancer patients. Finally, many studies had small numbers of patients, which makes it harder to trust the results.

The Bottom Line

Based on moderate-certainty evidence: Cancer patients with gastrointestinal cancers who are at risk for nerve damage from chemotherapy might consider N-acetyl cysteine, but only under doctor supervision. For radiation skin damage, amino acids show promise but need more research. For other supplements: The evidence is too weak to recommend them routinely, though they’re generally safe in normal doses. Always talk to your oncologist before taking any supplement, as some might interfere with cancer treatment.

Cancer patients experiencing side effects from treatment should care about this research, especially those dealing with nerve pain, mouth sores, or skin damage. Oncologists and cancer care teams should use this to guide conversations with patients about supplements. People considering supplements as cancer prevention should know this research is about managing side effects, not preventing cancer. People taking high-dose vitamins should be aware of potential risks.

If supplements do help, benefits would likely appear within weeks to a few months of consistent use, depending on the side effect being treated. However, given the weak evidence, many patients may not notice improvement. It’s important to give supplements a reasonable trial period (usually 4-8 weeks) while monitoring for side effects, but don’t expect dramatic results.

Want to Apply This Research?

  • Track specific cancer side effects daily (rate mouth sores, skin irritation, or nerve pain on a 1-10 scale) before starting a supplement and continue tracking weekly to see if symptoms improve. Record the supplement name, dose, and date started.
  • If considering a supplement based on this research, set a reminder to take it consistently at the same time daily, and schedule a check-in with your oncologist within 2 weeks to discuss whether it’s helping and if it’s safe with your other treatments.
  • Create a simple log tracking: (1) which supplement you’re taking and the dose, (2) the specific side effect you’re trying to manage, (3) your symptom severity rating each week, and (4) any side effects from the supplement itself. Share this log with your doctor at each visit to make informed decisions about continuing the supplement.

This research summary is for educational purposes only and should not replace professional medical advice. Cancer patients should never start, stop, or change supplements without consulting their oncologist or medical team first. Some supplements can interfere with cancer treatments or interact with medications. The evidence reviewed here is generally weak to moderate, meaning we cannot make firm recommendations. Individual responses to supplements vary greatly. Always discuss supplement use with your healthcare provider before beginning, especially during active cancer treatment.