Beware outsized claims - mango peel may have anti-cancer properties but there isn’t enough evidence that it prevents or ‘fights’ cancers

Posts making the rounds on Facebook and Instagram claim that mango peels contain powerful antioxidants that can help fight cancer and diabetes, and advise people to eat the fruit with its skin to enjoy its benefits.

“JE, WAJUA? Maganda ya maembe yana ‘mangiferin, norathyriol and resveratrol’ misombo inayosaidia kuzuia na kupambana na baadhi ya saratani zikiwemo saratani za mapafu, koloni, matiti, ubongo na uti wa mgongo lakini ni muhimu ganda liwe limeoshwa vizuri na lisiwe na dawa za shamba (pesticides),” reads one of the posts in Kiswahili posted on 17 June 2023.

This translates to: “Did you know? Mango peels contain mangiferin, norathyriol and resveratrol, which are powerful antioxidants that may help prevent or fight some cancers, including lung, colon, breast, brain, and spinal cord cancers. However, it is important that the peel is washed properly to remove pesticides.”

Other versions of the claim add that mango peels “also contain triterpenes and triterpenoids, which are plant compounds that help fight cancer and diabetes” and that “it is scientifically recommended to take mango fruits without removing the peels to prevent different kinds of cancer and diabetes”.

But is the claim true? We checked.

Some evidence, though limited, support claims about mango peels

The claim appears to have been taken from WebMD, a US publisher of health and medical information. We discovered that some research has looked into mango peel extracts, while some studies looked into the individual compounds found in mango peel. 

A study published in Nature – a weekly international journal that publishes peer-reviewed research in all areas of science and technology – investigated whether mango peels and mango seed kernel extracts could treat breast cancer in female rats. 

They concluded that the mango extracts helped fight breast cancer in the rats and had a strong antioxidant effect. Antioxidants are substances that can prevent or reverse damage caused by free radicals – highly reactive chemicals that have the potential to damage cells. 

Free radicals can damage the DNA, which stores a person’s genetic information, and are thought to contribute to cancer and accelerate ageing. This damage is called oxidative stress. Healthy levels of oxidative stress are known as oxidative eustress.

The extracts were also found to have anti-proliferative effects, important in preventing or slowing the spread of malignant cells to surrounding tissues.

Another study published by the National Library of Medicine investigating the effects of mango peel extract on colon cancer cell lines found evidence that mango peel extracts had a selective anticarcinogenic effect on colon cancer cells. This study was done in vitro, meaning in isolated cells outside the body, not in a living organism. 

Further limited evidence for health benefits of fruit compounds

Some studies have shown that mangiferin, one of the compounds mentioned in the Facebook post, is found in different parts of the mango fruit, such as the peel, stalks, leaves, barks, kernel and seed, and that it has been shown to have anti-cancer properties. 

While this is the case, research suggests that its low oral bioavailability, or how much of what is taken by mouth eventually becomes available to the body, and low absorption in the body are factors that limit its clinical use.

A 2021 review of the available research, published in the journal Food and Chemical Toxicology, concluded that numerous studies suggested the compound could have a role to play in what is termed anti-carcinogenesis, which means preventing the processes that lead to cancer. 

Another review published in the journal Nutrients in 2016 had also investigated the topic. The researchers came to a similar conclusion, that available evidence suggested mangiferin might play a role in cancer prevention.

Scientific reviews are articles that analyse all the previously published literature on a certain topic, including individual research studies. Reviews are a good way of getting an overview of an area of research.

Pre-clinical trials show promising but not conclusive results

The claim also identifies other compounds, such as norathyriol and resveratrol, as powerful antioxidants in the peel that help fight diseases such as cancer and diabetes.

Studies have shown that norathyriol - a derivative of mangiferin - and resveratrol have anti-cancer properties. For example, norathyriol has been shown to have antioxidant, anti-inflammatory and anti-tumour effects.

Resveratrol has also been shown to have antioxidant, anti-inflammatory, cardioprotective and anti-cancer properties. Research suggests that resveratrol can even reverse multidrug resistance in cancer cells.

This research has been conducted in pre-clinical studies. This is when researchers look at the effects of something in test tube studies or on animals, before a drug can be developed and tested in humans. Tests in humans are called clinical trials. 

So we do not have support for the claims made about resveratrol from clinical trials, as it has multiple limitations that will first need to be addressed.

We also found studies that suggested that triterpenes and triterpenoids, the natural compounds found in plants, including mango, have potential anti-breast cancer and anti-diabetic properties. 

No large-scale clinical trials back up social media claims

Prof Edzard Ernst is an academic, doctor and researcher specialising in complementary and alternative medicine. He is an emeritus professor at the University of Exeter in the UK and has written a 2019 book to shed light on the facts and myths surrounding alternative medicine, including therapeutic regimens and diets.

We asked him if this could be an alternative treatment for various types of cancer. 

“There is no solid evidence for this,” he told us, adding that the claim was “firstly biologically implausible and secondly not supported by clinical evidence”.

Africa Check has previously debunked claims that antioxidants found in various jackfruit, eggplant, and rooibos tea can prevent cancer. (For more on this, read our factsheet on free radicals, antioxidants and medical myths.)

Free radicals and oxidative stress are thought to be a major cause of cancer. However, this doesn’t mean that a diet rich in antioxidants can prevent cancer.

There have been studies on cells in a test tube, called in vitro studies, which suggest that there may be a link between certain antioxidants and a reduced risk of developing certain cancers. However, large-scale clinical trials in humans have generally failed to show any benefit.

The majority of available evidence on this topic comes from in vitro studies, with some other studies using rodents. We do not know how mangiferin would affect cancer in the human body. This would need to be tested thoroughly before scientists can say whether it is effective, and safe.  

Furthermore, all the research involves using extracts or specific individual ingredients found in mango peel. Even if these show anti-cancer properties in future clinical trials, this does not mean that the peel itself would do the same.

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This report was written by Daniel Mwingira, the chief learning officer of Nukta Africa, a Tanzanian online media platform, and NuktaFakti, a fact-checking organisation in Tanzania, during the 2023 Africa Check Fellowship in Nairobi, Kenya. The fellowship was sponsored by the US  Department of State.