Grapes have been cultivated by man for millennia and are used in winemaking. It can also be eaten raw and enjoyed daily with other food and beverages. Apart from being highly popular, it is rich in antioxidants, vitamins and minerals and well-loved worldwide. Notably, there is another reason to love grapes. It might protect you from sunburn and reduce your risk of skin cancer!
A peer-reviewed, small study [1] published in the scientific journal Antioxidants and conducted by Pezzuto and his colleagues in US universities found that consuming grapes protected 29 human volunteers against ultraviolet (UV) skin damage.Â
Researchers from universities in New York and Massachusetts recruited healthy volunteers who agreed to consume two ¼ cups of grapes processed as whole grape powder daily for two weeks. The amount of daily intake of grapes is equivalent to three servings. The investigators induced a 1 cm sunburn in the healthy volunteers and measured this following intake of three servings of grapes for two weeks.
Investigators measured the responses of the skin to UV radiation before and after the study (two weeks intake of grapes). At the end of two weeks, a third of the healthy volunteers demonstrated increased resistance to sunburn. The study’s authors explained that this increased resistance was likely due to active compounds in grapes called polyphenols. Polyphenols are naturally-occurring compounds present in grapes that act as antioxidants.
The healthy volunteers who demonstrated increased resistance to sunburn were found to have unique metabolic and microbiome characteristics following their blood, urine and gut microbiome analysis. The high diversity of the gut microbiome, which means the microbiome hosts a wide variety of microorganisms, has been linked to optimal health.
Following analysis, the authors conclude that there might be a potential link between the healthy volunteers’ genes, their skin and gut health. This means that an individual’s genetic profile, along with their metabolic and digestive traits, can help them resist sunburns after eating grapes.
The lead author, John Pezzuto, concludes that dietary consumption of grapes can enhance resistance to skin UV irradiation, with the extent of the response more significant in individuals who have a lower Fitzpatrick skin type. The Fitzpatrick skin type characteristics are based on four skin types: lower skin types as fairer or whiter, and skin type IV as brown.
Although the study was small and findings could not be generalized to a larger group of individuals, the initial results are promising since increasing resistance to UV irradiation can reduce the risk of skin cancer. However, not all individuals have the same response to UV irradiation after eating grapes. These individuals with little or no improvement in skin sunburn after eating grapes were those with higher Fitzpatrick skin type or brown skin. The majority of the subjects in the study had skin type III.
The report adds to the growing evidence of the protective effects of grapes against ultraviolet radiation. This is the first clinical trial that recruited human volunteers to examine the effects of eating grapes against UV radiation on the skin. The authors also cited US studies conducted in 2008, another in 2019 and the latest in 2020. These three studies found that the consumption of grapes prevented skin cancer in mice exposed to ultraviolet light.
Notably, grapes are rich in polyphenols, and antioxidants are known to have many benefits.
What are antioxidants?
Antioxidants can be naturally produced in the body or taken from fruits and vegetables. Antioxidants are necessary for the body since they scavenge excess free radicals, prevent early cellular damage, and reduce the risk of many diseases.
One of the naturally-occurring antioxidants is glutathione [2]. Glutathione is manufactured in the liver from the amino acids glycine, glutamate, and cysteine. To combat oxidative stress, tissues and cells in the liver are well-endowed with mechanisms that include metal-sequestering proteins and enzymes that metabolize reactive metabolites or radicals. The most important antioxidant in the liver is glutathione.
Other antioxidants can be sourced from fruits, vegetables and plants. Polyphenols are examples of antioxidants found in fruits such as grapes. Currently, there are approximately 8,000 polyphenols in plants. Human and animal model studies found that polyphenols have the following benefits:
- Antioxidant properties
- Anti-inflammatory properties
- Preventive or therapeutic effects for neurodegenerative diseases, cardiovascular disease, and obesity [3].
Considering the vast uses and benefits of antioxidants, it is no wonder that the polyphenols present in grapes are associated with preventing skin cancer.
How do polyphenols potentially prevent skin cancer? Polyphenols are known to have a cytotoxic effect or the ability to induce toxicity in cells. Research studies show that polyphenols can activate cells that can kill cancer cells.
A review [4] has shown that polyphenols increase cytotoxic T cells that kill tumours, which in turn can inhibit tumour growth. Further, the same review revealed that polyphenols also have antiproliferative effects on tumour cells. Cell proliferation is described as a biological process where the number of cells undergoes cell division to increase their population.
What is UV light?
In many parts of the world, fair-skinned populations are at greater risk of skin cancer than those with darker skin. In fact, skin cancer is identified as the most common type of cancer among fair-skinned people [5]. The incidence, morbidity, and mortality rates of this type of cancer pose a crucial public health issue.
Ultraviolet radiation (UV) is the leading cause of skin cancers [4]. So, how does UV cause skin cancer? UV is known to cause damage to the DNA and mutations in the genes, which subsequently leads to the development of skin cancer. Hence, UV is classified as a non-specific damaging agent and a mutagen [6]. Further, UV is identified as a tumour promoter and tumour initiator.
To reduce the risk of skin cancer, fair-skinned populations must be exposed to less UV. However, UV is vital to human health since it mediates vitamin D synthesis and skin endorphins. Hence, UV has mixed and complex effects on the human skin and overall health. Nevertheless, too much exposure to UV is associated with a profound risk to health, which includes pigmentary changes, atrophy, malignancy, and wrinkling.
UV is linked to the three most common types of skin cancer:
- Squamous cell carcinoma
- Basal cell carcinoma
- Malignant melanoma
The potential effects of three servings of grapes daily in preventing skin cancer or treating skin cancer are now supported by a small clinical trial. However, studying the impact of grapes in the long-term and recruiting a larger group of individuals could help strengthen the initial results presented by Pezzuto and his colleagues.
According to Cancer Research UK [7], at least 2400 deaths yearly are due to melanoma skin cancer, the most common type of skin cancer. In the US, the American Academy of Dermatology reports that about 9,500 people are diagnosed with skin cancer every day. It is the most common type of cancer in the US, with one in five Americans developing skin cancer during their lifetime [8].
Considering the impact of skin cancer on individuals affected by the disease, it is essential to know how supplements might prevent the development of this type of skin cancer. It is still too early to tell if grape extracts or eating three servings of grapes could treat skin cancer or prevent its development due to the small sample size in the study by Pezzuto and colleagues. However, initial results are promising and showed the potential of grapes in preventing skin cancer.
[1] https://www.mdpi.com/2076-3921/11/12/2372#B4-antioxidants-11-02372
[2] https://www.sciencedirect.com/topics/neuroscience/glutathione
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6160559/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8471058/
[5] https://pubmed.ncbi.nlm.nih.gov/20883261/
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709783/
[7] https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/melanoma-skin-cancer
[8] https://www.aad.org/media/stats-skin-cancer
