In contrast with tropical areas, papaya is not very popular in certain areas of the world, though the global market has already stepped deeply into peoples’ habits in almost every country. However, while papaya is typically available as chopped fresh or dried fruit, many of its greatest benefits actually come from its seeds. The seeds have a spicy flavor and can be enjoyed raw, dried, crushed or frozen; they can actually act as a substitute for black pepper. Even the scientific community is yet investigating the properties of papaya seeds. Some preliminary analyzes, however, have revealed the presence of some interesting classes of chemical substances known for their antioxidant, anti-inflammatory and antitumor capacity, belonging to the class defined as “chemo-preventatives”.
papaya seeds contain various polyphenols that can exert anti-inflammatory activity in some contexts. Among these, the main ones are ferulic acid, caffeic acid, quercetin and rutin. A very recent study confirmed that papaya extract can suppress allergic asthma in mice. Additionally, the seeds contain papain and chymopapain, enzymes similar to pineapple bromelain, which have the ability to resolve inflammation and promote healing. In Latin America, a paste made from seeds was traditionally applied to burns and wounds to speed recovery. The seeds are also commonly used in folk medicine for the benefit of rheumatoid arthritis, osteoarthritis, and other inflammatory conditions.
Papaya seeds contain other phytochemicals including tocopherols (forms of vitamin E). These, together with quercetin enhance the activation of AMP-activated protein kinase (AMPK), as well as the inhibition of COX-2 cyclooxygenase expression. In addition, a range of phytochemicals with a great strength of anti-inflammatory effect, such as vitamin C, benzyl-isothiocyanate, β-carotene and lycopene can be found in various parts of papaya fruits, including in the pulp of the seeds. It has been shown that these phytochemicals inhibit the cellular synthesis of pro-inflammatory cytokines including TNF-alpha and IL-6, which are produced in rheumatoid arthritis and Crohn’s disease, justifying the popular use of the seeds.
Kidney and liver disease
Papaya seeds were traditionally used in traditional Chinese medicine to detoxify the liver and body. The fruit was also known to protect against chemically induced liver damage. While papaya seeds have been documented to be extremely useful in treating alcohol-induced cirrhosis and malnutrition, studies have yielded mixed results. Only a couple of studies have shown how seed extract can prevent cell damage induced by certain liver toxins (industrial solvents) in lab rats. Papaya seeds are known to protect the kidneys from toxin-induced kidney failure. A study published in African Health Science found that the seeds have the ability to reverse acetaminophen-induced kidney damage. While paracetamol it is not harmful to the stomach, it can pose a threat to kidney and liver cells; over time it may increase the risk of chronic kidney failure.
Cancer prevention and treatment
A study published in Journal of Nutrition and Cancer looked at the chemo-preventive properties of the seeds. They found that the flavonoids in the seeds prevented tumor transformation through antioxidant and anti-inflammatory mechanisms. In particular, the compounds protected both healthy cells and their genetic material. Since the seeds are also rich in isothiocyanates, compounds that prevent cancer, they improve the transcription of proteins called “tumor suppressors”. Therefore, introducing papaya seeds into the diet can be an inexpensive way to gain access to chemoprevention.
Isothiocyanates are the same phytochemicals found in vegetables such as cauliflower, broccoli, Brussels sprouts, turnips, cabbage and savoy cabbage (Brassicaceae). They are most effective against cancer of the lung, liver, esophagus, stomach, small intestine, colon, and mammary gland. There are several studies showing the in vitro effect of papaya seed extract on various cancer cell lines. One of them published last year shows that the standardized alkaloid extract of papaya seeds caused experimentally induced liver tumors to recede in laboratory rats. The animals also showed less tumor cachexia, less bleeding and circulating levels of alpha-fetoprotein.
Hypertension, diabetes and cholesterol
Papaya seeds have documented cardiac benefits. Carpine, an alkaloid found in seeds, slows the heart rate by lowering blood pressure. In terms of effectiveness, it has even been compared to digitalis, a drug generally prescribed for heart patients. Since they are enriched in polyphenols (flavonoids), the seeds can effectively control blood glucose levels, hypertension and hypercholesterolemia. Agada and colleagues showed that ethyl acetate extract from papaya seeds significantly reduced postprandial glucose levels in diabetic rats. In addition, the extract of the seeds, such as that of fermented papaya, reduced transaminase levels, improving insulin sensitivity of the liver and stabilizing the blood glucose level in diabetic patients Since isothiocyanates are also effective inducers of enzymes for detoxification, they can help normalize the production of cholesterol in the liver as a response to a metabolic imbalance.
Seeds and fruit are a digestive aid that can kill harmful amoebas and parasites. The seeds contain a class of sulfur-based molecules called isothiocyanates which have shown toxic action on worms. One study found that the dried seeds effectively killed human intestinal parasites without harmful side effects. Their consumption, therefore, offers a natural, harmless, inexpensive and readily available monotherapy and a preventive strategy against intestinal parasitosis, especially in tropical communities. Another study found that the seeds protected the digestive tract from ulcers by increasing mucus production and decreasing stomach acid.
Papaya seeds are a primitive form of birth control with measurable benefits. In the mouse studies, male mice that were fed 20mg/kg weight of papaya seeds, orally for 60 days, were significantly less fertile than the control group. In the rabbit studies, the animals received 20mg per day for 150 days. Within 45 days, sperm motility and viability were severely affected. By day 75, only 1% of the sperm were viable. The researchers found that the sperm’s acrosome, core and tail were damaged by the seeds. The heads and tails were also detached on many specimens. During the study, the rabbits achieved a 0% fertility rate with no negative side effects or loss of libido. Very singularly they were reversible: 45 days after the end of the study, fertility was restored. These effects were also confirmed on human spermatozoa in 2019.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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