Papaya (Carica papaya) is a tropical fruit enjoyed globally, but its small, dark seeds have a long-standing reputation in traditional medicine across various cultures. This traditional use is often centered on the seeds’ ability to affect reproductive health, leading to the persistent belief that consuming them may cause infertility. Investigating this claim requires distinguishing between traditional practices, laboratory findings, and the realities of human consumption.
The Basis of the Claim: Traditional Use and Animal Studies
The concept of using papaya seeds for fertility control is deeply rooted in ethnopharmacological practices, particularly in parts of South Asia and Africa. Traditional healers in these regions have historically used the seeds as a male contraceptive and, in some cases, to induce abortion in women. This history suggests that the seeds contain potent compounds recognized for their biological activity in the reproductive system.
Modern scientific investigation has largely focused on male fertility, using concentrated extracts of the seeds in animal models like rats, mice, and langur monkeys. These studies have consistently demonstrated that high doses of the seed extract can significantly reduce sperm count and impair sperm motility. For instance, high-dose oral administration in male rats resulted in a dose-dependent reduction in fertility, sometimes leading to zero fertility within 60 days of treatment.
A key finding across these animal studies is that the effects are often reversible once consumption of the seed extract ceases. In langur monkeys, for example, long-term azoospermia (absence of sperm) induced by the extract fully reverted to near-normal sperm parameters within 150 days of stopping the treatment. This reversibility has positioned papaya seed extracts as a promising candidate for the development of a reversible male contraceptive.
How Papaya Seed Compounds Affect Reproductive Physiology
The biological effects observed in animal models are attributed to specific bioactive compounds naturally present in the seeds, including alkaloids, flavonoids, and isothiocyanates. Benzyl isothiocyanate (BITC) is one of the most studied compounds and is believed to be a primary contributor to the seeds’ reproductive effects. These compounds appear to interfere with the process of sperm production and maturation.
The antifertility action is primarily seen in the male reproductive system, where the compounds disrupt spermatogenesis, the process of sperm cell maturation in the testes. Studies show that the extract can cause morphological defects in sperm and reduce the count of spermatocytes and spermatids, indicating a maturational arrest. The compounds may also act post-testicularly, directly affecting the sperm’s movement and vitality after formation, potentially by causing DNA fragmentation and affecting the mitochondrial membrane that powers sperm motility.
While the primary focus is on male effects, some animal studies and traditional uses suggest a potential impact on female reproductive physiology. Research on female rats has indicated that aqueous seed extracts can lead to a reduction in fertility by causing irregular estrous cycles and changes in uterine tissue. This effect is sometimes linked to the compounds potentially mimicking or disrupting reproductive hormones, such as progesterone, which is necessary for maintaining pregnancy.
Safety, Dosage, and Human Data Gaps
Despite the consistent evidence from animal and in vitro studies, there is a significant lack of large-scale, controlled human clinical trials to confirm these effects in people. The antifertility results seen in laboratory settings use highly concentrated extracts, which are substantially different from the small number of seeds a person might consume when eating the fruit. The high doses administered to animals are often orders of magnitude greater than typical dietary intake.
One study did show that aqueous papaya seed extract negatively affected the motility and vitality of human sperm samples incubated in a laboratory setting, confirming a direct biological effect on human cells. This finding suggests a plausible mechanism, yet it does not replicate the complex internal environment of the human body or address safety. The general safety profile in animal studies is often favorable, with no major toxicological effects reported on body weight or vital organs, and the effects on fertility being reversible.
Concerns related to consumption in humans are usually limited to general side effects like digestive irritation or allergic reactions, rather than systemic toxicity or permanent infertility. Given the significant gap in human data and the vast difference between concentrated extracts and dietary amounts, papaya seeds are not a reliable or recommended method of contraception. Therefore, typical consumption of papaya seeds is unlikely to cause infertility, but the concentrated extracts possess a scientifically demonstrated, reversible antifertility potential.