American palm ethnomedicine: A meta-analysis

We found reports of medicinal uses for 106 American palm species (see Additional File 1). The most commonly used were: Cocos nucifera, for 19 different medicinal use categories, Oenocarpus bataua, for 14 categories; and Euterpe precatoria, for 14 categories (Fig. 2). Cocos nucifera is commonly cultivated throughout the Americas and was most likely introduced from other countries; in contrast, O. bataua and E. precatoria are native to the tropical rainforests of the Amazon basin and adjacent regions. The next most commonly used species was Attalea speciosa (13 categories). Phoenix dactylifera, Euterpe oleracea, Attalea phalerata, Phytelephas macrocarpa, Bactris gasipaes, Acrocomia aculeata, and Socratea exorrhiza were employed in 9-12 different medicinal use categories. Among American indigenous peoples, the best-known ethnomedicinal palms are the native palms, O. bataua, S. exorrhiza, E. precatoria, and a species with unknown origin, C. nucifera [1]. C. nucifera is widely cultivated throughout the tropical areas of the world. Thus, medicinal use of C. nucifera is the most widespread of the palms in the Americas (Fig. 2).

The fruit of the palm is most commonly used for medicinal purposes; the fruit is used in 56 species, the oil is used in 19 species, the mesocarp in 16 species, and the endosperm in 11 species. Other parts of the palms that are used include roots (27 spp.), leaves (22 spp.), palm hearts (19 spp.), stems (17 spp.), and flowers (9 spp.). Often, several species in the same genus are used medicinally (Fig. 3). For example, the genus Attalea has 11 different species with medicinal uses; the genera Astrocaryum, Bactris, and Syagrus each have 10 medicinal species; and the genus Geonoma has seven medicinal species; all the other genera have 1-5 species that are used medicinally. As expected, species from the same genus often have similar uses [9] but there are exceptions to this rule; O. bataua prevents fever, but Oenocarpus bacaba can be harmful to a person recovering from intermittent fever [10, 11].

Obviously, most medicinal uses of palms are beneficial; but, like many other drugs, inappropriate use may be harmful. For instance, a beverage made of O. bataua fruit is said to quickly cause a "horrible death" when mixed with liver of tapir [12]. The prevalence of medicinal palm use is notable; for example, the roots of E. precatoria are used medicinally almost everywhere it grows [10, 13‐19].

In a general ethnomedicinal study of indigenous communities in Mexico, the most frequent ailments treated with medicinal plants were gastrointestinal disorders, dermatological diseases, and respiratory disorders [20]. These categories were also confirmed by other authors [21‐23] that studied ethnomedicines in the indigenous societies of the Americas. In this paper, we used a different classification of diseases [8] (Fig. 4); our data related mainly to indigenous, but also to some non-indigenous peoples; and we looked only at health conditions treated with medicines from a single plant family. Among the diseases treated by palms, digestive system disorders were frequent, but pain ailments and skin tissue disorders were even more frequent. The preponderance of pain, injuries, and muscular-skeletal system disorders that could be treated with palm medicines may have reflected the epidemiological characteristics of the indigenous peoples in the region. Some indigenous peoples live in a traditional way, where hunting and gathering play a considerable role in subsistence. Hence, injuries and muscular-skeletal system disorders may be directly connected to everyday hunting activities. Palm-derived remedies may provide emergency treatments, as they commonly grow around villages and are easily accessible. Emergency medicines derived from palms, particularly those with styptic properties, like those derived from A. speciosa, are commonly used by the Apinayé and Guajajara Indians of northeastern Brazil [12]. Among the Warao and Arawak of Guyana, E. oleracea is considered a useful hemostatic medicine when a person is injured deep in the forest [24]; the sap of Euterpe edulis also possesses hemostatic properties [25].

Circulatory system disorders are among the major health problems in Western civilization; however, these seem not to be important among peoples that use American ethnomedicines derived from palms. Similarly, there are almost no reports of neurological system disorders that are common among ageing Western societies.

Palm medicines also have an indirect influence human health. Beetle larvae that live in the decaying stems of Astrocaryum chambira, Wettinia maynensis [26], A. phalerata, and O. bataua are collected and used in medicines to cure severe chest pains [27‐29]. A fungus that causes chromoblastomycosis has been found in the shell of A. speciosa, which may explain the prevalence of this disease among farm workers in the Amazon region of Maranhao in Brazil [30]. Problems with Triatominae infested palms are common in many places [31‐41]. Most Rhodonius sp. (Hemiptera, Reduviidae, Triatominae) are associated with palm trees; they transmit Trypanosoma cruzi, the organism responsible for Chagas disease throughout the American tropics [42].

Traditional medicines of American peoples are also used to treat some folk illnesses like susto - bad spirit. Folk illnesses form part of the broader indigenous world-view, and there are no direct equivalents in modern medicine nomenclature. From the medical point of view, folk illnesses are not diseases sensu stricto, but clusters of loosely bound syndromes. Consequently, in the category of Social Uses for palm medicines, we included uses connected to healing rituals and folk illnesses.

As mentioned above, previous knowledge about the ethnomedicinal uses of American palms was based primarily on local knowledge and ethnobotanical studies [25]; in contrast, many recent papers have investigated the phytochemical and pharmacological bases for ethnomedicinal treatments. We compared local rationale and pharmacological evidence in a number of cases where both kinds of evidence existed.

There are many, often conflicting, reports about the medicinal properties of A. speciosa (babassu). Mesocarp flour from its fruit is used in Brazil to treat pain, constipation, obesity, leukemia, rheumatism, tumors, and ulcerations (references in Additional File 1). It has also been shown to have anti-inflammatory [43] or pro-inflammatory [44] properties, depending on the inflammation model and the time or route of treatment. These reports, together with the fact that it is used to treat venous disease, suggest that it could be a good candidate for the development of new medicines [45]. However, when tested, extracts of its leaves, flowers, and endocarp did not show pharmacological activity [46]. This may suggest that the uses are based on physiological effects of the mesocarp, which may have properties not found in other parts of babassu palm.

Interestingly, sap from the stem of E. oleracea (açai) is used as a hemostatic agent among Matowai, Arawak, and Warao peoples; however, pharmacological studies indicated that the fruit stone extract of E. oleracea had a vasodilator effect [47]. The fruit of E. oleracea also holds promise for use in modern medicine as an alternative oral contrasting agent for MRI (Magnetic Resonance Imaging) studies of the gastrointestinal system [48].

The traditional claim that roots of E. precatoria have anti-inflammatory activity appears to have been verified, although the mechanism that underlies the effect remains unknown [19].

The roots of E. precatoria and the fruits of O. bataua were traditionally and are presently used to treat malaria in Peru [[15], Rengifo 2007, and Agencia Española de Cooperación Internacional para el Desarollo 2007 personal communication]. Although Deharo et al. (2001) [49] did not include these species in their pharmacological tests of anti-malarial activity, other studies showed a moderate antiplasmodial activity in extracts of E. precatoria roots [50].

In ethnobotanical studies, the fruit extracts of Astrocaryum vulgare and A. speciosa have been reported to be useful for the treatment of skin diseases. However, when they were screened for anti-tyrosinase activity, the effect was poor [51].

Hypoglycemic compounds have been found in the roots of A. aculeata in many studies; this coincides well with its traditional use as a treatment for diabetes among indigenous peoples in Mexico [52‐54].

Coconut (C. nucifera) oil was shown to have antiseptic effects and is used as an efficient, safe skin moisturizer [55]. This suggested that its traditional use as a lotion in many parts of America is well founded. Its selective antibacterial effects [56] also make it useful for topical applications in wound healing. Other studies have suggested that extracts from C. nucifera husk fibers could be useful in the treatment of leishmaniasis [57, 58]. In traditional Mexican medicine, C. nucifera has been used to treat trichomoniasis, dysentery, and enteropathogens. These uses are consistent with its antimicrobial effects. Moreover, recent pharmacological studies have demonstrated that extracts of C. nucifera could be used as an alternative method to treat drug resistant enteric infections [59, 60]. In vivo assays demonstrated that C. nucifera extract had low toxicity, and that it did not induce dermic or ocular reactions [57]. Thus, considering its potent antioxidant activity and low toxicity, husk fiber extracts of C. nucifera have potential in the treatment of oral diseases [61]. Furthermore, its aqueous extract may be a source of new drugs with anti-neoplastic and anti-multidrug resistance activities [62]. It is of great interest for cancer therapy to identify new compounds that are able to overcome resistance mechanisms and lead to tumor cell death.

Seeds of Aiphanes aculeata were traditionally used for treatment of cancer by people from the Peruvian Amazon region (Rengifo, personal communication, 2007). Lee et al. (2001) [63] isolated Aiphanol and some other compounds that may have chemopreventive properties, but they have not been pharmacologically tested for their effects on cancer.

Increasing attention has focused on the use of phytotherapeutic agents to treat prostate disorders, ranging from benign prostatic hyperplasia to prostate cancer. The best described phytotherapeutic agent for prostate disorders was from Serenoa repens (saw palmetto) [[64‐68], among others]. Several studies have reported no side effects of saw palmetto treatments [69], and a dietary supplement with S. repens may be effective in controlling prostate cancer tumorigenesis [70]. The extract of S. repens was as effective as the tested pharmaceuticals in the relief of urinary symptoms [71, 72]. The roots of Roystonea regia are used as a traditional medicine in Eastern Cuba to cure impotence [73]. Currently, R. regia fruit lipid extracts are being tested in the Cuban National Center for Scientific Research, and preliminary results suggest that they appear to provide a promising treatment for prostatic hyperplasia [74‐82].