Review of Scientific Research on Swallow Birds Nest

Swallow Birds Nest is one of the widely used health foods in Chinese communities. The market generated by it is increasing because it exhibits a lot of beneficial effects to human beings. For its high market value, fake Swallow Birds Nest and misleading promotional description emerged. This article briefly reviews the scientific research on authentication technologies and pharmacological effects of Swallow Birds Nest. It is expected that people’s knowledge on Swallow Birds Nest could be enhanced.

Background

Swiftlets (collocaliini) are tiny insectivorous birds that are distributed from the Indian Ocean , through Southeast Asia and North Australia to the Pacific[1]. Amongst various species of swiftlets in the genus of Collocalia, only the nests of four species habituating in the Southeast Asian region have commercial value because of human consumption. They are Collocalia fuciphaga, Collocalia germanis, Collocalia maxima and Collocalia unicolor[2]. Collocalia species, average 6.5g in weight, have glossy plumage[1]. Their nests are constructed with salivary glue, a cementing substance, and may incorporate other materials such as vegetation or feathers. It takes about 20 days to finish the nest. The Swallow Birds Nest ( 燕窩 in Chinese) making up with purely salivary glue are much more expensive than those incorporating with other materials (see Figure 1 in p.40).

In Hong Kong and in Chinese societies throughout the world, traditional Chinese medicine (TCM) is commonly used to treat diseases and enhance health. It is believed that TCM herbs have wide-ranging effects for enhancing health, lowering risk of diseases and promoting life span [3,4,5]. Being one of the TCMs, Swallow Birds Nest is believed to have health enhancing effects such as anti-ageing, growth promoting and immunoenhancing properties. In fact, the medicinal use of Swallow Birds Nest can be traced back to 17th century[6]. However, Swallow Birds Nest is different from most of the TCMs. It is not only a medicine to make people healthy but also a pleasant food. Traditionally, it is double boiled with rocky sugar to make a delicacy known as “Swallow Birds Nest”.

Although the size of Collocalia is small, the market generated by it is tremendous. The estimated market of Swallow Birds Nest in 2004 is worth about HK$ 3 billions in Hong Kong . The local market is the world’s largest consumer of Swallow Birds Nest[2,7]. The annual percentage increase of the local market is in doubledigit[7]. It may be due to the fact that Hong Kong people are more and more concerned about their health and the status of TCM has risen after a series of government policies on TCM. Moreover, a dual nature of Swallow Birds Nest, that could be treated as medicine or/and food, may play a role. In the past, people could only buy dried Swallow Birds Nests. For the advancement in food technology, large variety of Swallow Birds Nest related products emerge to the market. They are readily to serve products. No cooking process is required. Amongst those new products, most of them are still in the traditional form as Swallow Birds Nest, such as instant Swallow Birds Nest in different concentrations. Some instant Swallow Birds Nest may also supplement with other TCMs. Apart from the traditional form, there is a trend of using Swallow Birds Nest extract as one of the chief ingredients of the products. These products focus mainly on the medicinal use of Swallow Birds Nest. However, some of them may exaggerate the therapeutic use of Swallow Birds Nest. For the limited supply and high price of Swallow Birds Nest, it is not uncommon to hear reports of fake Swallow Birds Nest in the market. The imitation substitute commonly used is the edible plant-exude, gum karaya or sterculia[8]. Recently, there are reports of fake Swallow Birds Nest made from fishes’ skin, mushroom or algae in China [9]. Therefore, it is a great concern on authenticating the genuineness of Swallow Birds Nest. In this review, the author will briefly summarize some advanced technologies in authenticating Swallow Birds Nest. The medicinal benefits of Swallow Birds Nest with contemporary scientific evidence will also be given.

Review of Scientific Research on Swallow Birds Nest

Authenticity of Swallow Birds Nest

The first comprehensive report on authentication of Swallow Birds Nest can be traced back to the early 1990s. Sam et al., (1991) demonstrated the possibility to use scanning electron microscopy, energy dispersive X-ray microanalysis, flame atomic emission spectroscopy, inductively coupled plasma-atomic emission spectroscopy, ultraviolet-visible spectroscopy and other physico-chemical techniques to ascertain the authenticity of Swallow Birds Nest[8]. Since they only made a comparison with some imitation Swallow Birds Nest with substances from plant origins, it limited the generalizing ability of the techniques to other imitation materials. In addition, they relied on sophisticated equipment. It is hard for commercial testing laboratories to carry out. Recently, a research team in China has developed a simple but accurate and reliable spectrophotometry method to determine Swallow Birds Nest content[10]. It could also be used to differentiate genuine Swallow Birds Nest with saliva, pig’s skin and Tremella fucifomis[10]. The method is based on the reaction between N-acetylneuramic acid and ninhydrin in acid solution. The method evaluates the internal content of N-acetylneuramic acid, a nine-carbon sugars, which is one of the major components in Swallow Birds Nest.

Nutritional Content and Medicinal Use

Swallow Birds Nest contains mainly carbohydrates, amino acids and mineral salts. The major ingredients of Swallow Birds Nest are glycoproteins[11]. Amongst the carbohydrates in Swallow Birds Nest, sialic acid (9%) is the major one. It was found that exogenous source of sialic acid may contribute to neurological and intellectual advantages in infants[12]. However, the nutritional and biological mechanisms of sialic acid in human body are still under investigation. The other major carbohydrates include 7.2% galactosamine, 5.3% glucosamine, 16.9% galactose and 0.7% fucose[11].

Amino acids and mineral salts are also important components in Swallow Birds Nest. Three non-essential amino acids (aspartic acid, glutamic acid, praline) and two essential amino acids (threonine and valine) can be found[11]. They could facilitate normal body functions such as repairing and immunity. Swallow Birds Nest is rich in mineral salts. It contains high content of sodium and calcium. It is because the source of Swallow Birds Nest is derived from saliva Collocalia inhabiting mainly in limestone caves. In addition, low levels of magnesium, zinc, manganese and iron are also detected in Swallow Birds Nest[8].

In spite of the long history of using Swallow Birds Nest for medicinal purposes, there are not many scientific researches related to the therapeutic use of it in literature. The first scientific evidence was given by Ng et al. (1986) in Hong Kong. Swallow Birds Nest aqueous extract was found to potentiate mitogenic response of human peripheral blood monocytes to stimulation with proliferative agents, Concanavalin A and Phytohemagglutinin A[13]. It suggested that Swallow Birds Nest might possess immunoenhancing effect by aiding cell division of immune cells.

One year later, other scientific evidence was published by Kong et al. They demonstrated an epidermal growth factor (EGF)-like activity in aqueous extract of Swallow Birds Nest that stimulated the DNA synthesis in 3T3 fibroblast in a dose dependent manner in vitro[6]. EGF is a 6,000 Da polypeptide hormone produced by glands of the gastrointestinal tract, namely the salivary and Brunner’s glands. It appears to play a crucial role in major normal cellular processes such as proliferation, differentiation and development[14]. It may offer a rationale for the medicinal use of Swallow Birds Nest in ageing resistance. Since the receptor for EGF is highly expressed in a number of solid tumors, including breast, head-and-neck, non-small-cell lung, renal, ovarian and colon cancer[15], people are worried about a possibility to induce tumor progression and to resist chemotherapy/radiation treatment in tumor cells; in consequence, suggest that cancer patients should avoid Swallow Birds Nest. In fact, there is no evidence supporting this suggestion. Currently we have evaluated the effects of aqueous extract of Swallow Birds Nest on the viability on two human cancer cell lines, human breast cancer MCF-7 (ATCC HTB-22) and human liver cancer HepG2 (ATCC HB-8065). There was no observable effect on cell viability when comparing with the control group (unpublished data).

In 1994, a research team in China, evaluated the pharmacological effects of Swallow Birds Nest and pearl powder containing formulation. The formulation was demonstrated to have immunoenhancing effects by elevating DNA synthesis of T-lymphacytes and circulating immunoglobulin M content in mice. In addition, the formulation also showed ageing retardation by increasing the level of superoxide dimutase[16]. However, the study did not explore whether the effects came from either Swallow Birds Nest, pearl powder or both.

Further Studies

Swallow Birds Nest has been used for several hundred years. Its usage is based mainly on historical, anecdotal and observational reports of its benefit. Scientific evidence for its efficacy is still limited. The putative health benefits such as resisting ageing and improving immunity of Swallow Birds Nest may be linked, at least in part, to EGF-like activity and mitogenic factor. However, there may be other mechanisms involved. In addition, there may be additive, synergistic or antagonistic effects between different components of Swallow Birds Nest. Work is needed to establish health-related effects of Swallow Birds Nest, for example, through assessing biomarker response, isolating and identifying the active components and investigating their possible interaction. In Hong Kong, many people take Swallow Birds Nest regularly. It is worth establishing epidemiological study to measure relationship of consistent use of Swallow Birds Nest and its putative beneficial effects in human beings. For the large market of Swallow Birds Nest, developing a systematic method to identify the sources of Swallow Birds Nest and check the authenticity of its sample is, undoubtedly, indispensable.

Acknowledgements

The author is grateful to Imperial Swallow Birds Nest International Company Limited for providing intact Swallow Birds Nests and their photos. Special thanks go to Ms. Siu-Hung Tsui for editorial assistance.

References

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