Tea is the most-consumed hot beverage in the world, and the second-most-consumed beverage overall, after water. Herbal tea is a new emerging trend among health-conscious consumers. Herbal tea is made from infusion or by boiling the herbs, spices, or dissolved chemicals from plant material in water to extract the active ingredients.

Since ancient times, people have been using fresh and dried herbs for the preparation of refreshing drinks and medicinal herbal infusions. All models of traditional medicine, such as Ayurveda, Chinese, Unani, Tibetan, Amazonian, and African, integrate phytotherapy into their doctrine, although these are based on different theoretical, cultural, and religious principles. Today, herbal infusions made from any plant part other than the leaves of the tea bush (Camellia sinensis) are known as herbal teas or tisane. Herbal tea includes ingredients that are generally healthy and nutrient rich, and is considered to have several medicinal advantages. It not only provides refreshment but also controls normal physiological processes. Awareness about the benefits of herbal tea is increasing around the world. Also, several global markets are selling customized herbal tea to meet consumer demand.

Market Size & Segmentation
Recent market research reports have shown that the global herbal tea market will grow at a steady pace and will post a moderate CAGR of more than 5% in coming years. Although the brick-and-mortar retail channel remains the key channel in the market, Internet retailing is witnessing rapid growth. Factors such as quick delivery services, uniqueness of profiling, and competitive selling prices are some of the major factors boosting the growth of Internet retailing worldwide.

The herbal tea market is segmented on the basis of raw material, flavor, packaging, product, and region. On the basis of raw material type, the market is segmented as black, green, and yellow tea. Instant pre-mixes, liquid and powdered ready-to-drink (RTD), and syrups are major segments based on product type. Popular flavors often include lemongrass, peppermint, fruit, hibiscus, ginger, and chamomile. Due to intense competition, the commercial success of herbal teas largely depends on flavor.

Health Halo
Herbal teas are becoming increasingly popular due to their diverse biological properties, lack of side effects, and complementary action to modern medicines (see Table 1). Consumer awareness about the potential adverse effects of excessive caffeine intake is also a stimulating factor. Teas prepared from the leaves of the Camellia sinensis plant have about 47 mg of caffeine per cup, while most herbal teas are either caffeine-free or contain trace amounts. Caffeine intake of 6 units/d (>540 mg) during pregnancy is associated with impaired fetal weight and length, whereas the negative effect of excessive intake of caffeine on children is well understood.

The global herbal tea market, based on its beneficial biological properties, is growing side-by-side with the “increasing health and wellness trend which emphasizes the use of natural over synthetic medications for healing of mild disorders such as headaches, colds, digestive problems, etc.” (ACG, 2008). The popularity of herbal tea is increasing globally, especially thanks to antioxidant function. But new research has indicated potential anti-diabetic and anti-obesity activity from many single herb or multi-herb formulations. Some studies have quantified the high amount of polyphenolic compounds in fermented/traditional and unfermented/“green” tea, e.g. rooibos (Aspalathus linearis) and evaluated its cardio-protective effects against ischemia/reperfusion injury in rat models.

Concerns
Certainly, not all herbs are suitable for the preparation of teas, and some plant species may be extremely toxic to humans (e.g., various cultivars of Nerium oleander, which contain cardiac glycosides—oleandrin, oleandroside, nerioside, and digitoxigenin). Although these compounds exert therapeutic effects in a very narrow concentration range, overdosing (unknowingly) with these potent compounds may lead to rapid, and often fatal cardiac failure, and cause problems with the gastrointestinal and central nervous systems.

Another major public health concern is the presence of heavy metal and pesticide contamination in a wide variety of herbal tea products. Several recent publications have highlighted the presence of metallic elements, metalloids, and mineral compounds in herbal teas.

Conclusion
It is well established that the plethora of different polyphenols present in herbal tea synergistically acts together to enhance the antioxidant, anti-diabetic, antimicrobial, and anti-cancer activity of an individual substance (mostly based on in vitro or in vivo studies). The multifunctional effects of combinations include inhibition of inflammatory cytokine production and proteasome activity in cancer cells, induction of apoptosis and essential enzymes such as superoxide dismutase and glutamine synthetase, and epigenetic regulation by affecting DNA methyltransferase.

Since herbal teas are often produced in countries where both soil and air are increasingly contaminated, these products may be tainted with metallic and metalloid elements. But considering the percentage of solubilization in infusions and the bioavailability of each compound, it seems drinking herbal tea does not pose major human health risks. Overall, metallic and metalloid levels in herbal teas studied were in compliance with the maximum permissible limits set by international agencies.

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Dilip Ghosh, PhD, FACN
Nutriconnect

Dilip Ghosh, PhD, FACN, is a director of Nutriconnect (www.nutriconnect.com.au), based in Sydney, Australia. He is also Honorary Ambassador of the Global Harmonization Initiative (GHI) for Australia. Dr. Ghosh received his PhD in biomedical science from University of Calcutta, India & post-doc at HNRCA, Tufts University, Boston. He has been involved in drug-development (synthetic and natural) and functional food research and development both in academic and industry domains. Dr. Ghosh has published more than 90 papers in peer-reviewed journals, books & magazines and he has authored many books, the most recent one, “Pharmaceuticals to Nutraceuticals: A Shift in Disease Prevention,” was published in 2016 by CRC Press, USA. He can be reached at dghosh@optusnet.com.au; dilipghosh@nutriconnect.com.au.