ReviewGreen tea and bone health: Evidence from laboratory studies
Graphical abstract
Introduction
The trend of increased life expectancy is accompanied with an increase in the prevalence of osteoporosis and concomitant complications in the elderly population. Osteoporosis, a degenerative bone disease, is characterized by low bone mass and microstructural deterioration of bone tissue that results in bone fragility and an increased susceptibility to fractures [1]. Hip fracture is the most severe consequence of osteoporosis, resulting in decreased activities of daily living, lowered quality of life, and increased mortality [2].
Osteoporosis occurring in postmenopausal women and elderly men represents a major health and economic burden in our fast growing elderly population. In the United States, approximately 44 million or 55 percent of the people 50 and older have osteoporosis or low bone mass [3]. It is estimated that by 2020, there will be over 61 million women and men in this age category that are affected [3]. By the year 2025, experts predict that the costs of osteoporosis-related expenses will rise to approximately $25.3 billion [4].
Although there are a variety of agents available for the prevention and/or treatment of low bone mass (also called osteopenia) and osteoporosis, some patients select complementary and alternative therapies, such as dietary supplements or functional foods, for this purpose [5]. Tea, the dried leaves of the Camellia sinensis species of the Theaceae family, is a popular beverage with an annual production of three billion kilograms worldwide [6]. In the past decade, epidemiological evidence has shown an association between tea consumption and the prevention of age-related bone loss in the elderly population. The impact of tea consumption on bone mass and risk of osteoporotic fractures in humans has been comprehensively reported in our previous review paper and we found that among different forms of tea (green tea, black tea, white tea, and Oolong tea), drinking green tea and/or ingesting green tea bioactive compounds may mitigate bone loss in elderly women and men, thereby decreasing their risk of osteoporotic fractures [7]. Therefore, in this review, we focus on animal studies in various models with an emphasis on bone health. In addition, a short-term translational study employing green tea supplement given to postmenopausal women with low bone mass is also discussed.
Section snippets
Bone biology and metabolic disorders
Bone is a highly specialized support tissue which is characterized by its rigidity and hardness. As a material, bone has strength similar to cast iron, while its density is as low as wood. Calcium and phosphorus mineral crystals are deposited around the protein strands. The flexible protein strands provide the tensile strength that holds the structure together and the brittle minerals provide the solid structure. The two main categories of bone cells are osteoblasts that form the bone and
Evidence of osteo-protective effects of green tea in animals
All but one animal studies support that green tea may benefit bone health by mitigating bone loss due to aging, aging plus sexual hormone deficiency, or chronic inflammation, or by preserving bone mass due to obesity, as summarized in Table 1.
Implication of green tea's osteo-protective effect in humans
In addition to the animal studies, the findings of our short-term 6-month clinical trial indicated that the consumption of GTP (500 mg per day) by postmenopausal women appeared to be safe, particularly in terms of liver and kidney functions [32]. In that study, 171 postmenopausal women with low bone mass (57.4 ± 6.8 yr, BMI 28.4 ± 5.3 kg/m2) were randomly assigned into 4 treatment groups for 24 weeks: (1) Placebo (500 mg medicinal starch/day), (2) GTP (500 mg GTP/day), (3) Placebo + Tai Chi (placebo plus
Mechanisms of action
Numerous studies have indicated that excessive oxidative stress is a pivotal pathogenic factor [33] for age-related bone loss in mice [34], rats [16], and the elderly population [35], [36] resulting in increased osteoblast and osteocyte apoptosis, and decreased osteoblast population and bone formation rate [34]. Oxidative stress suppresses osteoblastic differentiation [37], [38] via extracellular signal-regulated kinases (ERK) and ERK-dependent NF-κB signaling pathways [39]. Osteoblasts can
Summary and future research
Osteoporosis is the result of a metabolic imbalance of faster resorption than formation. To date our animal studies strongly suggest that green tea has a pronounced effect on bone in terms of bone preservation as shown by higher bone mass (BMC and BMD), trabecular bone volume, number, and thickness, and lower trabecular separation through enhancing bone formation and suppressing bone resorption, resulting in greater bone strength. Although these results are mostly obtained from rat studies, we
Acknowledgment
The preparation of this review was supported by NIH/NCCAM grant R21AT003735, Laura W. Bush Institute for Women's Health, and Winthrop-University Hospital.
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2020, Trends in BiotechnologyCitation Excerpt :Experimental and population-based studies have demonstrated the efficacy of green tea against osteoporosis [24]. Green tea has been demonstrated to inhibit bone resorption and stimulate osteoblast activity [25–27]. The efficacy of green tea in the prevention of age-related bone loss activity has also been considered in various studies.
Estrogenic biological activity and underlying molecular mechanisms of green tea constituents
2020, Trends in Food Science and TechnologyCitation Excerpt :The health-promoting properties of tea have long been known because it was used to treat patients with infectious diseases (Weisburger, 1997). Recent studies suggested that green tea has, to some extent, beneficial effects on cardioprotection (Hodgson & Croft, 2010), cancer chemoprevention (Khan, Siddiqui, Adhami, & Mukhtar, 2013), adjusting the intestinal microflora (Okubo & Juneja, 1997), protecting the internal and other organs (such as kidneys, bone and muscle) (Bao & Peng, 2016; Buetler, Renard, Offord, Schneider, & Ruegg, 2002; Shen, Yeh, Cao, Chyu, & Wang, 2011), and strengthening the immune system (Bukowski, 2013), and if can be used as remedy for allergies (Maeda-Yamamoto et al., 2009), diarrhea (Ishihara & Akachi, 1997), and obesity/diabetes (Nagao et al., 2009) or in cosmetics for hair/oral care (Khurshid, Zafar, Zohaib, Najeeb, & Naseem, 2016; Kwon et al., 2007) and deodorizers (Yasuda & Arakawa, 1995). Epidemiological and intervention studies of green tea demonstrated that catechins are effective against certain types of cancer such as prostate, breast, lung, liver and digestive tract cancers (Khan et al., 2013).
Aspalathin from Aspalathus linearis (rooibos) reduces osteoclast activity and increases osteoblast activity in vitro
2020, Journal of Functional FoodsCitation Excerpt :A recent study in rats showed that aspalathin-enriched green rooibos extract could possess insulin sensitising effects (Mazibuko-Mbeje et al., 2019). Many of these effects may be attributed to the known effects of aqueous rooibos extract on the NFκB pathway (Shen et al., 2011). In our laboratories, aqueous rooibos tea extract has been shown to inhibit osteoclast differentiation and bone resorption in an in vitro study using RAW264.7 murine macrophage-derived osteoclasts (Moosa et al., 2018).
Tea polysaccharide inhibits RANKL-induced osteoclastogenesis in RAW264.7 cells and ameliorates ovariectomy-induced osteoporosis in rats
2018, Biomedicine and PharmacotherapyCitation Excerpt :RANKL plays an important part in the development and function of osteoclasts [40]. Emerging evidence indicates that the bioactive constituents found in tea may improve bone metabolism by enhancing osteoblast differentiation and suppressing osteoclast formation and differentiation [17,18]. We found that TPS inhibited RANKL-induced osteoclast differentiation significantly in a dose-dependent manner, and that the inhibitory effect of TPS was not due to its toxic effect on RAW264.7 cells (Fig. 1).
A Meta-Analysis on the Association between Tea Consumption and the Risk of Osteoporotic Fractures
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