Elsevier

Pharmacological Research

Volume 64, Issue 2, August 2011, Pages 155-161
Pharmacological Research

Review
Green tea and bone health: Evidence from laboratory studies

https://doi.org/10.1016/j.phrs.2011.03.012Get rights and content

Abstract

Osteoporosis is a major health problem in the elderly. Epidemiological evidence has shown an association between tea consumption and the prevention of bone loss in the elderly population. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea with its bioactive components on bone health with an emphasis on the following: (i) the etiology of osteoporosis, (ii) evidence of osteo-protective impacts of green tea on bone mass and microarchitecture in various bone loss models in which induced by aging, sex hormone deficiency, and chronic inflammation, (iii) discussion of impacts of green tea on bone mass in two obesity models, (iv) observation of short-term green tea supplementation given to postmenopausal women with low bone mass, (v) possible mechanisms for the osteo-protective effects of green tea bioactive compounds, and (vi) a summary and future research direction of green tea and bone health.

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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