In Nutrition Research Review 2007 , 20, 89-105, T. P. Dew.et al write on Bone mineral density, polyphenols and caffeine: a reassessment
In an ageing society, the maintenance of good bone health with age is important. In osteoporosis, bone becomes increasingly porous, resulting in both greater chance and severity of bone fracture at the hip. spine, forearm and shoulder. Bone fractures result in reduced mobility, discomfort and a higher risk of early mortality. Osteoporosis can cost the UK over £1-7 billion for the treatment of hip fracture.
Elderly women are at risk from osteoporosis, because they can lose between 10 and 15 % of their bone every decade after the menopause. Women lend to have lower peak bone mass than men, and that levels of oestrogen (a hormone with a positive effect on bone health) are decreased during and after menopause and tend to live longer than men.
Bone tissue is in a constant state of flux. The skeleton has obvious mechanical roles and is also a Calcium depository for the rest of the body, with calcium being removed and replaced as required. The state of bone flux within an individual can be described in terms of bone mineral density. Bone metabolism is controlled by a variety of growth hormones, sex steroid hormones (such as oestrogens), thyroxine. corticosteroids and insulin. Three hormones play vital roles, 1.25-dihydroxycholecalciferol. parathyroid hormone and calcitonin. As well as affecting dietary calcium adsorption efficiencies, these hormones also influence the three cell types relevant to bone formation and metabolism osteoblasts (hone formation), osteocytes (bone maintenance) and osteoclasts (bone resorption). The balance between the formation and resorption of bone tissue is affected by genetic and environmental (for example, diet and lifestyle) factors.
Several studies have shown benefit from drinking tea and bone mineral density and fracture risk. This could be due to the fluoride and polyphenol components of tea. Caffeine consumption has been sen as a potential risk factor for low bone mass density and high fracture risk.
Fruit and vegetable intake which includes increased polyphenols intake may also contribute positively to bone health.
In this review the evidence surrounding the function(s) of poly phenol-rich foods in bone health is examined, along with more recent studies challenging the relevance of caffeine consumption to in vivo Ca balance. Plant foods rich in polyphenols such as tea. fruit and vegetables, as significant factors in a healthy diet and lifestyle, may have positive rules in bone health, and the negative role of caffeine may have been overestimated.

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