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polyphenols and bone health

Posted Jul 15 2009 8:07pm
This is a very interesting and relevant review by Trzeciakiewicz et in Nutrition Research Review of recent research, which has given insights into dietary components that may optimise bone health and stimulate bone formation.
The vertebrate skeleton is composed of two specialised tissues, cartilage and bone. Bone is essential as its main role is to provide structural support for the body, protect the organs, contribute to haematopoiesis and store minerals. Three distinctly different cell types can be found within bone: the osteoblasts responsible for the synthesis and mineralisation of bone, the osteoclasts implicated in bone tissue resorption and the osteocytes which are the most abundant cells present in the adult skeleton. The integrity of the skeleton requires a dynamic balance between bone formation and bone resorption . If a dysfunction occurs in these two processes, pathologies, such as osteoporosis, can develop.
Fruit and vegetable intake, as well as grains and other plant-derived food, have been associated with decreased risk of major chronic diseases including osteoporosis.This effect has been partially attributed to the polyphenols found in these foods.
Phytochemicals are a large group of plant-derived nonnutritive chemical compounds divided into several classes: phenolics (polyphenols), carotenoids, alkaloids, sterols, terpenes and fibre. Phytochemicals produced by plants are used to protect themselves but recent research demonstrates that certain molecules may protect humans against some pathologies such as cancer, cardiovascular diseases and osteoporosis.
Polyphenols can be divided into different groups depending on the number of phenol rings they contain and on the structural elements bound to these rings. Polyphenols have been classified as phenolic acids, flavonoids, stilbenes, tannins, coumarins and lignans. Among flavonoids, six subclasses exist and share a common structure of two aromatic rings (A and B) bound together by three carbon atoms that form an oxygenated heterocycle (ring C). These are flavones, flavonols, flavanones, isoflavones, flavanols (catechins and proanthocyanidins) and anthocyanidins'F".

Thus, it has been suggested that these compounds may give benefits to bone health through an action on bone cell metabolism. The review shows how some polyphenols can modulate osteoblast function and suggests which cellular signalling pathways are potentially implicated. As yet, few studies have provided clear evidence that phenolic compounds can act on osteoblasts.
Some polyphenols seem to be able to modulate the expression of transcription factors such as runt-related transcription factor-2 (Runx2) and Osterix, NF-KB and activator protein-l (AP-l).
Polyphenols may act on cellular signalling such as mitogen-activated protein kinase (MAPK), bone morphogenetic protein (BMP), oestrogen receptor and osteoprotegerin/receptor activator of NF-KB ligand (OPGIRANKL) and thus may affect osteoblast functions.
Trzeciakiewicz, et al 2009 When nutrition interacts with osteoblast function: molecular mechanisms of polyphenols. Nutrition Research Reviews vol 22 68-81
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