Table 2.

Beneficial effects of natural antioxidants on bone metabolism.

Natural Compound	Source	Molecular Structure	Bone Effects	Ref.
Anthocyanins	Blueberries, bilberries, vegetables, cereals, dry legumes, chocolate, tea, coffee, wine		-antioxidant effect -increase in osteoblast and inhibition of osteoclast activity -prevention of bone loss in OVX-induced osteoporosis -prevention of macrophage differentiation into osteoclasts -promotion of bone growth	[35,38,91,97,98,101,127] [35,95,97,100,126] [98,126,128,129,130,132] [134,135,136] [5,97,98,102,128]
Phlorizidin	Apple		-inhibition of bone loss and preservation of total and metaphyseal BMD in OVX rats with and without inflammation	[137]
Phloretin	Apple		-antioxidant activity and promotion of osteoclast apoptosis in murine macrophages -promotion of osteoblast activity	[138] [139]
Epigallocatechin gallate	Green tea		-antioxidant activity, inhibition of osteoclastogenesis, and protection from OS inhibition of osteoblast differentiation -increase in bone volume and improvement of its mechanical properties -increase in expression of osteocalcin and collagen 1α1 -protection from glucocorticoid-induced osteoporosis	[142,143,146,147,148] [144] [148] [146]
Theaflavin-3,3′-digallate	Black tea		-antioxidant and anti-inflammatory action -decrease in osteoclast differentiation and promotion of the expression of osteogenic markers under an inflammatory environment	[149,151] [150,151]
Genistein	Soy		-antioxidant and anti-osteoporotic activity	[109,154]
Curcumin	Turmeric plant		-antiapoptotic effect on osteoblasts, inhibition of osteoclastogenesis and activation of osteoclast autophagy -modulation of BMD in postmenopausal women with osteoporosis -protection from glucocorticoid-induced osteoporosis	[156,157,158] [157] [155]
Anacardic acid	Cashew nut		-attenuation of osteoclastogenesis and improvement of BMD in OVX murine model	[159]
Resveratrol	Grapes, wine, grape juice, Itadori tea, peanuts, cocoa, blueberries, bilberries, cranberries		-antioxidant activity and promotion of osteogenesis -increase in bone mineral density in osteoporotic obese men -protection from estrogen deficiency and dexamethasone-induced osteoporosis in rats -beneficial effects on bone density in lumbar spine and neck of femur in postmenopausal women	[162,163,164] [160] [165,166,167] [168]
Tannins	Grape seeds		-protection of osteoblasts from glucocorticoid-induced oxidative stress -inhibition of bone marrow macrophages differentiation into osteoclasts -improvement of bone loss in ovariectomized animals	[173] [174] [171,172]
Ferulic acid	Fruits		-protection from dexamethasone-induced osteoporosis	[175]
Oleuropein, hydroxytyrosol, tyrosol	Olive oil		-antioxidant and anti-inflammatory effect, and prevention of bone loss -improvement of calcium homeostasis for bone health maintenance and bone growth	[179,180,181] [181,182]
Lycopene	Tomatoes		-antioxidant effect -decrease in osteoclast differentiation and increase in osteoblast activity -prevention of bone loss and reduction of osteoporotic fractures	[187,188,189,190] [191] [192,193]
Vitamin C	Fruits and vegetables		-inhibition of osteoclast activity, stimulation of osteoblast maturation, and positive effect on BMD	[194]
Vitamin E	Fruits, vegetables, seeds		-antioxidant and anti-inflammatory effect -prevention of bone loss and induction of bone formation -preservation and maintenance of bone mass in premenopausal women	[195,198,199] [196,197,198,199] [197]
Glutathione	Intracellular		-antioxidant effect -inhibition of osteoclast activation, activation of osteoblast differentiation, and mineralization process -prevention of osteocyte apoptosis	[13,14,15,17,18] [17,202] [51]
Alpha lipoic acid	Intracellular, vegetables, red meat		-antioxidant effect and decrease of inflammatory cytokines -prevention of osteocyte apoptosis and increase in osteoclastogenic factors -increase in BMD levels and promotion of osteogenesis in glucocorticoid-induced osteoporosis	[51,205,206] [51] [204,205]