Green tea may protect women from osteoporosis. (Photo by René Ehrhardt)
Osteoporosis is a common problem in middle-aged women. It is characterized by a thinning of bones and increased fracture risk. While it's common for bones to lose some of their strength with age, menopause adds considerably to the problem. This is thought to be due to an insufficiency in estrogen levels after menopause.
According to a paper by Shen et al., green tea may be effective in preventing bone loss associated with age and estrogen deficiency. They fed green tea to ovariectomized (which means the surgical removal of ovaries) and aged rats and noticed that their bones were in better shape than those of rats fed with water. Ovariectomized rats are often used as an animal model of postmenopausal osteoporosis. These rats are deficient in estrogen and have an increased bone loss similar to women after menopause.
The female rats were first divided into two groups: the non-ovariectomized ("premenopausal") and ovariectomized ("postmenopausal") group. Each group was given water only or green tea polyphenols mixed with drinking water in a 0.1% or 0.5% concentration. The purity of the polyphenol extract was higher than 80%, meaning that at least 80% of the content was catechins. Once again, the most abundant catechin was epigallocatechin gallate (EGCG).
Green tea and bone loss in non-ovariectomized ("premenopausal") female rats
After 16 weeks, the water-only control group had lost a significant amount of bone mineral content (BMC) compared to baseline (408 --> 382 mg). The loss of bone mineral content in the 0.1% green tea polyphenol (GTP) group was not statistically significant compared to baseline (408 --> 403 mg) but was significant compared to the control group (403 vs. 382 mg).
The 0.5% GTP group actually had an increase in bone mineral content compared to baseline (408 --> 417 mg), but this was not statistically significant. Compared to the loss seen in the control group (408 vs. 382 mg), however, the difference was statistically significant.
Bone mineral density (BMD) also significantly decreased in the control group (243 --> 228 mg/cm^2). The 0.1% GTP rats lost less bone mineral density (243 --> 236 mg/cm^2) than the control group, while the 0.5% GTP retained their BMD.
Green tea and bone loss in ovariectomized ("postmenopausal") female rats
Unsurprisingly, the ovariectomized rats lost even more BMC than the non-ovariectomized rats. The decrease was greatest in the control rats (408 --> 339 mg). This time green tea polyphenols in drinking water failed to significantly slow the loss. In the 0.1% GTP group, the loss was slightly greater (408 --> 347 mg) than in the 0.5% GTP group (408 --> 352 mg), but the difference was not statistically significant.
BMD also decreased more than in the non-ovariectomized rats, with the control group showing the biggest loss (243 --> 198 mg/cm^2). Compared to the control group, the 0.1% GTP group retained significantly more bone mineral density (204 vs. 198 mg/cm^2), as did the 0.5% GTP group (206 vs 198 mg/cm^2).
Estrogen deficiency and aging together resulted in a greater loss of bone mineral content and bone mineral density in female rats than aging alone. Green tea polyphenols attenuated the loss in a dose-dependent manner. The protective effect of green tea was greater in female rats without estrogen deficiency.
Green tea extract was given to rats in a 0.1% or 0.5% concentration (>80% catechin content) in drinking water. According to the authors, this is equivalent to 1 and 4 cups of green tea in humans, respectively.
For more information on green tea, see these posts:
Green Tea Protects from Arthritis in Rats
Vitamin C Protects Green Tea Catechins from Degradation
Green Tea Protects Cartilage from Arthritis in Vitro
Green Tea Extract Enhances Abdominal Fat Loss from Exercise