Reviewed: Wu C, Yang Y, Yao W, Lu F, Wu J, Chang C. Epidemiological evidence of increased bone mineral. Archives of Internal Medicine 2002;162:1001-1007.
After water, tea (Camellia sinensis (L.) Kuntze, Theaceae) is the most common, regularly consumed beverage in the world. It is categorized into three types: green (nonfermented), oolong (partially fermented), and black (fermented). Tea contains several hundred compounds that may affect the body. According to epidemiological studies, the evidence strongly suggests that tea (particularly green tea) may prevent cardiovascular disease, atherosclerosis, and some types of cancer; however, information about the effects of tea consumption on bone mineral density (BMD) is limited. This study sought to answer:
1) Is there relationship between tea consumption and BMD?
2) Is there a dose-response effect? and
3) Which characteristics of tea consumption influence BMD?
This prospective epidemiological survey of chronic disease in Tainan, Taiwan included a total of 1,037 subjects (497 men and 540 women), 30 years or older in the final analysis. Subjects were questioned on their lifestyle and tea consumption, and had BMD screening of total body, lumbar spine (L1-L4), hip neck, and Ward's triangle (a specific region of the hip bone, or femur, within the narrowest part of the hip).
There was a positive correlation between duration of habitual tea consumption and BMD in the four body regions. Five hundred and two subjects (48.4 percent) were habitual tea drinkers, with a mean duration of tea consumption of approximately 10 years. Compared with nonhabitual tea drinkers, subjects with habitual tea consumption of 6-10 years showed higher lumbar spine BMDs when compared to nonhabitual tea drinkers, and those with consumption of more than 10 years showed the highest BMDs in all measured regions. There was no significant difference in BMD between habitual tea drinkers with 1 to 5 years' duration and nonhabitual tea drinkers. Men had higher BMDs than women, and BMD decreased with age for both genders. Total physical activity also had a positive effect on BMD of the total body, hip, and neck. After adjustment for all covariants, no significant differences of BMD could be found between those who drank green or oolong tea compared with those who drank black tea.
Consistent with other findings, tea had a protective effect on BMD of the total body, lumbar spine, and hip regions. To the authors' knowledge, this was the first study to compare the three types of tea and BMD in both sexes concomitantly. Duration of tea consumption, not amount of daily tea consumption, was the only independent determinant of BMD. The authors found that the change of BMD is always gradual. Long-term, moderate tea consumption appears to influence BMD more than short-term consumption of high amounts of tea.
According to the authors, tea's bone protective effects may be due to its fluoride content. Fluoride intake can alleviate osteoporosis progression. Also, tea contains flavonoids which have been shown to improve BMD. (The authors mistakenly suggest tea contains ipriflavone - a synthetic flavonoid preparation not found in tea.) Any or all of these hypotheses may explain tea's protective effect on BMD.
-Heather S. Oliff, Ph.D
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