And drinking more cups appears to confer additional risk reductions, with five or more cups a day associated with a 23 per cent reduction in risk, according to findings from the Ohsaki Cohort 2006 Study published in Preventive Medicine.
Being an observational study, the findings do not prove causality, but the link does appear to be biologically plausible, state the authors, led by Yasushi Koyama from Tohoku University Graduate School of Medicine. Previous studies have reported that green tea catechins may inhibit the action of oral bacteria linked to development of periodontal disease, they said.
“A number of experimental studies have shown that green tea catechins inhibit oral bacteria, while some experiments have indicated that the concentration of tea catechin conferring the above effect should be more than 100 mg/100 ml,” wrote the authors. “A typical preparation of green tea contains a catechin concentration of 50–150 mg/100 ml.
“Therefore, this amount of catechin contained in one cup of green tea might be sufficient to aid tooth retention,” they added.
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, as well as aiding in weight management.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
The success has translated into a booming extract market, valued at a around $44m (€29.7m), according to recent report from Frost & Sullivan. The market is expected to grow by more than 13 per cent over the next seven years. Key players include DSM, Taiyo, and Tate & Lyle. Innovation in delivery has also seen companies like Maxx Performance release an encapsulated green tea extract for bakery applications.
Koyama and co-workers analysed data from 25,078 people aged between 40 to 64 years. By measuring tooth loss in people with up to 20 teeth still remaining, the researchers calculated that one to two cups of green tea per day was associated with an 18 per cent reduction in tooth loss risk. The same reduction was calculted for three to four cups per day, while five or more cups was associated with a 23 per cent reduction in risk. If the researchers limited or extended the data for people with less than ten, or up to 25 teeth, the same protective levels of green tea consumption were obsered.
The researchers noted that the a certain level of tea was required to produce the effect. This ‘threshold’ value could be linked to the catechin content of green tea, they added.
Source: Preventive Medicine
Published online ahead of print, doi: 10.1016/j.ypmed.2010.01.010
“Association between green tea consumption and tooth loss: Cross-sectional results from the Ohsaki Cohort 2006 Study”
Authors: Y. Koyama, S. Kuriyama, J. Aida, T. Sone, N. Nakaya, K. Ohmori-Matsuda, A. Hozawa, I. Tsuji