Groene thee tegen kanker en voor goede bloedsuikerwaarden*
Uit twee studies blijken de grote voordelen van het regelmatig drinken van groene
thee. Uit een Chinese studie onder ruim 69.000 vrouwen die 11 jaar gevolgd werden blijkt dat zij die meer dan drie keer per week groene thee drinken een duidelijk kleinere kans hebben op het krijgen van maag-, slokdarm- en darmkanker. Hoe langer en hoe meer groene thee gedronken wordt hoe kleiner die kans
was. Uit een andere studie, weliswaar met muizen blijkt dat het drinken van groene thee tijdens het eten een duidelijk lagere piek in de
bloedsuikerspiegel laat zien. In de studie kregen de muizen voer met
zetmeel, vergelijkbaar met een ontbijt met brood en broodjes. Normaal geeft dat na het eten hiervan een duidelijk piek in de bloedsuikerwaarden. De muizen die het eten aangevuld kregen met groene thee extracten bleken een 50% lagere piek te krijgen dan de muizen die de aanvulling niet kregen. Groene thee extracten bevatten veel
catechinen, vooral EGCG en de hoeveelheid die de muizen kregen is vergelijkbaar met anderhalve kop groene thee voor mensen.
De catechinen bleken in de studie de snelheid van afbreken van het zetmeel in
maltose en glucose danig te vertragen.
Prospective cohort study of tea consumption and risk of digestive system
cancers: results from the Shanghai Women's Health Study1,2,3
1. Sarah Nechuta, 2. Xiao-Ou Shu, 3. Hong-Lan Li, 4. Gong Yang, 5. Bu-Tian
Ji, 6. Yong-Bing Xiang, 7. Hui Cai, 8. Wong-Ho Chow, 9. Yu-Tang Gao, and 10. Wei Zheng
+ Author Affiliations
1. 1From the Division of Epidemiology, Department of Medicine, Vanderbilt University School of
Medicine, Nashville, TN (SN, X-OS, GY, HC, and WZ); the Department of
Epidemiology, Shanghai Cancer Institute, Shanghai, China (H-LL, Y-BX, and Y-TG); and the Division of Cancer Epidemiology and
Genetics, National Cancer Institute, Rockville, MD (B-TJ and W-HC).
+ Author Notes
· ↵2 Supported by the National Cancer Institute (grant number R37 CA70867).
· ↵3 Address correspondence to W Zheng, Vanderbilt Epidemiology Center and Vanderbilt-Ingram Cancer Center, Vanderbilt University School of
Medicine, Eighth Floor, Suite 800, 2525 West End Avenue, Nashville, TN 37203-1738. E-mail:
wei.zheng@vanderbilt.edu.
Abstract
Background: Data from in vitro and animal studies support a protective role for tea in the etiology of digestive system
cancers; however, results from prospective cohort studies have been inconsistent. In
addition, to our knowledge, no study has investigated the association of tea consumption with the incidence of all digestive system cancers in Chinese
women.
Objective: We investigated the association of regular tea intake (≥3 times/wk for >6
mo) with risk of digestive system cancers.
Design: We used the Shanghai Women's Health Study, a population-based prospective cohort study of middle-aged and older Chinese women who were recruited in 1996–2000. Adjusted HRs and associated 95% CIs were derived from Cox regression models.
Results: After a mean follow-up of 11 y, 1255 digestive system cancers occurred
(stomach, esophagus, colorectal, liver, pancreas, and gallbladder/bile duct
cancers) in 69,310 nonsmoking and non–alcohol-drinking women. In comparison with women who never drank
tea, regular tea intake (mostly green tea) was associated with reduced risk of all digestive system cancers combined
(HR: 0.86; 95% CI: 0.74, 0.98), and the reduction in risk increased as the amount and years of tea consumption increased
(P-trend = 0.01 and P-trend < 0.01, respectively). For example, women who consumed ≥150 g
tea/mo (∼2–3 cups/d) had a 21% reduced risk of digestive system cancers combined
(HR: 0.79; 95% CI: 0.63, 0.99). The inverse association was found primarily for colorectal and
stomach/esophageal cancers.
Conclusion: In this large prospective cohort study, tea consumption was associated with reduced risk of colorectal and
stomach/esophageal cancers in Chinese women
Drinking green tea with starchy food may help lower blood sugar spikes
UNIVERSITY PARK, Pa. -- An ingredient in green tea that helps reduce blood sugar spikes in mice may lead to new diet strategies for people, according to Penn State food scientists.
Mice fed an antioxidant found in green tea -- epigallocatechin-3-gallate, or EGCG -- and corn starch had a significant reduction in increase in their blood sugar -- blood glucose -- levels compared to mice that were not fed the compound, according to Joshua Lambert, assistant professor of food science in agricultural sciences.
"The spike in blood glucose level is about 50 percent lower than the increase in the blood glucose level of mice that were not fed EGCG," Lambert said.
The dose of EGCG fed to the mice was equivalent to about one and a half cups of green tea for a human.
Lambert, who worked with Sarah C. Forester, postdoctoral fellow, and Yeyi Gu, graduate student, both in food science, said EGCG was most effective when the compound was fed to the mice simultaneously with corn starch. For humans, this may mean that green tea could help them control the typical blood sugar increases that are brought on when they eat starchy foods, like breads and bagels that are often a part of typical breakfasts.
"If what you are eating with your tea has starch in it then you might see that beneficial effect," Lambert said. "So, for example, if you have green tea with your bagel for breakfast, it may reduce the spike in blood glucose levels that you would normally get from that food."
The EGCG had no significant effect on blood sugar spikes in mice that were fed glucose or maltose, according to the researchers who released their findings in the online version of Molecular Nutrition and Food Research. Lambert said that the reason blood sugar spikes are reduced when the mice ate starch, but not these sugars, may be related to the way the body converts starch into sugar.
An enzyme called alpha-amylase that is produced in both the mouth and by the pancreas helps break down starch into maltose and glucose. EGCG may inhibit the enzymes ability to break down the starch, the researchers indicated, since they also found that EGCG reduced the activity of alpha amylase in the pancreas by 34 percent.
If the mechanism holds in humans, this may mean that people who want to limit the blood sugar spike should skip adding sugar to their cup of green tea.
"That may mean that if you add sugar into your green tea, that might negate the effect that the green tea will have on limiting the rise in blood glucose level," Lambert said.
Lambert added that the green tea and the starch would need to be consumed simultaneously. For example, drinking a cup of tea well after eating a piece of toast would probably not change the blood sugar spike.
For the study, researchers separated mice into several groups based on body weight. After a fasting period, the mice were given common corn starch, maltose, or sucrose. One group of mice received EGCG along with the feed, while a control group was not fed the compound.
The researchers then tested the blood sugar levels of both groups.
Lambert said the researchers next step is to test the compound on people.
"The relatively low effective dose of EGCG makes a compelling case for studies in human subjects," the researchers
said.
(November 2012)
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