It has been more than a decade since I last focused on the health benefits of green tea, an everyday food with a remarkable story. In past articles I have written about research revealing the role of green tea (Camellia sinensis) in preventing cancer and heart disease. In addition, results from the large Ohsaki study in Japan, showed that drinking green tea reduced the likelihood of death from any cause, but especially from strokes.
The amount of clinical and epidemiological evidence for green tea is now huge and growing at a fast rate, so an update on some of the key studies is overdue.
Green tea helps with heart disease
Amyloidosis is a mysterious, rare and potentially life-threatening progressive disease where amyloid proteins are deposited in organs and tissues. Symptoms vary with the organs affected, often including the heart, kidneys, nervous system and digestive tract. There’s no known cure and most conventional treatments are experimental and at best palliative.
A case report was published of a 76-year-old man (in fact an emeritus medical professor) who was diagnosed with systemic light-chain amyloidosis after presenting with dizziness and progressive fatigue.1 The patient’s tongue, heart and kidneys were affected and after initial drug treatment to stabilise his condition, no further medications were prescribed. When the retired professor heard about research on a component of green tea that prevented the generation of amyloid in the lab, he began to consume 1.5 to 2 litres a day of green tea.
After 11 months his quality of life had improved, his bleeding tendency had normalised, he had stable (but still impaired) renal function and his cardiac function was enhanced. The enlargement in the septum (middle dividing part) of his heart also decreased substantially.
This report was followed up by an observational study of 11 patients. The patients were selected because they were already drinking 1.5 to 2 litres a day of green tea or, in two cases, a green tea extract (containing 600-800mg/day EGCG).2 The 11 patients using green tea were compared to a matched historic control group of 22 patients. All study participants were receiving conventional medical treatment if appropriate. After a follow-up period of about six months, many cardiac measures were significantly improved in the green tea group (compared to the initial observation and, in some instances, the control group), where the control group demonstrated no improvement or even deterioration. The most important changes were for the ventricular parameters. Ventricular wall thickness (interventricular septum) and left ventricular mass fell significantly with green tea compared to the control group. Heart function was also substantially improved. All these findings indicate a reduction in cardiac congestion, which was also reflected in their improved heart symptoms.
The authors noted that conventional treatment has been able to reduce left ventricular wall thickness in only one earlier trial, and then in just 15% of the patients under study. In contrast, all the patients taking green tea showed a wall thickness reduction of at least 2mm. Furthermore, the four patients in the green tea group who came to the next routine follow-up examination had further reductions, with an average reduction of 5mm.
The implications of this study go well beyond the immediate clinical application, as promising as they are. The detractors of herbal therapies often pursue three lines of argument: that herbs are too gentle to exert profound effects in serious diseases, that if commonly known and used herbs (like green tea) had important clinical activities we would have already discovered them by now (and made a drug from the herb, like in the case of morphine) and that users of herbs who have medical conditions risk dangerous interactions with their conventional medications. This study suggests that in all three instances the opposite can be true.
Fight back against fibroids
Recently published trials and systematic reviews point to the clinical versatility of green tea. Of particular interest is the double-blind, randomised, controlled trial in women with symptomatic uterine fibroids (UF).3 Researchers recruited 39 reproductive-age women with fibroids for the study. All had at least one fibroid lesion 2cm3 or larger, as confirmed by transvaginal ultrasonography. They were randomised to oral daily treatment with either 800mg of green tea extract (45% EGCG) or a placebo (800mg of brown rice) for four months, and fibroid volumes were measured at the end. The fibroid-specific symptom severity and health-related quality of life (HRQL) of these patients were scored at each monthly visit. Of the final 39 women recruited for the study, 33 completed all five visits of the study. In the placebo group (n=11), fibroid volume increased (24.3%) over the study period. However, patients taking green tea extract (n=22), showed a significant reduction in total volume by 36%.
In addition, green tea treatment significantly reduced fibroid-specific symptom severity by 32.4%, and induced a significant improvement in HRQL, compared to the placebo group. Anaemia also significantly improved in the treatment group, while average blood loss significantly decreased from 71mL/month to 45mL/month. No adverse effects, endometrial hyperplasia and other endometrial pathology were observed in either group.
Min Zhang (in collaboration), currently based at the University of Western Australia, combined the results of six investigations conducted in China over the past decade with co-workers into the role of green tea in cancer prevention.4 One epidemiological investigation was a prospective cohort study (n=254) and the other five were observational case-control studies. Higher green tea consumption was consistently observed as being associated with a lower risk of mortality due to ovarian cancer, and a decreased risk of ovarian, breast, and colorectal cancers, and adult leukaemia occurrences in the observational studies. The adjusted hazards ratio (HR) and 95% confidence interval (CI) for mortality from ovarian cancer was 0.40 (0.18 to 0.90) in the patients who consumed green tea at the highest level, compared with non-tea drinkers. Compared with never or seldom tea drinkers, the adjusted odds ratio (OR) ranged from 0.07 to 0.61 for ovarian, breast, and colorectal cancers and adult leukaemia in those who consumed green tea at the highest level.
Overall though, population studies on the association between green tea consumption and breast cancer risk have yielded mixed results. A 2013 update of the evidence from all available studies found no significant association between green tea consumption and reduced breast cancer risk.5 A review published in 2012 found some positive evidence for breast cancer risk reduction with green tea consumption, but stressed that current evidence was inconclusive.6
Population-based studies of cancer risk are a blunt instrument, perhaps explaining why a recent study took a different perspective, examining the association between green tea intake and oestrogen profile. A group of US scientists from the National Cancer Institute examined the association between green tea use and urinary oestrogen profiles in Japanese-American women.7 Their findings received considerable publicity.
Researchers divided the 191 women (119 premenopausal in luteal phase and 72 postmenopausal) into three groups based on their green tea intake (<1 time/week, one to six times weekly, or seven or more times weekly). In the premenopausal women, intake of green tea was associated with lower luteal total phase oestrogen metabolites and lower urinary (16-hydroxylated oestrogen) pathway metabolites. In postmenopausal women, urinary oestrone and oestradiol were about 20% and 40% lower, respectively, in women drinking green tea daily compared to those drinking it less than once a week. Levels of caffeine intake did not change these associations, and there was no influence from black tea consumption.
The authors noted that while other studies have shown some differences in urinary oestrogen metabolites with green tea drinking, this was the first to analyse the association for a broad range of oestrogen metabolites in peri- and postmenopausal women. They also suggested that because aromatisation of androgens accounts for postmenopausal oestrogens, lower oestrogens in association with green tea use suggests possible inhibition of the enzyme aromatising. (Some current drugs used to treat oestrogen-sensitive breast cancers are aromatase inhibitors.) All of this of course speaks to possible reduction in breast cancer risk with green tea, due to a lower exposure to oestrogen, including its more active metabolites.
Better blood sugar with green tea
Type 2 diabetes is a huge challenge for modern communities. Hence, any natural treatments with a high‑level evidence of working are of immense relevance. Clinical trials of green tea products have yielded inconsistent results here. Consequently, a team of Chinese scientists undertook a meta-analysis of trials investigating the impact of green tea (as extract or beverage) on glucose control and insulin sensitivity. With meta-analysis, the results of several smaller trials are combined into one big trial. The meta-analysis included a variety of participants, including those with type 2 diabetes and insulin resistance, or of normal health.8 Seventeen relevant trials in more than 1,000 people were located and included. Green tea consumption significantly reduced fasting glucose and haemoglobin A1c (HbA1c) concentrations. Further analysis from high quality studies found green tea also significantly reduced fasting insulin. No significant publication bias (omission from publication of negative studies) was detected. Subgroup analyses revealed that green tea lowered fasting blood glucose in those at risk of metabolic syndrome, but had no such effect in healthy participants.
To your better health,
Nutrition & Healing
Vol. 8, Issue 11 – November 2014
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