Nowadays, diabetes mellitus (DM) is the most common widespread chronic metabolic disease. The number of people suffering from it is steadily increasing. During 2010, the number of adults with diabetes came to 285 million. They estimate that by the year 2030, this number would reach up to 439 million. In Iran, 2 million adults were reported to have diabetes during 2005.
Clinical trials have shown that oxidative stress plays an important role in causing the adverse effects of both types of diabetes. An increase in free oxidized radicals will lead to an increase in peroxidation of lipids and insulin resistance. Patients with insulin resistance are at risk of developing metabolic syndrome. This syndrome is the main cause of heart disease, dyslipidemia and hypertension. By decreasing oxidative stress and following that, decreasing insulin resistance, the incidence and severity of the adverse effects of diabetes might also decrease.
Due to DM-related morbidity/mortality and also positive effects of several kinds of tea (particularly hibiscus tea and green tea), investigating the effects of these teas on DM seems to be vital.
Hibiscus tea/Sour tea (Hibiscus Sabdariffa) contains flavonoids. Its dry calyces contain the flavonoids gossypetine, hibiscetine, and sabdaretine, alkaloids, β-sitosterol, anthocyanin, citric acid, cyanidin-3-rutinose, delphinidin, galactose, pectin, protocatechuic acid, quercetin, stearic acid, wax, a small amount of delphinidin-3-monoglucoside, and cyanidin-3-monoglucoside. Moreover, the calyces contain crude protein and minerals (such as iron, phosphorus, calcium, manganese, aluminum, magnesium, sodium, potassium), Mucilage, calcium citrate, ascorbic acid, gossypetin, hibiscin chloride, and are also rich in acid and pectin. (2)
Each of these composites can have various effects on the human body. Different clinical trials were done to show the effects of hibiscus tea on humans and animals. They have shown hibiscus tea's several positive effects like systolic and diastolic blood pressure decrease.
Its phenolic protocatechuic acid has protective antioxidant effects on the liver and causes apoptosis (a form of programmed cell death) of cancer cells. Anthocyanins present in hibiscus tea like delphinidin 3-sambubioside also have the same effect.
Green tea (Camellia Sinesis) is enriched with flavonoids, polyphenols, catechin, epicatechin, epigallocatechin, epigallocatechin-3-gallate, and also contains other composites like caffeine, tannins, vitamins, and saponins. People around the world use it as herbal medicine.
Several studies indicate that catechin and gallic acid present in green tea lead to antioxidant, antimutagenic, antibacterial, anti-inflammatory, and hypocholesterolemia activity.
Some investigations also reveal that catechin found in green tea inhibits the proliferation of breast cancer cells in vitro studies.
As mentioned, green and hibiscus tea both contains flavonoids and various polyphenols which have the anti-oxidative and anti-inflammatory function.
In 2011-2012, a randomized clinical trial was carried out to compare the effect of sour and green tea on insulin resistance and oxidative stress in DM. The participants were 100 patients with type 2 diabetes mellitus.
Inclusion criteria were:
(1) Age: 30 to 60 years old
(2) DM duration: at least 5 years
(3) Fasting blood sugar: 80-250mg/dl
(4) No obvious DM complications, like nephropathy, etc.
(5) Non-insulin dependent
(6) Non-smoker or addiction to certain illicit drugs
(7) No history of using dietary supplements like antioxidants, multivitamins with minerals, and omega-3 during the last 6 months
(8) No history of organ diseases like renal, thyroid, liver, or heart disease.
Exclusion criteria were:
(1) A change in the participants’ main usual diet
(2) Allergy to hibiscus tea or green tea
(3) A change in the dose or drug used as glucose-lowering agents and anti-lipid agents
(4) Reluctant participation
The patients were randomly divided into two groups of hibiscus tea and green tea. They were advised to prepare their teas according to the instructions and drink teas three times a day (2 hours after the main meal) for four weeks.
- The green tea group was instructed to add one teabag, containing 3 grams of green tea, in 150ml of hot water (at 60-70oC) and drink it after 5 minutes.
- The hibiscus tea group was instructed to add one teabag, containing 3 grams of hibiscus tea, in 150ml of hot water (at 60-70oC) and drink it after 10-15 minutes.
* If not interested in tea flavor, they were allowed to consume one date palm.
Then, the researchers monitored fasting blood sugar (FBS), fructosamine, lipid profiles (triglyceride, total cholesterol, HDL-c, and LDL-c), fasting blood insulin (FBI), and malondialdehyde. They also assessed insulin resistance status using the following indices: Homeostasis model assessment of insulin resistance (HOMA-IR), level of β-cell function (b %), and insulin sensitivity (S %).
The results indicate that drinking hibiscus tea and green tea three times a day for 4 weeks has different effects on insulin resistance and certain lipoprotein in patients with type 2 diabetes mellitus.
HDL-c increased significantly in both groups. It appears that both kinds of tea are beneficial for patients with type 2 diabetes, but green tea has a better effect on insulin resistance indices than hibiscus tea.
They observed less insulin sensitivity, and therefore, more insulin resistance in the hibiscus tea group. Similar to the previous studies, this study also indicates that hibiscus tea not only has no effect on FBS but also does not have any significant positive effect on lipoprotein profile except on HDL-c. On the other hand, one clinical trial shows that hibiscus tea has positive effects on HDL-c and decreases other lipoproteins. Some studies conclude that the effect of hibiscus tea on lipoprotein is due to water-soluble fibers identified in this tea.
Similar to the previous studies, this study also shows that green tea has no effect on FBS. However, there are few studies demonstrating that green tea has an effect on FBS. Although few investigators claim that green tea has no effect on lipid profile, the present study indicates that it increases HDL-c. In this clinical trial, as well as others, they observed that fasting blood insulin significantly decreased in green tea users. It should be noted that few other clinical trials did not show any changes in fasting blood insulin.
This discrepancy might be caused by the intervention duration and the method of tea brewing:
The intervention period in the present study was 4 weeks compared with 8 to 12 weeks in other clinical trials. In past studies, they used green tea capsules, but in the current study, the infusion was prepared in hot water.
At the end of the intervention, mean insulin sensitivity decreased significantly in hibiscus tea users but was less compared with the green tea users.
They observed no difference in mean MDA in both groups before and after the intervention. Although in the past human model studies, the effect of hibiscus tea on MDA has not been reported too, two animal model studies show that hibiscus tea decreases MDA. Similar to other studies, it shows that green tea has no effect on mean MDA. However, in a study on healthy humans, Freese et al. conclude that green tea decreases MDA. These teas contain different kinds of antioxidants and therefore, this conclusion is debatable to various investigators.
According to the study results, when patients with type 2 diabetes consumed hibiscus tea or green tea, their HDL-c was significantly increased. Hibiscus tea also increased β-cell function of the pancreas and therefore, increased fasting blood insulin.
With respect to the current study and other investigations, both green tea and hibiscus tea have positive effects in patients with dyslipidemia, particularly in patients with diabetes. This study shows that consuming 150 ml green tea or hibiscus tea infusion, three times a day for four weeks, has positive effects on insulin resistance and certain lipoproteins in type 2 DM. Accordingly, green and hibiscus tea consumption is recommended. (1)
1. Mozaffari-Khosravi, H., Ahadi, Z., & Tafti, M.F. (2014). The Effect of Green Tea versus sour tea on Insulin Resistance, Lipids Profiles and Oxidative Stress in Patients with Type 2 Diabetes Mellitus: A Randomized Clinical Trial. Iranian Journal of Medical Sciences, 39(5), 424–432. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4164889/
2. Mahadevan, N., & Shivali, P.K. (2009). Hibiscus sabdariffa Linn.-An overview. Natural Product Radiance, 8(1), 77–83. Retrieved from http://nopr.niscair.res.in/bitstream/123456789/3769/1/NPR%208(1)%2077-83.pdf