Green Tea and the Kidneys

How does green tea affect the kidneys? Recent animal studies have highlighted some interesting results. As many people know, one of the most important functions of the kidneys is to remove wastes from the bloodstream. These wastes include excess water and nutrients, as well as the byproducts of cellular processes and substances taken up by the body through the digestive system, skin, and lungs. However, there are some circumstances when kidney functioning may be impaired. A few of these circumstances include kidney disease that results from having diabetes (diabetic nephropathy), kidney stones, low blood supply to the organs (ischemia), and blood coagulation or clotting (thrombosis). A plethora of new animal studies now show that green tea may have the potential to improve these conditions. It might also help maintain the function of our kidneys in spite of these serious health problems.

Diabetes mellitus is a serious condition that affects an increasing number of people. This condition can lead to kidney disease, or nephropathy [1]. When diabetes mellitus progresses to kidney disease, there is damage to the kidneys and their ability to function. Research published in the British Journal of Nutrition investigated rats with diabetic nephropathy that were fed a concentration of 16% green tea as their only drinking source for 12 weeks. These animals experienced a number of benefits.

They showed lower levels of nitrogen in their blood, as well as the waste products creatinine and malondialdehyde [2]. These waste products must be filtered out of the bloodstream by the kidneys. In addition, less glucose and protein were found in the rats’ urine, showing that there was an improvement in their kidney function [2]. This research clearly shows that green tea helps the kidney function in rats with diabetes and raises interesting questions for humans.

Kidney stones are painful and disrupt the functioning of the kidney. Oxalate is a compound that promotes the growth of kidney stones (also called “calcium oxalate stones”). It also kills the tubular epithelial cells, which line the inside of the kidneys. As a result of damage to these cells, crystals of calcium oxalate stick more easily to them, making it more likely that a kidney stone will develop [4]. A study published in the Journal of Endourology looked at the cells lining rat kidneys and the effects of

EGCG (a compound in green tea). Rats given EGCG experienced remarkable benefits from it. The compound prevented free radical production by oxalate and also cut down on the number of crystals formed in their kidneys. Since EGCG is the main component in green tea, green tea is involved in preventing kidney stone formation. Researchers from the Institute of Biophysics noted that green tea itself contains many polyphenols with antioxidant properties, which means it can help control the damage caused by free radicals [5].

Renal ischemia is a serious condition where the kidneys do not get enough oxygen for a certain period of time. A lack of oxygen leads to inflammation and damage in the kidneys once blood and oxygen are reintroduced; this is referred to as a reperfusion injury. Renal Ischemia/ Reperfusion (I/R) cause many problems in the kidneys. Some of these problems include a lower glomerular filtration rate, which refers to how much blood is being moved through the tiny filters in your kidneys. The blood flow through the kidneys is important because it takes out the waste product creatinine. Another serious problem that comes from not getting enough oxygen is damage and the eventual death of tissue in the kidneys [6].

A 2006 study published in Transplantation Proceedings examined rats with renal I/R. The researchers found that three indicators of kidney function blood urea nitrogen levels (BUN), serum creatinine (sCr), and creatinine clearance (CrCl) levels improved in rats that were given EGCG (10 mg/kg) after renal I/R injury [6]. In addition, the rats given EGCG also had lower tissue death in their kidneys, as well as increased regeneration of these tissues after the damage. This research highlights the beneficial effects of EGCG: it limited damage to the kidneys, promoted tissue regeneration, and maintained the function of the kidneys [6].

Scientists at the Nestlé Research Center in Switzerland examined diabetic rats and the formation of blood clots (thrombosis) [7]. Blood clots impair kidney function by causing the kidney tissue to die. Research published in the Asia Pacific Journal of Clinical Nutrition showed that green tea given to rats helped to restore the proper balance of chemicals that prevents the formation of blood clots [8].

This study highlights the antithrombotic effect of green tea in rats with diabetes. Isn’t it possible that green tea may also benefit other vascular conditions such as hypertension and atherosclerosis? 

These animal studies highlight some interesting effects green tea has on bodily systems. All of these studies examined serious issues related to diabetes (like tissue death, kidney stones, low oxygen levels, and blood clots). What may be the benefits of green tea in regards to healthy kidneys? As research into the influence that green tea has on the kidneys continues, our understanding of the role that green tea plays on the day-to-day functioning of the kidneys will only improve.

References

1. Selby Jv, F.-S.S.C.N.J.M.K.P.P.S.S.S.J., The natural history and epidemiology of diabetic nephropathy: Implications for prevention and control. JAMA, 1990. 263(14): p. 1954-1960.

2. Renno, W.M., et al., Effect of green tea on kidney tubules of diabetic rats. British Journal of Nutrition, 2008. 100(03): p. 652-659 M3 – 10.1017/S0007114508911533.

3. Hackett, R.L., P.N. Shevock, and S.R. Khan, Madin-Darby canine kidney cells are injured by exposure to oxalate and to calcium oxalate crystals. Urological Research, 1994. 22(4): p. 197-203.

4. Byong Chang Jeong, B.S.K., Jung In Kim, and Hyeon Hoe Kim, Effects of Green Tea on Urinary Stone Formation: An in Vivo and in Vitro Study. Journal of Endourology, 2006. 20(5): p. 356-361.

5. Guo, Q., et al., Studies on protective mechanisms of four components of green tea polyphenols against lipid peroxidation in synaptosomes. Biochimica et Biophysica Acta (BBA) – Lipids and Lipid Metabolism, 1996. 1304(3): p. 210-222.

6. Jang, Y.H., et al., Polyphenol (-)-Epigallocatechin Gallate Protection from Ischemia/Reperfusion-Induced Renal Injury in Normotensive and Hypertensive Rats. Transplantation proceedings, 2006. 38(7): p. 2190-2194.

7. Crespy, V. and G. Williamson, A Review of the Health Effects of Green Tea Catechins in In Vivo Animal Models. The Journal of Nutrition, 2004. 134(12): p. 3431S-3440S.

8. Rhee, S.-J., M.-J. Kim, and O.-G. Kwag, Effects of green tea catechin on prostaglandin synthesis of renal glomerular and renal dysfunction in streptozoto- cin-induced diabetic rats. Asia Pacific Journal of Clinical Nutrition, 2002. 11(3): p. 232-236.