Diabetes mellitus remains one of the most common diseases. One of its signs, hyperglycemia, is a major predisposing factor for oxidative stress, as it disrupts the natural equilibrium that protects the body from tissue-damaging effects of free radicals. In patients with diabetes mellitus, oxidative stress can lead to microvascular and macrovascular complications precipitated by the disequilibrium between antioxidant enzymes and free radicals. In traditional Iranian medicine, stinging nettle (common nettle; Urtica dioica, Urticaceae) is used for its hypoglycemic and anti-inflammatory properties. This randomized, double-blind, clinical trial evaluated the effects of a hydro-alcoholic extract of stinging nettle on blood lipids, hepatic enzymes, and nitric oxide levels in patients with type 2 diabetes mellitus.
Recruited from February 2014 to May 2014, 50 women with type 2 diabetes who attended the Diabetes Society of Shahroud affiliated with Shahroud University of Medical Sciences in Shahroud, Iran, were included in the study. The women were older than 50 years, had glycated hemoglobin (HbA1c) levels ≤10% and triglyceride levels <400 mg/dL, and were using the diabetes medications metformin or glibenclamide. Those who had cardiovascular, liver or kidney disease, allergies, or who regularly used nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, alcohol, or insulin injections were excluded.
The women were randomly assigned into 2 groups of 25 each and were to receive either 5 mL hydro-alcoholic extract of stinging nettle or a placebo of water, alcohol, and chlorophyll color 3 times daily after each meal for 8 weeks. Both treatments were placed as liquids in bottles of identical appearance. The hydro-alcoholic extract of stinging nettle and placebo were prepared by Giah Essence Company (Gorgan, Golestan, Iran). The patients were instructed to consume each portion dissolved in 1 glass of water and to complete a 24-hour dietary recall for 3 days (2 weekdays and 1 weekend day) at baseline and at the end of the study. The study investigators contacted each patient weekly for any reports of adverse effects, including nausea and reflux, along with the signs and symptoms of interactions with pharmacological medications.
Of the 25 patients in the nettle group, 1 withdrew voluntarily; in the placebo group, 2 discontinued the study because of a lack of efficacy. A total of 47 patients completed the study, with 24 patients in the nettle group and 23 patients in the placebo group. [Note: This is according to the study flowchart in Figure 1. There are discrepancies among the article text, Table 1, and Figure 1. The article text states that 48 patients completed the study, with 24 patients in each group; Table 1 has n=23 for the nettle group and n=24 for the placebo group.]
No significant between-group differences were seen at baseline in demographic and biochemical characteristics. At the end of 8 weeks of treatment, significant decreases were seen in fasting plasma glucose (P<0.01) and triglyceride levels (P<0.05) in the nettle group compared with the placebo group. High-density lipoprotein cholesterol levels increased significantly in the nettle group compared with the placebo group (P<0.05), which recorded decreased levels. No significant between-group differences were seen in changes in low-density lipoprotein cholesterol levels. The effects on fasting blood sugar were thought to be due to stinging nettle’s inhibitory effects on alpha-glucosidase, resulting in lower blood sugar.
The determination of hepatic enzyme levels revealed significantly lower levels of serum glutamic pyruvic transaminase in the nettle group compared with the placebo group at the end of 8 weeks (P<0.05 in Figure 3; P<0.001 in the article text), but no significant between-group differences in changes in serum glutamic oxaloacetic transaminase levels. Increases in antioxidant levels were significantly greater in the nettle group compared with the placebo group after 8 weeks (for nitric oxide, P<0.01 in Figure 4 [P<0.001 in the article text]; for superoxide dismutase, P<0.05 in Figure 4 [P<0.001 in the article text]). In the placebo group, superoxide dismutase levels decreased during the trial.
This study was limited by its small sample size, lack of complete control of diet and exercise of the patients, and the short duration, which may have ruled out additional beneficial effects or adverse effects seen later with the nettle treatment.
In earlier studies, stinging nettle has been shown to cause antidiabetic and blood glucose-reducing effects and exert antihyperlipidemic and antihyperglycemic activities in type 2 diabetic rats. Another study concluded that common nettle protects against oxidative stress in hyperglycemic rats.
“Our results showed that hydro-alcoholic extract of U. dioica is an interesting source of bioactive compounds and may decrease the diabetes-related risk factors of cardiovascular incidence and other complications in patients with diabetes mellitus,” the authors conclude.
Amiri Behzadi A, Kalalian-Moghaddam H, Ahmadi AH. Effects of Urtica dioica supplementation on blood lipids, hepatic enzymes and nitric oxide levels in type 2 diabetic patients: a double-blind, randomized clinical trial. Avicenna J Phytomed. 2016;6(6):686-695.