Clinical Trial Finds that Walnut Leaf Extract is Ineffective for Reducing Cardiovascular Risk Factors Associated with Type 2 Diabetes
Walnut (Juglans regia, Juglandaceae) is a large deciduous tree native to Central Asia. It has been in cultivation across the Eurasian continent for thousands of years. While it is primarily grown for its exceptionally nutritious nut, it is also a source of dye, wood, and other products. In this double-blind, placebo-controlled, parallel group, clinical trial, the researchers evaluated the effects of a walnut leaf extract on glycemic control and cardiovascular risk factors in patients with type 2 diabetes.
Walnut leaves for this study were collected in the Dasht-e Naz agricultural area outside the city of Sari, Iran. They were positively identified and certified by a botanist, and a botanical quality voucher specimen was deposited at the Sari School of Pharmacy. The walnut leaf sample was air-dried at room temperature. One kilogram of the sample was ground and percolated, using three 2.5 L measures of 70% ethanol over 24 hours. The resulting extract was concentrated in a rotary evaporator to obtain a crude extract, which was then freeze-dried, ground to a powder, mixed with microcrystalline cellulose (Avicel) at a 1:4 ratio, and encapsulated. Each capsule of the extract contained 100 mg extract and 400 mg Avicel. The placebo capsules contained 500 mg Avicel. The extract was standardized to 40±1.3 mg gallic acid per gram of extract and manufactured in accordance with United States Pharmacopeia methods.
Patients in the study were recruited from the diabetes outpatient academic clinic at the Imam Khomeini Hospital in Sari, Iran in 2012 and 2013. Included patients were aged 30 to 80 years, had glycosylated hemoglobin (HbA1c) of over 7%, and were receiving maximal doses of the anti-diabetic agents’ metformin and glibenclamide. There were many exclusion factors, including other diseases, recent extreme weight loss, current use of a corticosteroid or thiazide diuretic, high serum creatine level, pregnancy or lactation, changes in anti-diabetic drug type, and lack of follow-up.
The 50 selected patients were randomly allocated to treatment and control groups. There were no statistically significant differences between the two groups at the beginning of the study. The patients were instructed not to change their diet or drugs during the course of the eight-week study. Patients received one capsule per day for the first week of the study period and two capsules per day for the following seven weeks. The following data were collected at baseline and at the end of the study: body weight, body mass index (BMI), blood pressure (BP), fasting blood sugar (FBS), serum insulin, HbA1c, postprandial blood glucose (PPG), serum lipid profile, and liver function panel. Insulin resistance was estimated using the homeostasis model assessment-estimated insulin resistance method (HOMA-IR), which is calculated from the levels of fasting plasma insulin and fasting plasma glucose.
For the statistical analysis of quantitative variables, Student’s t-test and paired t-test were used to compare the two groups to each other and for before-after values within the groups. For qualitative analysis, Chi-square and Fisher exact tests were used to compare the two groups. The researchers considered P<0.05 to be statistically significant.
Each group started with 25 patients. Twenty patients in the treatment group and 19 in the control group completed the study. All lost patients were excluded because they changed diabetes drug type during the study. The mean age of patients in both groups was about 50 years, most had a history of hypertension and dyslipidemia, and almost all were female.
No statistically significant effect was found in either group for the following measures: FBS, PPG, HbA1c, insulin resistance, and lipid profile. Using the standards set by the researchers, the following measures showed statistical significance in the walnut leaf group compared to baseline: reduced body weight (P=0.028), reduced BMI (P=0.030), and reduced systolic BP (P=0.005). They also found the following statistically significant changes in the control group compared to baseline: reduced PPG (P=0.030), reduced HbA1c (P=0.028), and reduced serum alanine transaminase level (P=0.044). There were no statistically significant differences between the two groups for any outcome at the end of the intervention.
The researchers note an important accidental finding in this study. Avicel, commonly used in pharmacy as a filler, flow agent, and spheronization agent for encapsulation and in medical research as a placebo, may itself have significant effects on blood sugar and liver enzyme levels. It may be an inappropriate placebo for studies on blood sugar or potentially a stand-alone treatment for diabetic symptoms. It is a fine powder of acid-hydrolyzed cellulose obtained from wood and other plant fibers. The name is trademarked by the FMC Corporation, and the product for this study was purchased from Sigma-Aldrich USA, a division of Merck.
Other studies of walnut leaf extracts for diabetic symptoms in humans have given mixed results. The authors of the current study point to the difficulty of identifying a suitable placebo. Toast powder may increase blood sugar, confounding collected data. Pressed tablets are not adequately blinded because the experimental drug smells like walnut leaves.
The authors of this study attribute statistically significant weight loss, associated decrease in BMI, and reduction in systolic BP to intake of walnut leaf extracts. However, these conclusions are questionable since dietary intake and physical activity were not monitored during the eight-week study. Previous studies have shown that participants in clinical trials often change their behavior, particularly food intake and level of activity, during enrollment in health outcome studies. These data, previous in vivo and in vitro studies, as well as information on traditional use, suggest that the use of walnut leaf extracts for symptoms of diabetes is an area worthy of further research.
The authors declare no conflict of interest.
Rabiei K, Ebrahimzadeh MA, Saeedi M, Bahar A, Akha O, Kashi Z. Effects of a hydroalcoholic extract of Juglans regia(walnut) leaves on blood glucose and major cardiovascular risk factors in type 2 diabetic patients: a double-blind, placebo-controlled clinical trial. BMC Complement Altern Med. July 2018;18(1):206. doi: 10.1186/s12906-018-2268-8.