Reviewed: Anh NH, Kim SJ, Long NP, et al. Ginger on human health: A comprehensive systematic review of 109 randomized controlled trials. Nutrients. January 2020;12(1). doi: 10.3390/nu12010157.
Ginger (Zingiber officinale, Zingiberaceae) root traditionally has been used to relieve common gastrointestinal (GI) issues, including abdominal pain, nausea, and vomiting. Some studies have shown that the anti-emetic properties of ginger may be an effective treatment for motion sickness, post-operative nausea, and chemotherapy-induced nausea and vomiting (CINV). This systematic review aimed to summarize the effects of oral ginger consumption on any clinically studied aspect of human health, provide direction for future clinical research, and discuss the shortcomings of the available randomized controlled trials (RCTs).
Four English and two Korean databases were searched through July 2019: PubMed, EMBASE, Cochrane Central Register of Controlled Trials, Clinical Trials, Korean Studies Information Service System (KISS), and National Digital Science Library (NDSL) of Korea. RCTs investigating the efficacy of ginger on human health and disease were included. After excluding ineligible articles (e.g., duplicates, case reports, commentaries, reviews, etc.), a total of 109 articles were included in this systematic review and organized into six subsections: anti-emetic (n = 47), GI (n = 12), analgesic (n = 16), anti-inflammatory (n = 8), metabolic improvement (n = 16), and others (n = 10).
Most of the included RCTs had a sample size of less than 60 participants. The effects of ginger were assessed using various controls, including placebo (n = 73), medications or other functional materials (n = 14), both placebo and medication or other functional materials (n = 16), or no treatment (n = 6). Ginger was administered in daily doses that typically ranged from 500 mg to 1,500 mg. More than half of the studies were conducted in Iran or the United States.
Of the 47 RCTs that evaluated the anti-emetic effects of ginger, 16 studies investigated CINV. Eight demonstrated a positive effect of ginger on the prevention or alleviation of CINV as well as reduction of acute and delayed CINV in both children and adults.
Hyperemesis, or nausea and vomiting of pregnancy (NVP), was evaluated in 14 RCTs. Eight studies compared ginger to a placebo, demonstrating significant effects in the ginger group (P value not given). In general, ginger showed similar effects when compared to other medications including dimenhydrinate and metoclopramide.
Post-operative nausea and vomiting (PONV) was evaluated in 11 RCTs. Five showed no significant benefits using ginger to treat PONV. One study demonstrated ginger’s effectiveness in treating nausea and vomiting induced by antiretroviral therapy (P = 0.001).
Ginger also was assessed for its protective effects on the GI system. Seven RCTs studied gastric function, mainly gastric emptying and gastric dysrhythmia (abnormal frequency of gastric contractions). Ginger was reported to enhance gastric emptying. Ginger proved beneficial in the prevention of slow-wave gastric dysrhythmias induced by acute hyperglycemic events (P < 0.05).
Four RCTs evaluated the risk of colorectal cancer, and there were mixed results with the ginger treatments. Ginger was shown to have a beneficial effect on colorectal cancer by reducing tumorigenic risk factors; however, there was no difference in these risk factors between the ginger and placebo groups for those with average risk of colorectal cancer.
One study determined no difference between the ginger and placebo groups in reducing the symptoms of irritable bowel syndrome.
Seven RCTs examined the analgesic effects of ginger on primary dysmenorrhea. Four compared ginger to other medications (e.g., mefenamic acid and ibuprofen) and found similar efficacy between the two groups. Three trials compared ginger to a placebo and measured the decrease in pain using a visual analog scale. These studies reported contradictory results, with two studies in favor of ginger and the other reporting no difference between the groups.
Four RCTs evaluated muscular pain. Two of these studies indicated a lack of evidence supporting ginger’s effect on muscular pain, and two reported that ginger partially relieved muscular pain when compared to placebo.
Migraines and headaches were studied in three RCTs that reported significant differences in symptom attenuation (P < 0.05 for all). Two studies demonstrated that ginger may be beneficial for reducing low back and chest pain associated with transluminal coronary angioplasty (a procedure used to open blocked coronary arteries).
Eight RCTs evaluated the anti-inflammatory effects of ginger in arthritis-related diseases, particularly osteoarthritis (OA). Six studies reported that ginger consumption improved symptoms of OA when compared to placebo. Additional studies demonstrated potential pain reduction with ginger supplementation in patients diagnosed with OA and rheumatoid arthritis.
Ginger was assessed in patients with type 2 diabetes mellitus (T2DM) and obesity. Five studies evaluated the effects of ginger on diabetes-related indices including glycemic markers, lipid levels, and blood pressure. Ginger supplementation did not have a significant effect on blood pressure in T2DM, and only minimally reduced weight in obese women.
Four studies examined conditions related to obesity including cardiovascular disease, serum adipocytokines, and breast cancer. Among these studies, three demonstrated that ginger had a positive effect on fasting blood sugar, hemoglobin A1c (HbA1c), insulin sensitivity, and insulin resistance.
In terms of obesity and cardiovascular health, ginger was beneficial in lowering risk factors including body fat mass, body fat percentage, total cholesterol, waist circumference, waist-to-hip ratio, and insulin resistance. Ginger may have antioxidant and anti-dysmetabolic effects in obese women diagnosed with breast cancer. Additional studies showed that ginger may reduce risk factors of metabolic syndrome.
The authors also reviewed RCTs that evaluated the use of ginger for thermoregulatory, thrombotic, and respiratory functions. Ginger demonstrated mixed results for thermoregulatory function (maintaining normal body temperature). However, ginger may reduce the use of mechanical ventilation and length of stay in intensive care in patients diagnosed with acute respiratory distress syndrome (ARDS) and asthma.
Two studies reported little to no effect of ginger on thrombotic reaction (blood clot formation). However, one study using a single dose of 10 g powdered ginger showed a significant reduction in adenosine diphosphate-induced and epinephrine-induced platelet aggregation in patients recovering from myocardial infarction (P value not given).
Ginger was shown to significantly reduce menstrual bleeding in teenagers aged 15 to 18 years (P < 0.001). Another study showed that ginger significantly increased milk volume on the third day postpartum compared to placebo (P < 0.01).
Adverse Events and Study Quality
Only 17 studies reported adverse events. Heartburn was reported in 16 studies in which participants received a daily dose between 500 mg and 2,000 mg of ginger. The remaining side effects were not conclusively assigned to ginger due to small sample size. GI-related side effects included heartburn, nausea, abdominal pain, bloating, gas, and epigastric distress. Diarrhea was reported in two studies that evaluated heavy menstrual bleeding after elective cesarean section. Patients that underwent laparoscopic surgery reported cardiovascular and respiratory symptoms with ginger treatment.
The majority of the studies did not describe the blinding of assessors or methods for random sequence generation and allocation concealment, and fewer than half of the studies were classified as having a low risk for selection and detection biases. Most of the studies were classified as having a low risk of performance, attrition, and reporting biases, with 101 and 103 studies assigned to low risk of attrition and reporting bias, respectively. Using the Cochrane Collaboration’s quality assessment tool, only eight studies were assessed as having a low risk for every type of bias.
The majority of RCTs evaluating the efficacy of ginger on human health focused on nausea and vomiting, GI function, pain, inflammation, metabolic syndrome, and other symptoms. Most of the studies showed that ginger had a positive outcome on the selected measure, especially those studies that evaluated NVP, digestive function, markers for colorectal cancer risk, and anti-inflammatory functions. Limitations include relatively small sample sizes, inconsistent evaluation systems or parameters, and general quality of the trials. The authors recommend that future research include detailed descriptions of the methodology and a sufficient pool of participants to address the functional characteristics of ginger.