The effect of garlic extracts on glycated hemoglobin and fasting blood sugar in animal and human studies: A systematic review and meta-analysis

INTRODUCTION

Diabetes mellitus (DM) is a group of metabolic illnesses characterized by exorbitant blood glucose levels caused by the body’s inability to produce or use insulin.^[1] It is characterized by bouts of glucose intolerance and hyperglycemia as a result of impaired insulin action, inadequate insulin production, or diminished tissue insulin sensitivity.^[2,3] Uncontrolled diabetes frequently results in chronic hyperglycemia or elevated blood sugar, which is linked to long-term harm, dysfunction, and failure of different organs, particularly the eyes, kidneys, nerves, heart, and blood vessels.^[4] Improper treatment can cause serious issues that not only deteriorate the quality of life of patients but also increase treatment expenses. The aftermath of incorrect treatment can be quite severe, ranging from prolonged hospital stays to additional medical procedures, which can significantly increase the cost of health care for patients.^[5]

According to the International Diabetes Federation, there are currently 537 million diabetic patients worldwide between the ages of 20 and 79 years, with that figure expected to increase to 643 million by 2030 and 783 million by 2045.^[6] The most frequent causes of this growth are an increase in sedentary behavior, the consumption of foods high in calories, obesity, and a longer life expectancy.^[7] The percentage of patients with DM who have seen a physician is sharply increasing.^[8,9] The use of traditional plant medicines that control hyperglycemia and dyslipidemia and avoid diabetes-related problems has received much attention among the available therapeutic options, such as hypoglycemic medications and insulin therapy, which have drawbacks.^[10,11]

Due to its potentially lethal complications, DM can be more severe than other non-communicable diseases. Despite the development of a number of synthetic drugs, none of these substances have yet to fully recover. Accessible, non-toxic drugs are still needed because some synthetic compounds have major side effects when used repeatedly.^[12] Traditional remedies have long been recognized as reliable sources of medicine. These compounds are widely utilized globally, demonstrating that herbs are becoming an increasingly important component of contemporary and cutting-edge therapies.^[13] More than 21,000 medicinal plants have been recognized worldwide.^[14] There are more than 400 plants that can be used to cure diabetes. Although there are numerous herbal medicines available for the treatment of diabetes, only a small subset of these plants have been subjected to scientific and medical evaluation to determine their effectiveness.^[15]

Plant-based medications are often regarded to be less expensive, more safe, and have less side effects than synthetically manufactured pharmaceuticals.^[16] Garlic is regarded as a plant capable of efficiently lowering blood sugar levels when used in herbal therapy. Garlic, a member of the Liliaceae family, is extensively grown and has been shown to benefit human health. Because no antibiotics or pharmaceuticals were available around 1550 B.C., garlic was used to treat a range of epidemics such as typhus, dysentery, cholera, and influenza.^[17,18] It is also a nutraceutical spice rich in polyphenols and organosulfur that has been utilized since antiquity. It has a variety of organic sulfur compounds, amino acids, vitamins, and minerals.^[19-21]

The primary volatile sulfur compounds include alliin, allicin, diallyl disulfide (DADS), diallyl trisulfide (DATS), diallyl sulfide, S-allyl cysteine (SACS), ajoene, and allyl mercaptan, which are the active components of garlic that are considered responsible for its health benefits DM. Allicin, SACS, and DADS are examples of garlic constituents that have therapeutic effects on insulin, lipid profiles, and serum glucose levels.^[22] In animal studies, garlic has been demonstrated to improve metabolic syndrome and insulin sensitivity.^[23]

A clinical trial on the impact of raw garlic on type 2 diabetic patients revealed a significant decrease in blood sugar levels and improvements in lipid metabolism and superoxide dismutase, catalase, and glutathione peroxidase levels in the erythrocytes of diabetic patients.^[24] The therapeutic benefits of garlic and garlic extracts in the treatment of individuals with diabetes and related metabolic disorders have been shown in studies in animal models and in preliminary human trials. There are some reviews done on garlic antidiabetic effects. However, most studies lack comprehensive quantitative analysis on fasting blood sugar (FBS) and glycated hemogobin (HbA1c) as well as did not include both animal and human studies together. Considering the evidence related to the effects of garlic extracts, it is highly recommendable to systematically analyze these effects. Thus, the aim of this study was to investigate the antihyperglycemic effects of garlic to reach comprehensive conclusions through a systematic review and meta-analysis.

MATERIALS AND METHODS

RESULTS

Characteristics of the included studies

A total of 6,867 study articles were found through the use of electronic databases, registers, and other search methods [Figure 1], which were updated and analyzed using ShinyApp to construct PRISMA 2020 flow diagrams.^[28,29] By removing duplicates and unconnected entries manually and automatically via the PRISMA 2020 online application, the total number of articles was reduced to 542; after thorough abstract and title screening, 56 papers remained. Following additional full-text screening and article exclusion with the addition of 32 previous studies, a total of 43 articles (16 trials and 27 in vivo) were included in the review.

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Figure 1:

Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 flow diagram for screened, excluded, and included studies. FBS: Fasting blood sugar.

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Four publications were excluded for failing to disclose doses, three for lacking blood glucose readings, nine for having unrelated indications, seven for lacking a control group, nine for failing to indicate interventions, five for being only short reports, five for being database duplicates, and three for having only abstracts. Both experiments yielded funnel plots, which are graphical representations of trial size plotted against the reported effect size; as trial size increases, trials are likely to converge around the true underlying effect size. In addition, the three funnel plots created, show that there is a more symmetrical plot, as the studies resemble each other in the 95% confidence interval (CI), which indicates there is less likelihood of publication bias for the studies analyzed [Figures 2-4]. The outcomes were verified by the effect measure using the inverse variance statistical method, the random effects analysis model, and the standard mean difference for the synthesis or presentation of results.

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Figure 2:

Funnel plots for in vivo studies with pseudo 95% confidence limits indicating the graphical representation of the size of the experiments plotted against the effect size. SE: Standard Error, SMD: Standard mean difference or Cohen’s d. Dotted line represents confidence interval and circles represent individual studies.

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Figure 3:

Funnel plots for clinical studies with pseudo 95% confidence limits that indicate a graphical representation of the size of trials plotted against the effect size for fasting blood sugar. SE: Standard Error, SMD: Standard mean difference or Cohen’s d. Dotted line represents confidence interval and circles represent individual studies.

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Figure 4:

Funnel plots for clinical studies with pseudo 95% confidence limits that indicate a graphical representation of the size of trials plotted against the effect size for HbA1c. SE: Standard Error, SMD: Standard mean difference or Cohen’s d. Dotted line represents confidence interval and circles represent individual studies.

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In vivo studies

Of the 27 in vivo studies analyzed in this systematic review and meta-analysis, 17 employed type 1 DM, 9 used type 2 DM experimental procedures, and 1 study did not define the type of DM. Five experimental studies were performed on mice,^[30-34] twenty studies were performed on rats,^[35-54] and two studies were performed on rabbits.^[55,56] The in vivo trials were performed on 448 study animals with durations ranging from acute effects of up to 16 weeks and dosages of garlic extract ranging from 20 mg/kg to 500 mg/kg [Table 2].

Table 2: Summary of in vivo studies.

References	Diabetes induction	Animals	DM induced	Duration	Dosage preparation	Garlic dose used	Route of administration
Bhattacharya et al.[30]	Alloxan	Mice	I	6 days	AGE (NO generating protein)	400 mg/kg	I.P.
Zhai et al.[31]	DIO	Mice	II	8 weeks	S-allyl-cysteine sulfoxide	200 mg, 500 mg/kg	I.P.
Hattori et al.[32]	KK-A (y)	Mice	II	8 weeks	Ajoene (derived from garlic)	Diet containing Ajoene 0.05%	Oral
Kumar and Reddy[33]	Alloxan	Mice	I	4 weeks	Ethanol garlic extract	45 mg/kg	I.P.
Swanston-Flatt et al.[34]	STZ	Mice	I	40 days	Bulb of garlic	1000 mg garlic in 400 mL water	Oral
Peng and Hu[35]	STZ	Rat	I	7 weeks	Aqueous garlic extract	500 mg/kg	I.P.
Thomson et al.[36]	STZ	Rat	II	8 weeks	Aged garlic extract	100 mg, 300 mg, 600 mg/kg	Oral
Shiju et al.[37]	STZ	Rat	I	12 weeks	Aged garlic extract	500 mg/kg	Oral
Hfaiedh et al.[38]	Alloxan	Rat	II	4 weeks	Fresh garlic extract	300 mg/kg	I.P.
Madkor et al.[39]	STZ	Rat	I	28 days	Garlic bulb powder	20 mg/kg	Oral
Saravanan and Ponmurugan[40]	STZ	Rat	I	45 days	S-allyl cysteine	150 mg/kg	Oral
Saravanan et al.[41]	STZ	Rat	I	45 days	S-allyl cysteine	150 mg/kg	Oral
Younis et al.[42]	Fructose, CRDH	Rat	II	60 days	S-allyl- mercapto- captopril	53.5 mg/kg	I.P.
Nasim et al.[43]	Alloxan	Rat	I	5 weeks	Alliin component of garlic	500 mg/kg	Oral
Hosseini et al.[44]	STZ	Rat	I	8 weeks	Aqueous garlic extract	100 g in 100 mL 0.9% saline solution	Oral
Jalal et al.[45]	High Fructose-fed	Rat	II	8 weeks	Aqueous garlic extract	500 mg/kg	I.P.
Eidi et al.[46]	STZ	Rat	I	14 days	Garlic ethanol extract	100 mg, 250 mg, and 500 mg/kg	Oral
Thomson et al.[47]	KK-A (y)	Rat	NS*	4 weeks	Raw garlic extract	500mk/kg	I.P.
Liu et al.[48]	STZ	Rat	I	16 weeks	GO and DADS	GO 100 mg/kg, DADS 40/80 mg/kg	Oral
El-Demerdash et al.[49]	Alloxan	Rat	I	4 weeks	Garlic juice	100 mg/kg	Oral
Liu et al.[50]	STZ	Rat	I	3 weeks	GO and DATS	GO 100 mg/kg, DATS 40 mg/kg	Oral
Jelodar et al.[51]	Alloxan	Rat	I	2 weeks	Garlic methanol extract	12.5% garlic in diet	Oral
Sheela and Augusti[52]	Alloxan	Rat	I	4 weeks	S-allyl cysteine sulfoxide	200 mg/kg	I.P.
Okorie et al.[53]	Alloxan	Rat	II	21 days	Mixed extracts with garlic	300 mg/kg	Oral
Susanti et al.[54]	STZ	Rat	II	14 days	Single clove garlic extract	50 mg, 75 mg, 125 mg/kg	Oral
Jain and Vyas[55]	Alloxan	Rabbit	I	Acute Effect	Ethyl and petroleum ether extract	0.25 mg/kg	I.P., Oral
Nasri[56]	Alloxan	Rabbit	II	Acute Effect	Aqueous garlic extract	250 mg, 300 mg and 350 mg/kg	Oral

STZ: Streptozotocin, NS*: Not stated, DIO: Diet-induced obesity, I.P.: Intraperitoneal, CRDH: Cohen-Rosenthal diabetic hypertensive, GO: Garlic oil, DATS: Diallyl Trisulfide, AGE: Aged garlic extract, NO: Nitric oxide, DADS: Diallyl Disulfide, KK-A(y): A mouse with cross between diabetic KK (Kasukabe-derived mouse) and agouti or lethal yellow A(y) mice.

A total of 27 in vivo studies involving 448 animals reported data on blood sugar levels from their experimental procedures. Seventeen studies used oral routes, nine studies used I.P. routes, and one study employed both oral and I.P. routes of administration. The extracts used in the study were ethanol extracts, fresh garlic extracts, aqueous garlic extracts, aged garlic extracts, ethyl ether extracts, petroleum ether extracts, and methanol extracts. The forest plot diagram shows that the I² values are heterogeneous among the included studies. For all outcome indicators of the studies, the I² value showed significant heterogeneity. When sensitivity analyses were performed by excluding outlier trials from the pooled studies, the degree of heterogeneity ranged from moderate to high. Thus, the pooling technique was based on the random effects model. The in vivo study results suggested that garlic significantly improved the FBS of diabetic animals compared with that of the placebo group (SMD = -1.32; 95% CI [-1.74, -0.89], P < 0.00001) [Figure 5].

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Figure 5:

Forest plot results for the effects of garlic on the change in fasting blood sugar (mg/dL) in the experimental and control comparison groups for animal (in vivo) studies. Small green squares represent the effect size of individual studies, the horizontal lines extending from the squares represent the CI for those studies, and a black diamond at the bottom represents the pooled effect size and its CI from the meta-analysis. SD: Standard deviation, Std.: Standard, IV: Inverse variance, df: Degrees of freedom, CI: Confidence interval, Tau: Kendall’s Tau is a tool to determine degree of association between two ordinal variables, Chi: Chi-square test to determine association of two nominal variables, P: Probability value, I²: Percentage of variation among studies caused by heterogeneity, Z: Standard score.

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Clinical studies

A total of 16 trials recruiting 843 subjects reported data on FBS concentrations. The duration of the 16 clinical studies on diabetic patients ranged from 10 days to 3 months, with various doses and preparation levels. Twelve studies revealed a substantial decrease in blood sugar levels,^[57-69] while four studies showed no significant decrease in blood sugar levels.^[59,70-72] For the effects of garlic on blood sugar levels, a minimum dose of 8.5 mg per day and a maximum dose of 3 g per day were utilized [Table 3].

Table 3: Summary of clinical studies.

References	Study design	Preparation type	Study participants
			Male	Female	Garlic
Mirunalini et al.[24]	Parallel	Garlic combination*	40	0	20
Parham et al.[57]	Parallel	Garlic tablet, allicor	16	48	33
Choudhary et al.[58]	Open label	Garlic with metformin	15	25	20
Sukandar et al.[60]	Parallel	AGE	Not Stated	17
Kumar et al.[61]	Open label	Garlic with metformin	Not Stated	30
Chhatwal et al.[62]	Open label	Ethyl acetate extract	Not Stated	30
Ashraf et al.[63]	Open label	Garlic tablet	33	27	30
Mahmoodi et al.[64]	Open label	Raw garlic	53	32	45
Sobenin et al.[65]	Parallel	Garlic with turmeric	26	34	30
Li et al.[66]	Parallel	Garlicin	Not Stated	13
Zhang et al.[67]	Parallel	Garlic oil and allicin	27	33	39
Bordia et al.[70]	Parallel	AGE	Not Stated	30
Ali and Thomson[71]	Open label	Fresh garlic	8	0	4
Jain et al.[72]	Parallel	Garlic powder	19	23	20
Afarid et al.[73]	Parallel	Garlic tablet	63	28	45
Ghorbani et al.[74]	Parallel	Crushed raw garlic	Not Stated	25
References	Study participants		Duration of study	Garlic dose used in the study	Route of administration
	Placebo	Mean age
Mirunalini et al.[24]	20	Not Stated	12 weeks	750 mg/day	Oral
Parham et al.[57]	31	48.2±2.6	4 weeks	300 mg BID	Oral
Choudhary et al.[58]	20	53.8±12.2	12 weeks	250 mg garlic/day	Oral
Sukandar et al.[60]	12	57.5±3.7	12 months	2400 mg/day	Oral
Kumar et al.[61]	30	53.3±11.6	12 weeks	250 mg garlic/day	Oral
Chhatwal et al.[62]	30	45.3±7.6	3 months	1 g raw garlic/day	Oral
Ashraf et al.[63]	30	40.11±5.04	24 weeks	300 mg TID	Oral
Mahmoodi et al.[64]	40	44.47±7.57	42 days	10 g/day	Oral
Sobenin et al.[65]	30	53.12±2.11	12 weeks	2.4 g/day	Oral
Li et al.[66]	21	49.8±9.23	10 days	64 mg/kg	I.V. drip
Zhang et al.[67]	21	27.5±2.1	11 weeks	8.2 mg, 7.8 mg/day	Oral
Bordia et al.[70]	30	Not Stated	4 weeks	1200 mg/day	Oral
Ali and Thomson[71]	4	40.2±5.8	16 weeks	3 g/day	Oral
Jain et al.[72]	22	52±12	12 weeks	900 mg/day	Oral
Afarid et al.[73]	46	59.5±8.25	4 weeks	500 mg/day	Oral
Ghorbani et al.[74]	25	58.24±6.38	4 weeks	100 mg/kg	Oral

*Garlic 10%, nettle 20%, berry 10%, fenugreek 20%, walnut 20%, and cinnamon 10%, RCT: Randomized control, trail, AGE: Aged garlic extract, TID: Ter in die (three times a day), BID: Bis in die (two times a day)

The I² values showed that there was heterogeneity among the studies. A priori group analysis and sensitivity analysis were carried out to determine the potential cause of heterogeneity in these trials. For all outcome indicators, the I² values demonstrated significant heterogeneity among the studies. Similar to the in vivo studies, when sensitivity analyses were performed by excluding outlier trials from the pooled studies, the degree of heterogeneity ranged from moderate to high. As a result, the pooling technique was based on the random effects model. The results suggested that garlic significantly improved FBS compared with the placebo (SMD = -1.37; 95% CI [-1.87, -0.87], P < 0.00001) [Figure 6]. Although only six studies^{[57,60-62,64,73]} reported the effect of garlic on HbA1c, the pooled analysis of their findings indicated that garlic significantly improved the HbA1c of clinical study subjects (SMD = -2.98; 95% CI [-4.71, -1.25], P < 0.00001) [Figure 7].

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Figure 6:

Forest plot results for the effects of garlic on the change in fasting blood sugar (mg/dL) in the experimental and placebo comparison groups in clinical studies. Small green squares represent the effect size of individual studies, the horizontal lines extending from the squares represent the CI for those studies, and a black diamond at the bottom represents the pooled effect size and its CI from the meta-analysis. SD: Standard deviation, Std.: Standard, IV: Inverse variance, df: Degrees of freedom, CI: Confidence interval, Tau: Kendall’s Tau is a tool to determine degree of association between two ordinal variables, Chi: Chi-square test to determine association of two nominal variables, P: Probability value, I²: Percentage of variation among studies caused by heterogeneity, Z: Standard score.

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Figure 7:

Forest plot results for the effects of garlic on the change in HbA1c in the experimental and placebo comparison groups for clinical studies. Small green squares represent the effect size of individual studies, the horizontal lines extending from the squares represent the CI for those studies, and a black diamond at the bottom represents the pooled effect size and its CI from the meta-analysis. SD: Standard deviation, Std.: Standard, IV: Inverse variance, df: Degrees of freedom, CI: Confidence interval, Tau: Kendall’s Tau is a tool to determine degree of association between two ordinal variables, Chi: Chi-square test to determine association of two nominal variables, P: Probability value, I²: Percentage of variation among studies caused by heterogeneity, Z: Standard score.

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Phytochemical and antihyperglycemic activities

This systematic review revealed that the garlic phytochemicals that have antihyperglycemic effects include alliin, allicin, DADS, DATS, diallyl sulfide, SACS, and ajoene. The structure is listed below with the help of ChemDraw to construct the figures [Figure 8].

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Figure 8:

The structures of phytochemicals isolated from Allium sativum garlic. (1) Allicin, (2) S-allyl cysteine, (3) ajoene, (4) alliin, (5) diallyl sulfide, (6) diallyl disulfide, (7) diallyl trisulfide (ChemDraw) was used to construct the figures.

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DISCUSSION

The present study examined 43 articles on the effects of garlic on blood sugar levels in 27 animal models and 16 clinical investigations. The results of this systematic review and meta-analysis demonstrated that eating garlic significantly decreased FBS levels. Garlic may affect blood sugar levels in a variety of ways. It includes increasing the secretion of endogenous insulin, improving insulin sensitivity and insulin-like activity,^[20,50,74] reducing oxidative stress,^[23] enhancing beta-cells in the pancreas by promoting their regeneration,^[75] and possibly interfering with carbohydrate absorption through fibers.^[76] The majority of the articles revealed that, compared to diabetic controls, garlic and its constituents exhibited significant antihyperglycemic benefits. Studies conducted in animals revealed that garlic significantly reduced blood sugar levels, even when combined with aqueous extracts of Cymbopogon citratus and Annona muricata leaves.^[53,56] These studies indicated that the most efficient way to drastically decrease blood glucose levels was with a single clove garlic extract taken orally once a day at a dose of 125 mg/kg.^[54] Injection of a unique, isolated protein that produces nitric oxide from aqueous garlic extract dramatically lowered blood sugar levels in diabetic mice.^[30]

The most effective and active component of garlic, A. sativum, which has an antihyperglycemic effect of 0.25 mg/kg orally, was reported to be the ethyl ether extract of garlic, which was due to increased insulin-like activity.^[55,77] In vivo studies revealed that the remarkable blood glucose-lowering effects of ethanol or aqueous extracts, S-allyl-cysteine sulfoxide, SACS, diallyl sulfoxide, triallyl sulfoxide, and oil from A. sativum in healthy and streptozotocin (STZ)- and alloxan-induced diabetic rats, mice, or rabbits are mediated by the stimulation of insulin secretion from parietal cells.^[35,43,49] According to different studies, a number of recent studies evaluating the impact of garlic on FBS levels have been published. We revisited the topic of garlic’s impact on blood glucose for several reasons. The severity of diabetes and the participants’ initial blood sugar levels were factors, as researchers have examined how garlic juice or extracts affect oral glucose tests in normal and alloxan-DM rabbits.^[56,78,79]

All garlic formulations improved the oral glucose test in both normal and diabetic mice and decreased FBS. In contrast, allicin reduced the FBS concentration and increased the oral glucose concentration in rats with mild but not severe alloxan-induced diabetes, but had no effect on the FBS concentration in control rats. It has been proposed that garlic’s ineffectiveness at decreasing FBS concentrations in normal animals may be due to their capacity to maintain normal blood sugar homeostasis.^[80-82] The residual beta-cell mass in the model used, however, was too low to provide high enough basal insulin concentrations to demonstrate improvements in glucose clearance at a first-order rate, which is thought to have caused the ineffectiveness of garlic in lowering an abnormally high FBS level in diabetes patients. Because various garlic preparations contain various compounds, the type of garlic used in these trials and how it was prepared are both crucial. The temperature, preparation time, and extraction solvents are only a few of the processing variables that have a large impact on the chemical makeup of a garlic product.^[44,83,84]

Clinical trials revealed that herbal mixtures, including A. sativum, were effective at reducing insulin resistance and blood sugar levels in people with advanced type 2 diabetes^[57] and daily oral administration of 100 mg/kg garlic extract lowered plasma glucose levels.^[58] A few recent studies have also shown that garlic can lower lipid profiles, glucose parameters (FBS levels),^[83,84] and hemoglobin A1c (HbA1c) in diabetic patients.^[85] According to some research, using the antidiabetic medication metformin at a dosage of 500 mg twice daily and the herb garlic at a dosage of 300 mg three times daily for 24 weeks may have greater potential for managing diabetes patients by lowering blood glucose levels and other parameters.^[63] Through lowering fasting blood glucose levels via HbA1c, double-blind clinical research in diabetic patients revealed that garlic herbal medicine at 750 mg 3 times per day for 12 weeks had potential effects on the management of diabetes.^[57]

These studies demonstrated the potential of garlic in the care of diabetic patients by lowering fasting blood glucose levels as well as other indicators, such as total cholesterol, low-density lipoprotein, triglycerides, and hyperlipidemia.^{[58,59,63,65]} Six clinical studies have reported the effect of garlic consumption on HbA1c.^{[57,60-62,64,73]} The pooled effect analysis of the study showed that garlic significantly improved the level of HbA1c with long-term intervention. The effects of garlic on glycemic control have been investigated in the current meta-analysis in both animal studies for FBS and clinical trials for FBS and HbA1c. The examination of solely randomized, controlled clinical trials and the impartial evaluation of trial quality are additional strengths of the current study.

Garlic decreases fasting blood glucose levels in both animal and human trials, according to the findings of this systematic review and meta-analysis. Although traditional diabetes medications can be used as antihyperglycemic agents, some diabetic patients cannot take them because of significant side effects. As a result, people with minor increases in serum glucose who are unable to tolerate pharmaceutical drugs may realize that consuming garlic is a safe and beneficial alternative. Despite these promising results, more clinical studies, as well as consistency in the techniques used to manufacture extracts, the duration of interventions, and the standards established for research design, are still needed to acquire accurate data.

CONCLUSION

The findings of this systematic review and meta-analysis show that garlic lowers fasting blood glucose levels in both animal and human trials. Although standard diabetes therapies can be used as antihyperglycemic agents, some diabetic patients are unable to take them due to adverse side effects. As a result, those with minor elevations in serum glucose who are unable to handle pharmaceutical medications may discover that eating garlic is a safe and beneficial option. Despite the encouraging results, it has been stressed that additional clinical trials, as well as consistency in the procedures used to create extracts, the duration of interventions, and the standards established for research design, are still required to collect correct data.