Effectiveness of royal jelly supplementation in glycemic regulation: A systematic review

Table 1 Human trials examining acute effects of royal jelly treatment

Ref.	Study design	Subjects	Treatment	Outcome measures	Effectiveness
Iaconelli et al[24]	Crossover study	N = 10 + 10 healthy individuals and individuals with type 2 diabetes	Each subject went through three studies on different days: 0 g, 12 g, or 23 g of sebacic acid substituted fats in a meal	Glucose clearance: Postprandial	Significantly improved glucose clearance in diabetic subjects only in dose-dependent manner (d = -1.70)
				Insulin secretion/clearance rate	Significantly improved GLUT4 expression (d = 0.81) and glucose uptake in L6 cells (d = 0.67)
				GLUT4 expression in L6 myotube cells	Insulin secretion/clearance decreases significantly in similar fashion between healthy and diabetic patients. Dose-response relationship. For diabetics, d = -1.12
Mobasseri et al[25]	Randomized controlled trial	N = 20 + 20 adults with type 2 diabetes aged 30-65 in control and treatment groups	15 g of royal jelly ingested orally after overnight fasting	Hyperglycemia: Fasting blood glucose, glucose clearance after royal jelly consumption	No significant difference in outcome measures between two groups
				Hyperinsulinemia: Serum c-peptide and insulin
Münstedt et al[26]	Controlled trial	N= 10 + 10 healthy males, split into experimental and control groups	20 g of fresh royal jelly ingested orally	Glucose clearance: Plasma samples during OGTT	Significantly increased rate of glucose clearance (insufficient information for effect size calculation)
				Insulin resistance: Serum insulin and c-peptide	No significant change in serum insulin profile
Münstedt et al[27]	Randomized controlled trial	N = 15 healthy male adults aged 20-34, unspecified distribution between treatment and control groups	0.55 g lyophilized royal jelly in enteric-coated capsule ingested orally	Hyperglycemia: Glucose clearance (OGTT)	Improved glucose clearance and decreased plasma insulin, unspecified statistical significance (insufficient information for effect size calculation)
				Insulin resistance: Serum insulin and c-peptide

OGTT: Oral glucose tolerance test; GLUT4: Glucose transporter type 4.

Table 2 Human trials examining effects of long-term royal jelly treatment

Ref.	Study design	Subjects	Treatment	Outcome measures	Effectiveness
Khoshpey et al[12]	Randomized double-blind controlled trial	N = 11 females + 12 males aged 20-65 with type 2 diabetes in control group (placebo)	3000 mg royal jelly oral capsules once per day for 8 wk. Control received placebo	Macronutrient intake	No significant change in macronutrient intake
		N = 13 females + 10 males aged 20-65 with type 2 diabetes in treatment group		Hyperglycemia: Fasting blood glucose	Fasting blood glucose significantly reduced in comparison to control group (d = -0.87)
Mobasseri et al[28]	Randomized controlled trial	N = 25 + 25 females with type 2 diabetes aged 30-65 in control and treatment groups	200 mg royal jelly powder prepared in gel form and served with breakfast for 8 wk. Control group received placebo	Plasma triglyceride	Significantly decreased plasma triglyceride in comparison to control (d = -0.476)
Morita et al[29]	Randomized double-blind controlled trial	N = 30 healthy adults 42-83 yr of age in control (placebo)	3000 mg royal jelly in 100 mL liquid daily for 6 mo. Control received placebo identical in appearance	Body weight: BMI	Significantly improved fasting blood glucose (d = -0.9596)
		N = 31 healthy adults 42-83 yr of age in treatment group		Insulin resistance: HOMA-IR	No significant changes in other outcomes of interest
				Hyperglycemia: HbA1c, fasting blood glucose
				Plasma triglyceride
Pourmoradian et al[13]	Human double-blinded randomized clinical trial	N = 23 females aged 30-65 with type 2 diabetes in treatment group	1000 mg lyophilized royal jelly in soft gel form served after breakfast for 8 wk. Control group received placebo soft gel	Body weight: weight scale before and after study period	Significantly decreased body weight within same group, before and after intervention (d = -0.3808)
		N = 22 females aged 30-65 with type 2 diabetes in control group		Macronutrient intake: 24-h recall food questionnaire for 3 d before and after study period	Significantly decreased energy intake within same group, before and after intervention (d = -9.52)
Pourmoradian et al[30]	Human double-blinded randomized controlled trial	N = 21 females aged 30-65 with type 2 diabetes in treatment group	1000 mg lyophilized royal jelly in soft gel form served after breakfast for 8 wk. Control group received placebo soft gel	Plasma insulin	Significantly decreased plasma insulin and HbA1c and insignificantly decreased fasting blood glucose compared to baseline within same group, before and after intervention.
		N = 20 females aged 30-65 with type 2 diabetes in control group		HbA1c	d = 0.016 (HbA1c)
				Hyperglycemia: Fasting blood glucose	d = -0.0785 (plasma insulin)
Shidfar et al[31]	Human double-blinded randomized controlled trial	N = 23 + 23 adults 25-65 yr old with type 2 diabetes in experimental and control (placebo) groups	1000 mg royal jelly in soft gelatin capsules 3 times daily for 8 wk. Control group received placebo identical in appearance to treatment	Fasting blood sugar	Significantly decreased fasting blood levels to more normal range (d = -0.3725)
				Macronutrient intake: 24-h recall diet questionnaire	Did not significantly alter macronutrient intake
				Insulin resistance: HOMA-IR	Significantly decreased HOMA-IR: improved insulin sensitivity (d = -0.79)

RJ: Royal jelly; HOMA-IR: Homeostatic model assessment of insulin resistance; BMI: Body mass index; HbA1c: Hemoglobin A1c.

Table 3 Animal and in vitro trials examining effects of long-term royal jelly treatment

Ref.	Study design	Subjects	Treatment	Outcome measures	Effectiveness
Ghanbari et al[14]	Randomized controlled trial	N = 8 healthy male Wistar rats aged 10-12 wk (control)	100 mg/kg BW royal jelly dissolved in 1 mL of water daily for 6 wk	Hyperinsulinemia: ELISA test on plasma sample	Treatment significantly improved insulin levels (d = 1.67) and hyperglycemic fasting blood glucose (d = -2.72) levels to levels similar to healthy control group
		N = 8 diabetic male Wistar rats aged 10-12 wk		Hyperglycemia: Fasting plasma glucose
		N = 8 healthy male Wistar rats aged 10-12 wk receiving treatment
		N = 8 diabetic male Wistar rats aged 10-12 wk receiving treatment
Fujii et al[32]	Controlled trial	N = 80 male streptozotocin-diabetic rats aged 5 wk equally split into three experimental groups and one control group	Each experimental group had one of 1, 10, and 100 mg/kg body weight royal jelly administered orally by force for 4 wk. Control group received purified water	Hyperglycemia: Blood glucose (unknown whether fasting)	Royal jelly administration overall slightly decreased blood glucose levels in non-dose dependent manner (no information on statistical significance)
				Body weight	No significant change in body weight between groups
Membrez et al[33]	Randomized controlled trial	N = 15 male db/db mice aged 6-8 wk in control group	1 g/kg body weight of sebacic acid was added to chow food in one experimental group, and 10 g/kg body weight SA to second experimental group’s chow for 6 wk	Hyperglycemia: OGTT and fasting (plasma samples)	In more heavily supplemented group: Hyperglycemia significantly improved (d = -1.86) and improved glucose clearance (d = -3.20), HbA1c significantly decreased (d = -1.89), ketone bodies significantly increased (d = 1.16), dose response relationship observed, gluconeogenic and lipogenic enzyme expression significantly decreased (insufficient information for SMD estimation), food intake was significantly decreased (d = -1.82).
		N = 30 male db/db mice aged 6-8 wk equally split in two experimental groups		HbA1c: Plasma samples
				Liver gene expression: RNA extracted from liver samples
				Food intake: Chow consumed
Takikawa et al[7]	In vitro	L6 myotubes grown in cell culture and collected from healthy male mice 7 wk of age	Cell cultured myotubes treated with 10H2DA	Glucose clearance: GLUT4 translocation to plasma membrane	Significantly improved GLUT4 translocation to plasma membrane in skeletal muscle cells compared to non-treated myotube cells (d = 0.4698)
			Mice fed 1.6 mmol/kg 10H2DA
Yoneshiro et al[34]	Controlled trial	N = 8 3-wk old healthy male mice (control)	High fat diet with 5% lyophilized royal jelly powder for 17 wk	Body weight gain	Body weight gain due to white adipose tissue significantly reduced compared to HFD group (d = -2.82)
		N = 11 3-wk old healthy male mice fed HFD		Hyperlipidemia: Plasma sample	Significantly decreased levels of NEFA compared to HFD (d = -1.6072)
		N = 11 3-wk old healthy male mice fed high fat diet with treatment		Hyperglycemia: Plasma sample	Significantly improved hyperglycemia compared to HFD group (d = -2.04)
				Insulin resistance: HOMA-IR	HOMA-IR significantly decreased compared to HFD group, not significantly different from control group (d = -1.23)
Zamami et al[15]	Controlled trial	N = 6 6-wk old healthy male Wistar rats (control, received water)	Two experimental groups: One fed 100 mg/kg and the other 300 mg/kg of dilute enzymatically treated royal jelly supplementation daily for 8 wk	Insulin resistance: HOMA-IR	High fructose diet induced insulin resistance in rats
		N = 5 6-wk old healthy male Wistar rats as vehicle-treated group (received high fructose consumption)		Food intake	Plasma insulin levels and HOMA-IR similar between healthy control group and fructose drinking rats supplemented with 300 mg/kg royal jelly. Dose dependent relationship observed d = -0.7063 (effect size of 300 mg/kg royal jelly on fructose drinking rats)
		N = 6 + 6 6-wk old healthy male Wistar rats (received high fructose consumption) in two treatment groups		Body weight	No significant difference in body weight and FBG between groups
				Plasma triglycerides	Plasma triglycerides significantly decreased compared to control dose-dependently (d = -1.62)
Watadani et al[35]	Controlled trial	N = 7 female KK-Ay mice 5 wk of age in control group	3 mg/kg 10H2DA for 4 wk	Hyperglycemia: Plasma glucose samples collected in intervals after OGTT	Significantly improved glucose clearance (d = -1.33) and fasting blood glucose (d = -1.23)
		N = 8 female KK-Ay mice 5 wk of age in treatment group		Body weight: Adiposity index of abdominal, mesenteric and retroperitoneal fat tissue	Body weight did not differ between groups
				Insulin resistance: HOMA-IR	Significantly improved insulin sensitivity (d = -4.44)
				Glucose regulatory proteins: AMPK, G6Pase, Pck1 levels, GLUT4, GS/GSK in tissue homogenates	Significantly increased levels of G6Pase (d = 1.22) and Pck1(d = 0.77) mRNA in liver cells. Significantly increased levels of pAMPK in muscle (d = 3.13), but no change in liver. Insignificant increase in GLUT4 in muscle cells. No change in GS/GSK levels between groups
Yoshida et al[36]	Controlled trial	16 female KK-Ay mice split into control and experimental groups	10 mg/kg royal jelly in 1/15M phosphate buffer 5 d/wk for 4 wk		Significantly improved rates of glucose clearance (d = -1.25)
					Insignificantly decreased body weight
					Significantly increased pAMPK levels in liver (d = 2.39) and skeletal muscle (d = 1.73). Significantly decreased G6Pase mRNA levels in liver (d = -1.65), but no change in Pck mRNA levels. Insignificantly increased GLUT4 levels in skeletal muscle
					Significantly decreased plasma NEFA (d = -1.42). No change in plasma TG
					No significant change in plasma insulin

GLUT4: Glucose transporter type-4; 10H2DA: 10-hydroxydecanonic acid; OGTT: Oral glucose tolerance test; HOMA-IR: Homeostatic model assessment of insulin resistance; GS(K): Glycogen synthase (kinase); AMPK: AMP-dependent kinase; NEFA: Non-esterified fatty acids; HFD: High fat diet.

Table 4 GRADE assessment for long-term effectiveness of RJ treatment on glycemic control

GRADE criteria	Rating	Support for judgement	Overall quality of evidence
Outcome: Long term glycemic control (n = 14 studies)
RoB (assessed on Cochrane RoB Collaboration Tool)	No	Only one study had low RoB for all categories. Most studies had at least one item at high or unclear RoB	High
	Serious (-1)1
	Very serious (-2)
Inconsistency	No	Generally, positive clinical effects demonstrated but some studies indicate null effects. There are also large variations in magnitude of effect. Heterogeneity is notable between the studies (in population, intervention and outcome assessment)	Moderate
	Serious (-1) 1
	Very serious (-2)
Indirectness	No1	Evidence synthesized from studies addresses review question with respect to population, interventions and outcome	Low1
	Serious (-1)
	Very serious (-2)
Imprecision	No	All studies have groups with small sample sizes (≤ 20), with no indication that they meet required sample sizes to detect difference in outcome; observable but statistically insignificant measures in many studies suggest sample sizes were too small to detect difference. 95% confidence intervals of effect size estimates mostly suggest an appreciable benefit for treatment, but there are several that suggest possibility of no meaningful effect	Very low
	Serious (-1)
	Very serious (-2) 1
Publication bias	Undetected1	There is chance of publication bias considering the review is entirely “small-scale” trials; this area of research is not well-established and there is potential for publication bias, but none was overtly detected
	Strongly suspected (-1)
Other	Large effect (+11 or +2)	Standardized mean difference of studies (effect size) indicates large magnitude of effect of treatment. Dose-response relationships observed
	Dose response (+11 or +2)
	No plausible confounding (+1 or +2)

¹Indicates decision. RoB: Risk of Bias. Adapted from Ryan and Hill[21] and Wei et al[22].

Table 5 GRADE assessment for acute effects of RJ administration on glycemic control

GRADE criteria	Rating	Support for judgement	Overall quality of evidence
Outcomes: Acute glycemic control outcomes (n = 4 studies)
RoB (assessed on Cochrane RoB Collaboration Tool)	No	Majority of studies had overall high RoB, likely affecting the study results	High
	Serious (-1)
	Very serious (-2)1
Inconsistency	No	Outcome effects are somewhat consistent, and studied population are similar enough to not be considered detrimental to evidence quality. Intervention, however, was heterogeneous across all relevant studies	Moderate
	Serious (-1) 1
	Very serious (-2)
Indirectness	No1	Research question is addressed by majority of the animal studies	Low
	Serious (-1)
	Very serious (-2)
Imprecision	No	All studies have groups with small sample sizes (≤ 20), with no indication that they meet required sample sizes to detect difference in outcome. For those with calculable effect sizes, the confidence intervals suggest potential for no appreciable benefit	Very low1
	Serious (-1)
	Very serious (-2) 1
Publication bias	Undetected1	There is chance of publication bias considering the review is entirely “small-scale” trials; this area of research is not well-established and there is potential for publication bias, but none was overtly detected
	Strongly suspected (-1)
Other	Large effect (+1 or +2)	Some dose response relationships observed, however not enough studies to confirm this relationship. Insufficient effect size estimates to determine if effect is large or not
	Dose response (+1 or +2)
	No plausible confounding (+1 or +2)

¹Indicates decision. RoB: Risk of Bias. Adapted from Ryan and Hill[21] and Wei et al[22].