A Systematic Review of Beta Cell Function in Adults of Black African Ethnicity

Table 1

Summary of characteristics of the included studies: methods, population of interest, glucose tolerance status, findings, and mNOS.

Study	Methods	Study design	Population of interest					Comparison population		Findings	mNOS
			Ethnicity		Mean age	Gender %M/F	Glucose tolerance
Rubenstein et al. [24]	OGTT	Cross-sectional	Native black South African, no FHx of T2D	7		100/0	NGT	White South African, no FHx of T2D	8	Similar fasting insulin levels, but lower serum insulin in response to oral glucose and lower renal insulin clearance in BA compared to WE	5
Shires et al. [25]	“Maximal beta cell stimulation”—75 g oral glucose followed by IV tolbutamide and glucagon stimulation	Cross-sectional	Obese native black South African	10		0/100	Nondiabetic	Obese white South African	8	Serum insulin and C-peptide levels significantly lower in BA compared to WE 30 mins after oral glucose and 30 mins after tolbutamide and glucagon	6
Cruickshank et al. [31]	OGTT	Cross-sectional	UK Afro-Caribbean	106	(F), (M)	50/50	NGT, IGT, and T2D	White European	101	No statistically significant difference between C-peptide and insulin concentrations post oral glucose; however, difference in profiles led investigators to suggest impaired hepatic processing of insulin in BA.	6
Osei et al. [48]	OGTT	Case control	African American (first-degree relatives of T2D and controls)	24 relatives and 8 controls	(relatives) and (controls)	0/100	NGT	White American (first-degree relatives of T2D and controls)	22	In both first-degree relatives and controls, iAUC insulin and C-peptide were significantly higher in BA compared to WE.	9
UK Prospective Diabetes Study Group [32]	Fasting glucose and insulin to derive HOMA%B	Prospective cohort	UK Afro-Caribbean	387	(M); (F)	57/43	T2D	UK Caucasian	4177	Lower HOMA%B in BA compared to WE, adjusted for age and BMI. BA had higher fasting plasma glucose and higher HbA1c vs. WE.	9
Osei et al. [63]	Tolbutamide-modified IVGTT	Cross-sectional	African American	32	—	0/100	NGT	White American	30	Higher insulin levels in BA but similar C-peptide levels compared to WE	9
Haffner et al. [39]	Insulin-modified IVGTT	Prospective cohort	African American	187 NGT, 101 IGT		43/57	NGT and IGT	Non-Hispanic white	229	Higher AIR in BA compared to WE when adjusted for age, sex, BMI, and WHR. Greater insulin resistance in BA by Si	9
Haffner et al. [38]	OGTT; Insulin-modified IVGTT	Prospective cohort	African American (overweight and obese)	153		45/55	T2D	Non-Hispanic white (overweight and obese)	105	OGTT: no difference in fasting and 2 h insulin. AIR higher in BA. No ethnic difference in Si. Adjusted for age, sex, obesity and WHR, fasting glucose, and therapy	9
Osei et al. [34]	OGTT	Cross-sectional	Native Ghanaian, US immigrant Ghanaian, and African American	50, 31, and 66	, , and	39/61	NGT	White American	39	Higher peak and iAUC insulin in BA compared to WE, no difference in C-peptide. Basal and postprandial HIE (by C-peptide to insulin molar ratio) lower in BA	9
Chiu et al. [64]	Hyperglycaemic clamp	Cross-sectional	African American	9	26	56/44	NGT	White American	34	Higher second-phase insulin response in BA, no difference in the 1st phase. Lower insulin sensitivity index in BA	7
Melby et al. [49]	Insulin-modified IVGTT	Cross-sectional	African American	9		0/100	NGT	White American	8	Age-matched ethnic groups. Higher AIR in BA and lower insulin sensitivity by Si in BA. Similar age, BMI, and percentage body fat between ethnicities	9
Chiu et al. [65]	Hyperglycaemic clamp	Cross-sectional	African American	11	25	45/55	NGT	White American	46	Higher 1st and 2nd phase insulin response in BA, lower insulin sensitivity index	6
Chen et al. [50]	Glucose challenge test (insulin and C-peptide 1-hour post 50 g glucose load)	Prospective cohort	African American pregnant women	343		0/100	NGT	White American pregnant women	118	Insulin and insulin to glucose ratio higher, but C-peptide and C-peptide to insulin ratio lower, in BA vs. WE. Similar BMI in both ethnic groups	8
Jensen et al. [40]	OGTT	Cohort	African American	55		38/62	NGT, IFG/IGT, and T2D	White American	217	Insulinogenic index adjusted for insulin sensitivity ((ΔI30/ΔG30)/HOMA-IR) higher in NGT BA vs. WE. No difference in IFG/IGT and T2D	7
Punyadeera et al. [26]	MMTT	Cross-sectional	Native black South African (lean and obese)	8 (lean) and 9 (obese)	(lean) and (obese)	0/100	NGT	White South African (lean and obese)	17	Higher insulin levels at 30 mins post meal in obese BA compared to obese WE. No difference in total insulin area under the curve between ethnic groups	8
Velasquez-Mieyer et al. [42]	3 h OGTT	Cross-sectional	African American (severely obese)	16		Not available by ethnicity	NGT and IGT	White American (severely obese)	26	Insulin iAUC and CIR at 30 mins higher in BA vs. WE, no significant difference in iAUC C-peptide. Similar WBISI and fat mass by DXA between ethnic groups	8
Stefan et al. [59]	OGTT, MMTT, and IVGTT	Cross-sectional	African American	30		66/33	NGT	White American	30	No ethnic difference in AUC insulin post OGTT or MMTT. Higher AIR after IVGTT in BA, when adjusted for insulin sensitivity by M-Low (from 2-step hyperinsulinaemic-euglycaemic clamp). BA and WE matched for age, sex, BMI, WHR, and percentage body fat.	9
Torrens et al. [41]	Fasting glucose and insulin to derive HOMA%B	Prospective cohort	African American	746		0/100	Nondiabetic; included subjects with IFG	Non-Hispanic white	1359	HOMA%B higher in BA after controlling for alcohol consumption, waist circumference, triglycerides, and prevalence of IFG	8
Albu et al. [43]	Insulin- or tolbutamide-modified IVGTT	Cross-sectional	African American	32		0/100	NGT and IGT	White American	28	Higher AIR in BA, which persisted when adjusted for insulin sensitivity index and measures of adiposity and skeletal muscle	7
Boule et al. [61]	IVGTT	Pre/postinterventional	African American	173	32.9 (30.8-35.0) (F); 33.1 (30.2-36.0) (M)	37/63	Nondiabetic	White American	423	AIRg and DI higher and Si lower in BA vs WE	8
Reimann et al. [28]	OGTT	Cross-sectional	Black South African (with and without abdominal obesity)	86	27 (23, 30) (without abdominal obesity); 32 (28, 35) (with abdominal obesity)	0/100	Nondiabetic	White South African (with and without abdominal obesity)	90	No ethnic difference in age, BMI, or insulin resistance by HOMA-IR. 2 h C-peptide post glucose significantly higher in BA vs. WE in the group with abdominal obesity. No ethnic difference in post glucose C-peptide in the lean group	7
Elbein et al. [44]	OGTT; Insulin- or tolbutamide-modified IVGTT	Case control	African American	159		34/66	NGT and IGT	European American	344	OGTT: area under curve insulin and insulinogenic index higher in BA. AIRg and DI higher in BA, no significant difference in Si	9
Herman et al. [35]	OGTT	RCT (data obtained before randomisation)	African American	752		26/74	IGT	White American	2117	Higher CIR in BA in the context of greater insulin resistance in BA by HOMA IR and higher BMI	7
Rasouli et al. [60]	OGTT; IVGTT; Arginine stimulation test in subgroup	Cross-sectional	African American (obese, with and without family hx of T2D)	121	38 (36-39)	41/59	NGT	White American (obese, with and without family hx of T2D)	212	No difference in 2 h OGTT insulin or insulin area under the curve, but higher AIRg in BA. No difference in AIRmax, lower DI max. BA had lower Si but higher disposition index.; No difference in age, BMI, or WHR between ethnic groups	9
Goedecke et al. [27]	OGTT; Insulin-modified IVGTT	Cross-sectional	Native black South African (lean and obese)	29	(lean) and (obese)	0/100	NGT	White South African (lean and obese)	28	Higher insulinogenic index 30 mins in BA, but no difference when adjusted for insulin sensitivity. Higher AIR and lower Si in BA, adjusted for visceral and subcut adipose volume. No ethnic difference in DI. No ethnic difference in BMI, WHR, or body fat % by DXA	9
Willig et al. [51]	Insulin- or tolbutamide-modified IVGTT	Cross-sectional	African American	87		0/100	Nondiabetic	European American	68	AIRg higher and Si lower in BA. No ethnic difference in age and BMI	8
Chandler-Laney et al. [52]	Insulin-modified IVGTT	Cross-sectional	African American	43	(premenopausal), (postmenopausal)	0/100	NGT	European American	63	Higher X0 (acute C-peptide secretion), Phi1 and Phi(tot) in BA after adjusting for age. Lower Si in BA, after adjusting for body fat % by DXA	9
Goree et al. [53]	Insulin-modified IVGTT	Cross-sectional	African American	42	Premenopausal; Postmenopausal	0/100	NGT	European American	64	AIRg and DI higher in BA. AIR remained higher after adjusting for Si.	9
Chow et al. [54]	Insulin-modified IVGTT	Cross-sectional	African American	17		0/100	Nondiabetic	White American	17	AIRg and DI higher in BA, Si lower. Matched for age and BMI. Lower WHC and higher body fat % in BA	7
Ladson et al. [55]	OGTT	Case control	African American with PCOS	36		0/100	Nondiabetic	White American with PCOS	63	Higher fasting insulin and insulinogenic index (30 mins) in BA. Similar BMI and WHR in both ethnic groups	6
Szczepaniak et al. [45]	Insulin-modified IVGTT	Cross-sectional	African American	20		35/65	NGT and IGT	Non-Hispanic white	30	Higher AIRg and DI in BA, lower Si. Ethnic groups matched for age, sex, BMI, and BP. Adjusted for HbA1c	8
Goff et al. [33]	IVGTT	Cross-sectional	UK Afro-Caribbean	35	(F); (M)	29/71	Nondiabetic	UK white	417	When adjusted for age and BMI: higher AIRg and lower Si in BA. No ethnic difference in DI	7
Ebenibo et al. [62]	IVGTT	Prospective cohort	African American	142	(), (HbA1c 5.7-6.4%)	25/75	NGT	White American	138	Within each HbA1c group, BA had higher AIRg and DI. Similar insulin sensitivity between ethnic groups by hyperinsulinaemic-euglycaemic clamp	9
Ferguson et al. [58]	HOMA%B; Insulin-modified IVGTT	Pre/postinterventional	African American	42	26 (median), 9 (IQR) (F); 27 (median), 18 (IQR) (M)	45/55	Nondiabetic	European American	106	Higher HOMA%B in BA; Lower Si and higher AIR and DI in BA, adjusted for age, sex, and BMI	8
Healy et al. [36]	HOMA%B; OGTT; Insulin-modified IVGTT	Cross-sectional	African American (obese)	84		7/93	Prediabetic (IFG and IGT)	White American (obese)	61	HOMA%B lower in BA; OGTT fasting and post glucose C-peptide levels lower in BA, no difference in insulinogenic index; Higher AIRg in BA (not significant), similar Si, and significantly higher DI in BA. BA had higher BMI and higher body fat % by DXA.	9
Goff et al. [29]	MMTT plus high-fructoseor high-glucose feeding	Cross-sectional	UK black African	9		100/0	Nondiabetic	UK white	417	No significant ethnic difference in insulin or C-peptide iAUC post feeding	7
Owei et al. [46]	IVGTT	Prospective cohort	African American (with parental T2D)	184		Not reported by ethnicity	NGT and IGT	European American (with parental T2D)	151	Higher AIR in BA. Lower insulin sensitivity by hyperinsulinaemic-euglycaemic clamp in blacks. BA younger and higher BMI	8
Shah et al. [47]	Hyperglycaemic clamp; Arginine-stimulated insulin response	Cross-sectional	African American	24	Not reported by ethnicity	Not reported by ethnicity	NGT, IGT, and T2D	White American	74	Higher acute insulin response and DI in BA, late-phase insulin tended to be higher in BA. No ethnic difference in insulin sensitivity index	8
Osei et al. [37]	Fasting parameters to determine HOMA%B; OGTT; Insulin-modified IVGTT	Cross-sectional	Overweight/obese African American	67		0/100	Prediabetic (IFG and IGT)	Overweight/obese white American	28	HOMA%B: no ethnic difference; OGTT: fasting C-peptide and peak C-peptide lower in BA, fasting and mean insulin tended to be higher; IVGTT: AIR higher in BA, not significant. DI significantly higher in BA. BA had higher BMI and higher percentage body fat by DEXA. Insulin sensitivity by Si same between ethnic groups	9
Piccinini et al. [56]	Insulin-modified IVGTT	Cross-sectional	African American	18		0/100	NGT	European American	29	Insulin secretion rate (ISR) as modelled by C-peptide higher in BA vs. WE	8
Mohandas et al. [30]	MMTT; Hyperglycaemic clamp	Cross-sectional	UK black African	19		100/0	T2D (recently diagnosed)	UK white	15	MMTT: fasting and AUC C-peptide lower in BA, no difference in insulin AUC; HC: second-phase C-peptide lower in BA, no difference in insulin iAUC. Groups matched for age, BMI, HbA1c, and duration of diabetes	9

AIR: acute insulin response; BA: black African; BMI: body mass index; CIR: corrected insulin response; DI: disposition index; DXA: dual-energy X-ray absorptiometry; FHx: family history; HIE: hepatic insulin extraction; HOMA%B: homeostatic model assessment of beta cell function; HOMA-IR: homeostatic model assessment of insulin resistance; iAUC: incremental area under the curve; IGT: impaired glucose tolerance; IVGTT: intravenous glucose tolerance test; mNOS: modified Newcastle-Ottawa scale; MMTT: mixed meal tolerance test; NGT: normal glucose tolerance; OGTT: oral glucose tolerance test (refers to 2-hour post 75 g oral glucose); PCOS: polycystic ovarian syndrome; RCT: randomised controlled trial; Si: insulin sensitivity index; T2D: type 2 diabetes; WBISI: whole-body insulin sensitivity index; WE: white European; WHR: waist-hip ratio.