Table 1:

Mean serum connecting peptide (C-peptide) levels of participants (n = 5902) at baseline, by characteristic

Characteristic	No.	Mean serum C-peptide level ± SD, nmol/L	p value^*
Age, yr
40–49	1817	0.73 ± 0.48	< 0.001
50–59	1185	0.73 ± 0.43
60–69	1370	0.80 ± 0.46
≥ 70	1530	0.85 ± 0.49
Sex
Male	3211	0.81 ± 0.48	< 0.001
Female	2691	0.74 ± 0.46
Ethnic background
White	3192	0.77 ± 0.45	< 0.001
Black	1335	0.74 ± 0.49
Hispanic	1185	0.85 ± 0.48
Other	190	0.74 ± 0.45
Education
Less than high school	1472	0.84 ± 0.49	< 0.001
High school	2677	0.78 ± 0.46
College or more	1753	0.72 ± 0.45
Cigarette smoking
Current smoker	1520	0.74 ± 0.48	<0.001
Former smoker	2190	0.83 ± 0.47
Never smoked	2192	0.75 ± 0.45
Alcohol use
Drinker	2985	0.73 ± 0.45	< 0.001
Nondrinker	2917	0.82 ± 0.48
Day of last meal or snack
Yesterday	3353	0.76 ± 0.43	0.02
Today	2547	0.79 ± 0.52
Hypertension
Yes	2511	0.88 ± 0.49	< 0.001
No	3391	0.70 ± 0.44
Hypercholesterolemia
Yes	2360	0.81 ± 0.46	< 0.001
No	3542	0.76 ± 0.47
Heart attack
Yes	397	0.97 ± 0.53	< 0.001
No	5505	0.76 ± 0.46
Body mass index
< 18.5	97	0.43 ± 0.34	< 0.001
18.5–24.9	2028	0.55 ± 0.36
25–29.9	2311	0.81 ± 0.42
≥ 30	1466	1.07 ± 0.50
C-reactive protein, mg/dL
< 1	5332	0.76 ± 0.45	< 0.001
≥ 1	570	0.95 ± 0.56
Total cholesterol, mmol/L
< 5.15	2093	0.75 ± 0.49	< 0.001
5.15–6.18	2206	0.77 ± 0.45
≥ 6.19	1603	0.82 ± 0.46
Triglyceride, mmol/L
< 2.26	4733	0.71 ± 0.43	< 0.001
2.26–5.65	1072	1.06 ± 0.53
> 5.65	97	1.10 ± 0.49
Serum insulin, μU/mL
< 6.38	1477	0.36 ± 0.20	< 0.001
6.38–8.92	1475	0.60 ± 0.23
8.93–12.80	1475	0.84 ± 0.28
> 12.80	1475	1.31 ± 0.47
Glycated hemoglobin, %
< 5.2	1628	0.69 ± 0.44	< 0.001
5.2–5.4	1399	0.74 ± 0.45
5.5–5.8	1418	0.77 ± 0.44
> 5.8	1457	0.93 ± 0.51
Plasma glucose, mmol/L
< 4.98	1465	0.60 ± 0.42	< 0.001
4.98–5.30	1482	0.70 ± 0.42
5.31–5.68	1482	0.80 ± 0.42
> 5.68	1473	1.00 ± 0.51

Note: SD = standard deviation.
↵* p values were calculated using t test for binomial groups and Wald F-test for categorical groups.