Table 2. Estimated hazard ratios for death from specific and all causes among twins free of baseline diabetes and coronary heart diseasea.
| Association | Hazard Ratio (95% CI) for Death | |||||
| Monozygotic and dizygotic twins (N = 903) | P Value | Monozygotic Twins (N = 440; 196 pairs, 48 unpaired twins) | P Value | Dizygotic Twins (N = 463; 208 pairs, 47 unpaired twins) | P Value | |
| Overall Association | ||||||
| Coronary Heart Disease (No. of deaths = 93∶43 monozygotic and 50 dizygotic twins) | ||||||
| Crude | 1.21 (1.07, 1.36) | .002 | 1.10 (0.94, 1.29) | .22 | 1.32 (1.11,1.58) | .002 |
| Age-adjusted | 1.19 (1.0, 1.34) | .004 | 1.10 (0.94, 1.29) | .22 | 1.28 (1.07,1.52 ) | .006 |
| Fully adjusted | 1.13 (1.01, 1.27) | .04 | 1.08 (0.93, 1.26) | .32 | 1.19 (1.003, 1.40) | .047 |
| Cardiovascular disease (No. of deaths = 172∶83 monozygotic and 89 dizygotic twins) | ||||||
| Crude | 1.15 (1.06, 1.25) | <.001 | 1.07 (0.95, 1.20 ) | .30 | 1.22 (1.10,1.36) | <.001 |
| Age-adjusted | 1.13 (1.05, 1.22) | .002 | 1.07 (0.95, 1.20 ) | .30 | 1.19 (1.07, 1.32 ) | <.001 |
| Fully adjusted | 1.09 (1.01, 1.18) | .02 | 1.03 (0.92, 1.16 ) | .59 | 1.15 (1.04, 1.27) | .005 |
| All-Cause Death (No. of deaths = 588∶272 monozygotic and 316 dizygotic twins) | ||||||
| Crude | 1.06 (1.02, 1.10) | .005 | 1.02 (0.97, 1.07) | .50 | 1.10 (1.04, 1.16) | <.001 |
| Age-adjusted | 1.04 (1.00, 1.08) | .048 | 1.007 (0.96, 1.06) | .78 | 1.07 (1.02, 1.13) | <.001 |
| Fully adjusted | 1.04 (1.00, 1.07) | .053 | 1.004 (0.96, 1.06 ) | .87 | 1.07 (1.02, 1.13 ) | .02 |
| Within-Pair Association | ||||||
| Coronary Heart Disease (No. of deaths = 93∶43 monozygotic and 50 dizygotic twins) | ||||||
| Crude | 1.09 (0.91,1.30) | .35 | 1.06 (0.79,1.43) | .70 | 1.14 (0.92,1.42) | .24 |
| Age-adjusted | 1.08 (0.91,1.29) | .36 | 1.06 (0.78,1.43) | .71 | 1.13 (0.91,1.40) | .26 |
| Fully adjusted | 1.07 (0.90, 1.28) | .43 | 1.07 (0.80,1.42) | .64 | 1.08 (0.92,1.27) | .32 |
| Test for interaction with zygosityb | .83 | |||||
| Cardiovascular disease (No. of deaths = 172∶83 monozygotic and 89 dizygotic twins) | ||||||
| Crude | 1.08 (0.96,1.22) | .21 | 1.00 (0.81,1.25) | .98 | 1.12 (0.98,1.29) | .10 |
| Age-adjusted | 1.07 (0.95,1.21) | .24 | 0.99 (0.79,1.23) | .92 | 1.12 (0.97,1.28) | .12 |
| Fully adjusted | 1. 06 (0.94, 1.19) | .33 | 0.96 (0.78,1.19) | .71 | 1.11 (0.97,1.27) | .13 |
| Test for interaction with zygosityb | .72 | |||||
| All-Cause Death (No. of deaths = 588∶272 monozygotic and 316 dizygotic twins) | ||||||
| Crude | 1.01 (0.95, 1.07) | .85 | 0.97 (0.87,1.08) | .56 | 1.03 (0.96,1.11) | .42 |
| Age-adjusted | 1.00 (0.94, 1.06) | .98 | 0.96 (0.86,1.07) | .45 | 1.03 (0.96,1.10) | .48 |
| Fully adjusted | 0.99 (0.94, 1.05) | .83 | 0.97 (0.87,1.07) | .52 | 1.01 (0.94,1.08) | .84 |
| Test for interaction with zygosityb | .80 | |||||
| Between-pair Association | ||||||
| Coronary Heart Disease (No. of deaths = 93∶43 monozygotic and 50 dizygotic twins) | ||||||
| Crude | 1.25 (1.10, 1.42) | <.001 | 1.11 (0.95,1.30) | .19 | 1.42 (1.17,1.73) | <.001 |
| Age-adjusted | 1.23 (1.09, 1.40) | .0011 | 1.11 (0.94,1.30) | .21 | 1.37 (1.13,1.65) | <.001 |
| Fully adjusted | 1.15 (1.02, 1.30) | .03 | 1.09 (0.87,1.37) | .45 | 1.24 (1.03,1.50) | .02 |
| Cardiovascular disease (No. of deaths = 172∶83 monozygotic and 89 dizygotic twins) | ||||||
| Crude | 1.18 (1.08, 1.29) | <.001 | 1.09 (0.96,1.23) | .19 | 1.28 (1.13,1.45) | <.001 |
| Age-adjusted | 1.15 (1.06, 1.26) | .0011 | 1.08 (0.95,1.22) | .22 | 1.23 (1.09,1.38) | <.001 |
| Fully adjusted | 1.10 (1.02, 1.20) | .02 | 1.04 (0.93,1.17) | .47 | 1.18 (1.05,1.32) | .004 |
| All-Cause Death (No. of deaths = 588∶272 monozygotic and 316 dizygotic twins) | ||||||
| Crude | 1.08 (1.03, 1.12) | <.001 | 1.03 (0.97,1.08) | .42 | 1.14 (1.07,1.21) | <.001 |
| Age-adjusted | 1.05 (1.01, 1.09) | .011 | 1.01 (0.96,1.07) | .60 | 1.10 (1.04,1.17) | .001 |
| Fully adjusted | 1.05 (1.01, 1.09) | .01 | 1.01 (0.96,1.06) | .71 | 1.11 (1.05,1.18) | <.001 |
Hazard ratios and 95% confidence interval were estimated for per 50 mg/dL increment in postload glucose levels at 1 hour after a 50 gram glucose load for the overall and the between-pair effects; or per 50 mg/dL difference between co-twins for the within-pair effects. Frailty survival models were used to obtain the estimates to account for clustering within a pair. Fully adjusted hazard ratios were controlled for age (continuous), smoking (never, past smokers, and current smokers), marital status (never, not married currently, and married currently), years of education (continuous), body mass index (continuous), systolic blood pressure (continuous), low-density lipoprotein cholesterol (continuous), ratio of high density lipoprotein cholesterol to triglyceride (continuous), and antihypertensives (yes/no).
Interaction between within-pair effects and zygosity was tested in the fully adjusted model.