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As of July 31, 2012, we had followed-up the participants for an average of 9.2 years. Among the 2, 589 participants, six were lost to follow-up, giving a follow-up rate of 99.8%. Forty-five participants were excluded for missing key variables, and a total of 2, 544 people were included in the final analysis (Figure 1). During the follow-up period, a total of 120 patients with stroke were identified, with 76 ischemic and 44 hemorrhagic stroke events. The cumulative incidence rates of stroke, ischemic stroke, and hemorrhagic stroke were 4.7%, 3.0%, and 1.7%, respectively; the incidence densities were 510, 323, and 187 per 100, 000 person-years, respectively.
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Table 1 presents a comparison of baseline characteristics among the four groups. Conventional stroke risk factors such as age, sex, smoking status, drinking status, BMI, WC, SBP, DBP, hypertension, TG, HDL-C, LDL-C, and FPG, were significantly different among the four groups. Participants with a family history of CVD in either the low CRP level or the high CRP level group tended to be older, men, drinkers, and hypertensive with higher SBP and DBP measures. Participants with high CRP levels in either the family history of CVD or the no family history of CVD groups were likely to be smokers, and to have higher levels of BMI, WC, TC, TG, LDL-C, FPG, and lower levels of HDL-C.
Variables No family history of CVD/low CRP No family history of CVD/high CRP Family history of CVD/low CRP Family history of CVD/high CRP P No. of participants 1, 160 1, 054 109 221 Age, mean ± SD, y 44.98 ± 12.13 47.01 ± 11.81 48.84 ± 15.28* 50.71 ± 13.49* < 0.001 Male, n (%) 361 (31.12) 461 (43.74) 71 (65.14)* 149 (67.42)* < 0.001 Smoking, n (%) 455 (39.22) 497 (47.15)* 50 (45.87) 126 (57.01)* < 0.001 Drinking, n (%) 306 (26.38) 388 (36.81) 50 (45.87)* 105 (47.51)* < 0.001 BMI, mean ± SD, kg/m2 21.57 ± 3.03 22.92 ± 3.81* 22.15 ± 2.95 22.78 ± 3.61* < 0.001 WC, mean ± SD, cm 78.25 ± 8.43 82.82 ± 10.20* 81.07 ± 7.72 84.18 ± 9.87* < 0.001 SBP, mean ± SD, mmHg 124.77 ± 22.81 129.99 ± 23.30 141.15 ± 29.23* 148.71 ± 26.96* < 0.001 DBP, mean ± SD, mmHg 81.49 ± 12.13 85.30 ± 12.30 91.07 ± 13.86* 93.72 ± 13.09* < 0.001 HBP, n (%) 313 (26.98) 404 (38.33) 67 (61.47)* 168 (76.02)* < 0.001 TC (mmol/L) 3.44 (2.84-4.06) 3.75 (3.11-4.65)* 3.53 (2.76-4.33) 3.93 (3.20-4.74)* < 0.001 TG (mmol/L) 0.75 (0.54-1.04) 1.21 (0.86-1.84)* 0.80 (0.58-1.05) 1.22 (0.84-1.82)* < 0.001 HDL-C (mmol/L) 1.20 (1.02-1.42) 1.07 (0.91-1.30)* 1.14 (0.96-1.38) 1.09 (0.94-1.35)* < 0.001 LDL-C (mmol/L) 1.99 (1.51-2.58) 2.34 (1.69-3.15)* 2.13 (1.43-3.00) 2.41 (1.92-3.18)* < 0.001 FPG (mmol/L) 4.50 (4.10-5.10) 5.10 (4.50-5.60)* 5.00 (4.40-5.60) 5.30 (4.90-5.90)* < 0.001 Note. All values are expressed with median (inter-quartile range) unless otherwise noted. Low CRP level was defined as serum C-reactive protein concentration < 5.92 mg/L; and High CRP level was defined as serum C-reactive protein concentration ≥ 5.92 mg/L. CRP, C-reactive protein; CVD, cardiovascular disease; BMI, body mass index; WC, waist circumference; SBP, systolic blood pressure; DBP, diastolic blood pressure; HBP, diagnosis of hypertension; TC, total cholesterol; TG, triglycerides; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; FPG, fast plasma glucose; *P < 0.05 compared to group with no family history of CVD/low CRP level. Table 1. Demographic and Clinical Characteristics of 2, 544 Participants according to Four Groups
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Family history of CVD and CRP level served as independent variables in analyzing their effects on stroke. The association between a family history of CVD or CRP level and stroke is shown in Table 2. The age-sex adjusted HRs [95% confidence interval (CI)] of stroke for a family history of CVD and high CRP level were 1.76 (1.18-2.63) and 1.24 (0.81-1.90), respectively. After adjusting for age; sex; smoking and drinking status; hypertension; BMI; WC; levels of FPG, TG, LDL-C, HDL-C; and CRP level (or family history of CVD), HRs (95% CI) of stroke for family history of CVD and high CRP level were 1.24 (0.81-1.90) and 1.40 (0.94-2.09), respectively.
Variables Cases Person-years Age-sex Adjusted Multivariate Adjusted HR 95% CI P HR 95% CI P Family history of CVD* No 85 20, 527 1.00 1.00 Yes 35 2, 983 1.76 1.18-2.63 0.006 1.24 0.81-1.90 0.321 High CRP** No 46 11, 726 1.00 1.00 Yes 74 1, 784 1.44 0.99-2.07 0.055 1.40 0.94-2.09 0.103 Total*** No family history of CVD/low CRP 38 10, 732 1.00 1.00 No family history of CVD/high CRP 47 9, 795 1.23 0.80-1.89 0.344 1.25 0.79-1.98 0.335 Family history of CVD/low CRP 8 994 1.26 0.58-2.71 0.560 0.92 0.42-2.00 0.823 Family history of CVD/high CRP 27 1, 989 2.34 1.42-3.86 < 0.001 1.78 1.03-3.07 0.039 Note. HR, hazard ratio; CI, confidential interval. Low CRP was defined as serum C-reactive protein concentration < 5.92 mg/L; and High CRP level was defined as serum C-reactive protein concentration ≥ 5.92 mg/L. *Multivariate model adjusted for age, sex, smoking and drinking status, hypertension, BMI, WC and levels of blood glucose, TG, LDL-C, HDL-C and C-reactive protein. **Multivariate model adjusted for age, sex, smoking and drinking status, hypertension, family history of cardiovascular disease, BMI, WC and levels of blood glucose, TG, LDL-C and HDL-C. ***Multivariate model adjusted for age, sex, smoking and drinking status, hypertension, BMI, WC and levels of blood glucose, TG, LDL-C and HDL-C. Table 2. Adjusted HRs (95% CI) for the Stroke incidence according to Family History of CVD Status and Serum CRP Concentration
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Figure 2 shows the Kaplan-Meier curves for cumulative incidence rates of stroke for the four groups. From June 2002 to July 2012, the cumulative incidence rates of stroke in the no family history of CVD/low CRP level, no family history of CVD/high CRP level, family history of CVD/low CRP level, and family history of CVD/high CRP level groups were 3.3%, 4.5%, 7.3%, and 12.2%, respectively (log-rank P < 0.001). Participants with both a family history of CVD and high CRP levels had the highest cumulative stroke incidence rate.
Table 2 presents the age-sex adjusted and multivariate adjusted HRs (95% CI) of stroke according to family history of CVD status and CRP level. Compared with the no family history of CVD/low CRP level group, the age-sex adjusted HRs (95% CI) of stroke in the no family history of CVD/high CRP level, family history of CVD/low CRP level, and family history of CVD/high CRP level groups were 1.23 (0.80-1.89), 1.26 (0.58-2.71), and 2.34 (1.42-3.86), respectively. After further adjusting for other cardiovascular risk factors, the HR (95% CI) of stroke for the family history of CVD/high CRP level group was 1.78 (1.03-3.07), and remained significant although the HR value decreased slightly. Therefore, we set a multiplicative interaction term of family history of CVD and serum CRP in a multivariable model, but no significant interaction was detected between family history of CVD and CRP level on stroke risk (P = 0.343). In subgroup analyses stratified by age and sex, the highest stroke risk was observed in participants with both a family history of CVD and high CRP level in all subgroups, and it reached significant levels in several subgroups (Table 3). Statistical tests for interactions between the group and age or sex on stroke risk were not significant (all P > 0.05).
Subgroup No. of cases/ participants Group Pinteraction No family history of CVD/low CRP No family history of CVD/high CRP Family history of CVD/low CRP Family history of CVD/high CRP Age, years* 0.528 < 45 7/1, 208 1.00 1.40 (0.19-10.07) NA 5.99 (0.61-59.06) ≥ 45 113/1, 336 1.00 1.30 (0.81-2.09) 1.12 (0.51-2.47) 1.86 (1.05-3.29) Sex** 0.793 Men 77/1, 042 1.00 1.12 (0.63-2.00) 0.91 (0.36-2.29) 1.95 (1.01-3.78) Women 43/1, 502 1.00 1.52 (0.72-3.23) 1.43 (0.31-6.55) 2.15 (0.79-5.84) Note.NA: not available for limited sample size. The age cut-off point is 45 years (the median of age at baseline). *Multivariate model adjusted for sex, smoking and drinking status, hypertension, BMI, WC and levels of blood glucose, TG, LDL-C and HDL-C. **Multivariate model adjusted for age, smoking and drinking status, hypertension, BMI, WC and levels of blood glucose, TG, LDL-C and HDL-C. Table 3. Subgroup Analysis of Adjusted HRs (95% CI) for the stroke incidence according to Family History of CVD Status and serum CRP Concentration
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Figure 3A shows the cumulative incidence rates and multivariate adjusted HRs (95% CI) of ischemic stroke in the four groups. The cumulative incidence rates of ischemic stroke in the no family history of CVD/low CRP level, no family history of CVD/high CRP level, family history of CVD/low CRP level, and family history of CVD/high CRP level groups were 2.1%, 2.7%, 3.7%, and 9.1%, respectively (log-rank P < 0.001). Participants with a family history of CVD and high CRP levels had the highest cumulative ischemic stroke incidence rate. Compared with the no family history of CVD/low CRP level group, the multivariable adjusted HR of ischemic stroke for the family history of CVD/high CRP levels group was 2.14 (95% CI, 1.09-4.20; P = 0.027). No significant interaction was detected between a family history of CVD and CRP level on ischemic stroke risk (P = 0.091).
Figure 3. Cumulative incidence rate and multivariate adjusted HR (95% CI) of ischemic stroke (A) and hemorrhagic stroke (B) in four groups according to family history of CVD status and serum CRP concentration.
Figure 3B shows the cumulative incidence rates and multivariate adjusted HRs (95% CI) of hemorrhagic stroke in the four groups. The cumulative incidence rates of hemorrhagic stroke in the no family history of CVD/low CRP levels, no family history of CVD/high CRP levels, family history of CVD/low CRP levels, and family history of CVD/high CRP levels groups were 1.2%, 1.8%, 3.7%, and 3.2%, respectively (log-rank P = 0.052). Compared with the no family history of CVD/low CRP level group, the multivariable adjusted HRs of hemorrhagic stroke in other three groups were not statistically significant (all P > 0.05). Nor did we detect a significant interaction between a family history of CVD and CRP level on hemorrhagic stroke risk (P = 0.662).