Familial factors do not affect association between new AHA/ASA CV health index and CIMT
Association between ideal cardiovascular health and carotid intima-media thickness: a twin study
Kulshreshtha A, Goyal A, Veledar E et al.
J Am Heart Assoc. 2014 Jan 2;3(1):e000282. doi: 10.1161/JAHA.113.000282
BackgroundThe American Heart Association (AHA) and the American Stroke Association (ASA) have proposed a new public health metric: the Cardiovascular Health Index (CVHI [1,2]. The CVHI emphasises primary prevention by defining goals for risk factors that comprise the definition of “ideal” cardiovascular health. The CVHI has 7 components: 3 health factors (blood pressure, fasting glucose, and total cholesterol) and 4 health behaviours (body mass index [BMI], physical activity, healthy diet, and smoking) and classifies each of them into ideal, intermediate, and poor levels (given a score of 2, 1 or 0 respectively, yielding an overall CVHI score of 0 to 14).
Carotid Intima-Media Thickness (CIMT) is a preclinical marker for CV disease, as a quantitative index for evaluating the severity and progression of atherosclerosis. It predicts coronary heart disease and stroke, and is associated with several CV risk factors including blood pressure, dyslipidaemia, and behaviour such as smoking and physical activity [3-9].
Many health behaviours and other CVD risk factors are influenced by the familial environment, as well as by genetic factors [10,11]. Sharing of habits may confound studies of CIMT and CV risk factors [12-14].
The aim of this twin study was to assess the relationship between the CVHI and CIMT while accounting for the influence of unmeasured familial factors (early environmental and genetic). The Emory Twin Study combines data of the Twins Heart Study (THS) and the Stress and Vascular Evaluation in Twins (SAVEIT). This study had complete data on 245 twin pairs or 490 twins.
- Overall, 18% of participants had optimum (CVHI score 10-14), 77% had average (5-9) and 5% had inadequate (0-4) CV health.
- All health factors were significantly associated with CIMT categories in a mixed-model regression analysis, with a higher proportion of individuals in the poor health component category being associated with high CIMT. BMI was the only health behaviour that differed significantly between high and low CIMT categories.
- When CVHI was considered a continuous score, it was negatively correlated with CIMT (Spearman rho: -0.22, P<0.001). CIMT declined in a graded manner with an increasing number of ideal health factors and behaviours.
- Each 5-unit increase in overall CVHI score CIMT decreased by 0.045 mm (P<0.001). This association was mildly weakened after adjusting for age, college education, employment and depression.
- Analyses were done in 197 discordant twin pairs (one twin having a higher CVHI score), stratified by zygosity (76 dizygotic (DZ) discordant and 121 monozygotic (MZ) discordant). In MZ discordant twins, each 5-unit difference in CVHI score between the twins was associated with a CIMT difference of 0.05 mm (P<0.001). Among DZ twins discordant for CVHI score CIMT was not significantly associated with the CVHI score (P=0.18).
In further analyses adjusting for potential confounders, coefficients tended to be larger in MZ than in DZ pairs, but the P value for the interaction with zygosity did not reach significant (P=0.06).
ConclusionThis study shows that the newly developed CVHI is inversely associated with CIMT, which is an important preclinical predictor of clinical CV events. This association is independent of shared genetic and familial factors.
The association between CVHI and CIMT is stronger for health factors than for health behaviour, except for BMI. The association did not decrease substantially when examined within pairs, indicating that familial factors do not confound this association. Moreover, it remained strong within monozygotic twin pairs, which increases the likelihood of the association being a causal link.
This study confirms the value of determining the CVHI score, in the prevention of preclinical atherosclerosis.
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