Baseline characteristics of the 768 study participants are shown in Supplemental Tables S1 and S2
. Little difference was observed between study participants and the 93 students who were excluded because of missing data or eligibility. All participants were college students who were on average 19 years of age and there were more females (59%) than males (41%). No participants had high blood pressure (SBP > 140mmHg) and family history of heart disease (5.5%) was rare in this population. Males tended to be more overweight, to more frequently smoke non-tobacco products (Supplement Table S3
), and to have greater family history of heart disease compared to females.
Carotid intima-media thickness measurements were highly reproducible. The coefficient of variation between replicate scans (n=20) was 1.31% and the correlation coefficient was 0.97. Carotid intima-media thickness was normally distributed in this population, with a median (IQR) of 602 µm (79 µm) (Figure S1
). Males (618.0 µm; IQR 91.5 µm) had significantly higher CIMT than females (592.0 µm; IQR 74.5 µm, p-value <0.001) (Figure S2
). CIMT also differed by race/ethnicity; compared to non-Hispanic Whites (607.5 µm; IQR 79.0 µm), CIMT was higher in African Americans (631 µm; IQR 61.0 µm) and lower in Asians (587.5 µm; IQR 73.5 µm) and Hispanic Whites (588.5 µm; IQR 75.0 µm, p-value <0.0001) (Figure S3
In this group of young adults, gender and ethnic variation in other common adult cardiovascular risks factors was observed. Males had higher systolic blood pressure (SBP) and lower HDL-C and LDL-C than female participants (Supplement Table S4
). Race/ethnic differences in these characteristics were also observed ( and ). African-Americans and Hispanic Whites tended to have a larger percent of overweight and obese children and a lower level of parental education compared to non-Hispanic Whites. Mean CIMT, SBP, total cholesterol, triglycerides, HDL cholesterol and glucose also significantly differed across race/ethnicities. Levels of CRP, homocysteine, glucose and insulin were not highly correlated with one another nor with lipids (Suppl Table S5
Demographic characteristics of TROY participants by race/ethnicity
Descriptive statistics of baseline characteristics and biomarker measurements in Troy participants, by race/ethnicity (N=768)
In univariate analyses, sex, race/ethnicity, BMI, SBP, smoking non-tobacco products and homocysteine were all significantly associated with CIMT (). Current and childhood exposure to second hand smoke was not associated with CIMT. In multivariable models, sex exhibited the strongest influence on CIMT, with men having on average 15.4 µm larger CIMT compared to women (95%CI 6.6, 24.2) (). Race/ethnicity was also strongly associated with CIMT. On average, African Americans had 17.3 µm greater CIMT (95% CI −0.3, 34.8) compared to non Hispanic Whites, whereas Asians and Hispanic Whites had 14.3 (95%CI −24.3, −4.4) and 15.4 (95%CI −26.2, −4.7) µm smaller CIMT, respectively. The observed differences in CIMT by sex and race/ethnicity were not explained by underlying cardiovascular risk factors across these groups.
The effects of adult cardiovascular risk factors on IMT in college students, using univariate regression models (N=768)
Associations of cardiovascular risk factors with CIMT in college students: multivariable linear regression (N=768)
Systolic blood pressure remained a significant predictor of CIMT after adjustment for various covariates (). A 1 mmHg increase in SBP was associated with a 0.5 µm increase in CIMT (95% CI 0.0, 1.0). When categorized into quartiles, CIMT was 12.6 µm (95%CI 0.3, 24.8) higher in the highest quartile of SBP (139 ≥ SBP >113mmHg) compared to the lowest quartile (81 ≤ SBP < 101 mmHg). BMI was significantly associated with CIMT in a multivariable model (β=1.4 µm, 95% CI 0.3, 2.4). When BMI was analyzed by underweight, normal, overweight and obese sub-categories, a significant trend was also observed (p<0.02).Overweight and obese students showed increases in CIMT (β=7.7, 95% CI: −2.5, 17.8 and β=17.6, 95% CI: −1.6, 36.8) compared to normal weight participants, whereas underweight students had a lower CIMT (β=−6.9 µm, 95%CI −25.7, 12.0).
The univariate association of homocysteine with CIMT was not found with adjustment for sex or systolic blood pressure. Similarly, the increase in CIMT seen in participants who smoked non-tobacco products was no longer statistically significant after adjustment for sex, race/ethnicity or systolic blood pressure. CRP, glucose and insulin were not associated with CIMT in multivariable models. Male and female students did not have significantly different associations between known cardiovascular risk factors and IMT nor did risk factor associations with CIMT vary by race/ethnicity.
Sensitivity analyses were conducted to evaluate whether exclusion of 54 students who reported having high cholesterol or hypertension or 42 students who reported a family history of heart disease materially affected our results. The effect of SBP on CIMT was slightly reduced when individuals with a family history of heart disease were excluded (β=0.4, p=0.12) but the effects of sex, BMI and race/ethnicity on CIMT remained unaltered. Exclusion of the 176 individuals who reported ever smoking non-tobacco products did not materially alter our conclusions, although the magnitude of the effect of being African-American on IMT was strengthened.