Sample characteristics by BMI categories and hypertension status
The mean age at Wave IV was 28.9 years. Individuals in the obese BMI category were more likely to be older, female, black or Hispanic, have a lower educational attainment, no physical activity in the last week, have current or past depression, consume either larger amounts of alcohol or abstain completely, and smoke daily (). Individuals with stage II hypertension were more likely to be older black males, have a higher BMI, have a lower educational attainment, no physical activity in the past week, have current or past depression, and consume either larger amounts of alcohol or abstain completely.
Characteristics of the sample (percentages or means and standard errors)
ADHD symptoms by BMI categories and hypertension status
The percent obese was slightly higher among those in the ADHD clinically relevant categories, but this was not statistically significant (). Considering the symptoms domains separately, the proportion obese and the proportion with hypertension were greater among those with 3 or more HI or IN symptoms (). A slight, gradual increase in the prevalence of obesity and stage II hypertension was present with increasing HI and IN symptoms ().
Prevalence of overweight, obesity, and hypertension and means and standard errors for waist circumference, BMI, DBP, and SBP for clinically-relevant ADHD symptoms and categorical HI and IN symptoms
a, b. Prevalence of obesity (a) and stage II hypertension (b) by HI and IN symptom level
Mean values for Waist circumference, BMI, DBP, and SBP by ADHD symptoms
Mean waist circumference was higher among those in the ADHD clinically relevant categories compared to those with subclinical ADHD symptoms (). Mean DBP and SBP were higher, but not statistically significantly higher among those in the ADHD clinically relevant categories compared to those with subclinical ADHD symptoms. In general, means for waist circumference, BMI, DBP, and SBP increased with increasing HI and IN symptoms.
Multivariate-adjusted oddsof overweight, obesity, and hypertension
presents the odds ratio (OR) and 95% confidence intervals (CI) from the multinomial logistic and logistic regression analyses. Compared to those in the subclinical ADHD category (< 6 HI and <6 IN symptoms), those in the hyperactive-impulsive only category had the highest odds of obesity (OR, 1.63; 95% CI, 1.11-2.39). The relative odds of hypertension among those in clinically relevant categories (IN only, HI only, or Combined) were not significantly higher than among those in the subclinical ADHD category.
Adjusted odd ratio and 95% confidence intervals for multivariate multilogistic and logistic models
Compared to those with no HI or IN symptoms, those with 3 or more had the highest odds of obesity (HI 3+ OR, 1.50; 95% CI, 1.22-2.83; IN 3+ OR, 1.21; 95% CI, 1.02-1.44). In models which included the continuous variable of HI and IN (0 to 8 HI symptoms and 0 to 9 IN symptoms), one additional HI symptom was associated with a 5% increase in the odds of overweight and a 9% increase in the odds of obesity (OR overweight, 1.05; 95% CI, 1.01 – 1.09; OR obese, 1.09; 95% CI, 1.04 – 1.14). IN symptoms, when measured on a continuous scale, were not statistically significantly associated with overweight or obesity (OR overweight, 1.00; 95% CI, 0.97 – 1.04; OR obese, 1.03; 95% CI, 0.99 – 1.07) (data not shown).
Additionally, HI symptoms at the 3+ level or measured on a continuous scale were significantly associated with higher relative odds for hypertension (HI 3+ OR, 1.24; 95% CI 1.01-1.51; HI continuous OR, 1.04; 95% CI 1.00-1.09). These associations were attenuated so that no significant associations were observed when models were adjusted for BMI (HI 3+ OR, 1.16; 95% CI 0.92 - 1.45; HI continuous OR, 1.03; 95% CI 0.98 - 1.07). IN symptoms, when measured on a continuous scale, were not statistically significantly associated with hypertension regardless of whether BMI was included in the models (OR Hypertension, 1.03; 95% CI, 0.99 - 1.07; OR Hypertension adjusted for BMI 1.02; 95% CI 0.98-1.07) (data not shown).
When both the HI and IN continuous symptoms were entered together in a model, the OR were attenuated for IN symptoms, but not for HI symptoms (OR overweight for HI, 1.08; 95% CI, 1.03 – 1.13; OR overweight for IN, .96; 95% CI, .91 – 1.00 and OR obese for HI, 1.11; 95% CI, 1.06 – 1.17; OR obese for IN, .96; 95% CI, .93 – 1.01) (data not shown). There was no association between HI or IN symptoms and hypertension when both symptoms were entered into these models simultaneously.
Longitudinal associations between ADHD symptoms and BMI
The change in BMI was best described by a quadratic growth function with a homoscedastic residual structure [df = 4; X2
= 87.4, p <.001; RMSEA (90% CI) = .04 (0.04-0.05); CFI = .98; TLI = .97]. Group level means indicated that, on average, there was a significant variation in initial BMI at Wave I (α intercept
= 22.6, s.e. = .11, p < .0001), linear yearly increase in BMI (α slope
= .87, s.e. = .02, p < .0001), and a slowing of yearly increase in BMI from Wave I to Wave IV (α quadratic
= -.027, s.e. = .001, p <.0001). There was a significant positive correlation between the intercept and slope (estimate = .76, p <.0001) indicating that higher initial BMI is associated with a greater yearly increase in BMI and a significant negative correlation between intercept and quadratic (
= -.02, p < .05) indicating that higher initial BMI is associated with less downward curvature (or leveling-off) in the slope over time. The significant negative correlation between the slope and quadratic (
= -.05, p < .0001) indicated that those with greater yearly increases in BMI also showed less leveling-off over time (data not shown).
Results of the longitudinal analyses assessing the influence of ADHD symptoms on BMI growth curves, controlling for age, sex, and race can be seen in . For all models tested there were no significant model-fit statistic decrements beyond the unadjusted model. In most cases, model-fit was improved (data not shown). Models included the quadratic function, but none of the ADHD variables were related to the curvature, thus the data is not shown. There were no statistically significant associations between the clinically-relevant ADHD categories and overall BMI intercept or slope. HI symptoms assessed as either a categorical variable or on a continuous scale were associated with BMI intercept and slope. Compared to having no HI symptoms, having 3+ HI symptoms was associated with a .36 unit higher initial BMI above the age/sex/race adjusted mean intercept of 22.32 (i.e., 22.68). From Wave I to Wave IV the slope in BMI among those with 3+ HI symptoms was .12 units higher compared to those with no HI symptoms (.85 vs. the age/sex/race adjusted mean slope of .73). A similar effect was observed for the continuous 0 to 8 HI variable with higher HI symptoms associated with a higher initial BMI and steeper slope over time (γ intercept = .08, s.e. = .04, p < .05; γ slope = .02, s.e. = .01, p < .05) (data not shown).
Standardized regression coefficients, standard errors, and p-values for effect of ADHD symptoms on BMI intercept and Slope adjusted for age, sex, and race
Compared to the effect of the HI symptoms, IN symptoms had a slightly different effect on the BMI intercept and slope. IN symptoms were significantly associated with the intercept, but not the slope. Compared to having no IN symptoms, having 3+ IN symptoms was associated with a significantly higher mean BMI intercept of about half a unit (α intercept IN 3+ = 22.73 vs. α intercept IN 0 = 22.29, p < .01). Increasing IN symptoms (either assessed with the 4-categorical indicator or on the continuous 0 to 9 scale) were not associated with increasing slope in BMI over time (ps > .05). A graphic depiction of the effect of four category HI and IN symptoms on BMI intercept and slope can be viewed in .
a, b. BMI by IN (a) and HI (b) symptom level
When both IN and HI were entered in the model together, increasing IN symptoms were significantly associated with initial BMI intercept, but not slope (γ intercept = .08, s.e. =.04, p < .05 and γ slope = .00, s.e. = .01, p = .84, respectively) (data not shown). Conversely, increasing HI symptoms was not statistically associated with initial BMI intercept, but was with increasing slope in BMI (γ intercept = .02, s.e. =.05, p =.60 and γ slope = .02, s.e. = .01, p < .05, respectively) (data not shown).