Table 5.
Mediating effect of CES-D score on the total effect of dietary antioxidants (per 1 SD) on cognitive function test scores: mediation analysis relaxing the addititivity assumption and allowing for interaction between CES-D and the antioxidant exposure: HANDLS study1
| Controlled direct effect | Natural direct effect |
Natural indirect effect | Marginal total effect | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| β | (SEE) | Pwald | β | (SEE) | Pwald | β | (SEE) | Pwald | β | (SEE) | Pwald | |
| CVLT, List A | ||||||||||||
| Total carotenoids | −0.31 | (0.19) | 0.10 | −0.30 | (0.19) | 0.11 | +0.04 | (0.03) | 0.11 | −0.26 | (0.19) | 0.17 |
| Vitamin A | +0.23 | (0.36) | 0.51 | +0.22 | (0.34) | 0.52 | −0.00 | (0.07) | 0.95 | +0.22 | (0.35) | 0.53 |
| Vitamin C | −0.03 | (0.18) | 0.86 | −0.03 | (0.18) | 0.86 | +0.00 | (0.03) | 0.91 | −0.03 | (0.19) | 0.87 |
| Vitamin E | +0.63 | (0.19) | 0.001 | +0.62 | (0.19) | 0.001 | −0.07 | (0.04) | 0.040 | +0.55 | (0.19) | 0.005 |
| CVLT, DFR | ||||||||||||
| Total carotenoids | −0.09 | (0.09) | 0.30 | −0.09 | (0.09) | 0.31 | +0.02 | (0.01) | 0.12 | −0..07 | (0.09) | 0.42 |
| Vitamin A | +0.25 | (0.17) | 0.13 | +0.25 | (0.17) | 0.13 | −0.00 | (0.03) | 0.95 | +0.25 | (0.16) | 0.14 |
| Vitamin C | −0.04 | (0.09) | 0.69 | +0.04 | (0.09) | 0.69 | +0.00 | (0.01) | 0.91 | +0.04 | (0.09) | 0.68 |
| Vitamin E | +0.23 | (0.09) | 0.013 | +0.23 | (0.09) | 0.012 | −0.03 | (0.01) | 0.049 | +0.20 | (0.09) | 0.029 |
| BVRT, error count | ||||||||||||
| Total carotenoids | +0.10 | (0.15) | 0.48 | +0.10 | (0.15) | 0.51 | −0.01 | (0.01) | 0.33 | +0.08 | (0.15) | 0.56 |
| Vitamin A | −0.63 | (0.27) | 0.021 | −0.63 | (0.27) | 0.020 | +0.00 | (0.02) | 0.95 | −0.63 | (0.27) | 0.021 |
| Vitamin C | +0.02 | (0.15) | 0.84 | +0.03 | (0.15) | 0.86 | −0.00 | (0.01) | 0.91 | +0.03 | (0.15) | 0.86 |
| Vitamin E | −0.30 | (0.15) | 0.05 | −0.29 | (0.15) | 0.06 | +0.04 | (0.02) | 0.06 | −0.25 | (0.15) | 0.10 |
| Animal fluency | ||||||||||||
| Total carotenoids | +0.04 | (0.16) | 0.78 | +0.04 | (0.16) | 0.81 | +0.03 | (0.02) | 0.12 | +0.07 | (0.16) | 0.65 |
| Vitamin A | +0.44 | (0.30) | 0.13 | +0.45 | (0.30) | 0.13 | −0.00 | (0.02) | 0.95 | +0.45 | (0.30) | 0.13 |
| Vitamin C | −0.00 | (0.16) | 0.99 | −0.00 | (0.16) | 1.00 | −0.00 | (0.02) | 0.91 | +0.00 | (0.16) | 1.00 |
| Vitamin E | +0.57 | (0.16) | 0.001 | +0.57 | (0.16) | 0.001 | −0.05 | (0.03) | 0.05 | +0.52 | (0.17) | 0.002 |
| Card rotation | ||||||||||||
| Total carotenoids | −1.15 | (0.53) | 0.031 | −1.15 | (0.53) | 0.031 | +0.06 | (0.05) | 0.21 | −1.09 | (0.53) | 0.042 |
| Vitamin A | +0.94 | (0.99) | 0.34 | +0.95 | (0.99) | 0.33 | −0.00 | (0.04) | 0.95 | +0.95 | (0.99) | 0.34 |
| Vitamin C | +0.19 | (0.53) | 0.71 | +0.19 | (0.53) | 0.71 | +0.00 | (0.04) | 0.91 | +0.20 | (0.53) | 0.71 |
| Vitamin E | +1.08 | (0.55) | 0.05 | +1.07 | (0.55) | 0.05 | −0.11 | (0.07) | 0.10 | +0.96 | (0.55) | 0.08 |
Key BVRT=Benton Visual Retention Task; CDE=Controlled Direct Effect; CES-D=Center for Epidemiologic Studies-Depression; CVLT=California Verbal Learning Task; DFR=Delayed Free Recall; HANDLS=Healthy Aging in Neighborhoods of Diversity across the Life Span; MMSE=Mini-Mental State Examination; MTE=Marginal Total Effect; NDE=Natural Direct Effect; NIE=Natural Indirect Effect; OLS=Ordinary Least Square; SD=Standard Deviation; SEE=Standard Error of the Estimate; WRAT=Wide Range Achievement Test.
Multivariate OLS models adjusted for age, sex, race/ethnicity, marital status, education, WRAT total score, poverty income ratio, current smoking status, every use of illicit drugs, body mass index, and selected nutrients expressed per 1,000 kcal, namely vitamin B-6, B-12, folate, n-3 highly unsaturated fatty acids. CES-D score was entered as potential mediator alternatively for each antioxidant exposure, while others are kept in the model as covariates. Interaction between CES-D and each of the antioxidant exposure was allowed. Four parameters were estimated with SEE and p-values: CDE, NDE NIE, MTE. Those are described in more detail in statistical analysis section. For CDE, CES-D was set at a value of 11.0 (an approximation of the sample mean). Only results with significant total effects at type I error of 0.05 for at least one antioxidant are presented.