Table 3. Associations between cigarette smoking, alcohol consumption, and depression and percent differences (95% CI) in mitochondrial DNA copy number (log-transformed N/S ratio).
| Exposures* | Model 1a | Model 2b | Model 3c |
|---|---|---|---|
| Alcohol Consumption | |||
| Less frequent than daily use, n = 312 | Ref | Ref | Ref |
| Daily use, n = 79 | -7.9 (-20.2, 6.3) | -7.1 (-19.9, 7.8) | -6.6 (-19.6, 8.4) |
| Cigarette smoking (pack-years)–continuous | |||
| Per 5 pack-years, n = 391 | -2.6 (-5.0, -0.1) | -3.0 (-5.4, -0.5) | -2.9 (-5.4, -0.4) |
| Cigarette smoking (pack-years)–categorical | |||
| 0, n = 204 | Ref | Ref | Ref |
| > 0–4.99, n = 70 | 0.8 (-13.6, 17.7) | 3.4 (-11.7, 21.1) | 2.8 (-12.1, 20.3) |
| 5–29.99, n = 94 | 2.0 (-11.3, 17.2) | -0.0 (-13.3, 15.3) | 1.2 (-12.3, 16.8) |
| 30+, n = 23 | -27.1 (-42.9, -6.9) | -28.5 (-44.2, -8.3) | -28.5 (-44.2, -8.3) |
| Depression status | |||
| No prior history of depression, n = 303 | Ref | Ref | Ref |
| Past, but not current, depression, n = 34 | -14.4 (-30.3, 5.2) | -14.4 (-30.2, 5.1) | -15.1 (-30.8, 4.1) |
| Prevalent depression, n = 54 | 0.3 (-15.7, 19.4) | 3.5 (-13.5, 23.8) | 5.0 (-12.3, 25.8) |
* P values for per 5 smoking pack-years: 0.02; for ≥ 30 smoking pack-years: 0.009; for past, but not current depression: 0.12. All other p-values were non-significant and calculated based on Model 3. Relationships between alcohol consumption, cigarette smoking, and depression status with log-mtDNAcn were assessed for the interactions of age, sex and race/ethnicity. We did not observe any significant variations for these relationships (all p-interactions > 0.05) except for cigarette smoking. When assessing the interaction between smoking (per 5 pack-years), the p-interaction was 0.02 for sex and 0.01 for race/ethnicity.
a Model 1 was adjusted for age (years) and sex.
b Model 2 was adjusted for age (years), sex, race, education (post-college vs college or under), income (<$50,000 vs ≥ $50,000), body mass index categories (18.5–24.9, 25.0–29.9, ≥ 30 kg/m2), total physical activity (<5, 5–29.99, ≥ 30 MET-hours/week), alcohol consumption (daily vs less frequent than daily), smoking use (<30 vs ≥ 30 smoking pack-years) and depression category (past but not current history of depression or prevalent depression vs no prior history of depression)
c Model 3 was adjusted for age (years), sex, race, education (post-college vs college or under), income (<$50,000 vs ≥ $50,000), body mass index categories (18.5–24.9, 25.0–29.9, ≥ 30 kg/m2), total physical activity (<5, 5–29.99, ≥ 30 MET-hours/week), alcohol consumption (daily vs less frequent than daily), smoking use (<30 or ≥ 30 smoking pack-years) and depression category (past but not current history of depression or prevalent depression vs no prior history of depression), multivitamin use, comorbid conditions (hypertension, diabetes and use of cholesterol lowering medication).