Table 2.
Biological subsystems with component biomarker indicators and descriptive statistics.
| Biological system | Component biomarkers | Collection method | High-risk cut-pointa | |
|---|---|---|---|---|
| Sympathetic nervous systemb | 1. Epinephrine (μg/g creatine) | Urine | ≥2.47 | |
| 2. Norepinephrine (μg/g creatine) | Urine | ≥32.97 | ||
| Hypothalamic pituitary axis | 1. Cortisol (μg/g creatine) | Urine | ≥20.00 | |
| 2. DHEA-S (μg/dl) | Blood | ≤50.00 | ||
| Parasympathetic nervous systemc | 1. Root mean square of successive differences of beat-to-beat intervals (RMSSD) | Clinician assessment | ≤12.14 | |
| 2. Low frequency spectral power | Clinician assessment | ≤114.95 | ||
| 3. High frequency spectral power | Clinician assessment | ≤58.80 | ||
| Inflammation | 1. IL-6 (pg/ml) | Blood | ≥3.48 | |
| 2. Fibrinogen (mg/dl) | Blood | ≥400.00 | ||
| 3. CRP (mg/l) | Blood | ≥3.65 | ||
| 4. sE-Selectin (ng/MI) | Blood | ≥51.90 | ||
| 5. slCAM-1 (ng/MI) | Blood | ≥335.78 | ||
| Cardiovascular system | 1. Resting systolic blood pressure (mm Hg) | Clinician assessment | ≥144.00 | |
| 2. Resting heart rate (bpm) | Clinician assessment | ≥79.00 | ||
| 3. Pulse pressure (SBP - DBP) | Clinician assessment | ≥65.00 | ||
| Glucose metabolism | 1. Glycosylated hemoglobin (HbA1c) | Blood | ≥6.24 | |
| 2. Fasting glucose (mg/dl) | Blood | ≥105.00 | ||
| 3. Insulin resistance (HOMA-IR) | Blood | ≥4.36 | ||
| Lipid metabolism | 1. Body mass index (BMI) | Clinician assessment | ≥33.05 | |
| 2. Waist-to-hip ratio | Clinician assessment | ≥0.97 | ||
| 3. Triglycerides (mg/dl) | Blood | ≥156.00 | ||
| 4. HDL cholesterol (mg/dl) | Blood | ≤42.00 | ||
| 5. LDL Cholesterol (mg/dl) | Blood | ≥127.59 | ||
Abbreviations: HDL: high density lipoprotein; LDL: low density lipoprotein.
a
These values represent the cut-off for the highest quartile of scores in the MIDUS sample with the exception of the parasympathetic nervous system, DHEA, and LDL cholesterol, for which the value represents the cut-off for the lowest quartile. Participants falling beyond this value were classified as high-risk on that biomarker.
b
In a sensitivity analysis, heart rate was included as part of the sympathetic nervous system.
c
In a sensitivity analysis, RMSSD was omitted from this system to reduce redundancy.