Table 2. The construction of BAs.
| Component elements | Measurement | Statistical methods | |
|---|---|---|---|
| Telomere length (Berglund et al., 2016) | Leukocyte telomere length | qPCR | Ratio of measured telomere length to a reference length |
| DNAmAges: | Leukocyte DNA Methylation levels of: | Infinium HumanMethylation 450K BeadChip | Established clock algorithms, developed by: |
| Horvath (Horvath, 2013) | 353 age-associated CpGs | Elastic net regression (regressing CA on CpGs) | |
| Hannum (Hannum et al., 2013) | 71 age-associated CpGs | Elastic net regression (regressing CA on CpGs) | |
| PhenoAge (Levine et al., 2018) | 513 PhenoAge-associated CpGs | Step 1: Penalized proportional hazard regression (regressing time-to-death on clinical markers and CA to create PhenoAge); Step 2: Elastic net regression (regressing PhenoAge on CpGs) | |
| GrimAge (Lu et al., 2019) | Smoking pack-years- and seven plasma proteins-associated CpGs (1030 unique sites) | Step 1: Elastic net regression (regressing biomarkers on CpGs to develop DNAm-based biomarkers); Step 2: Elastic net Cox regression (regressing time-to-death on DNAm-based biomarkers and CA) | |
| Physiological age | Age-related biomarkers, including: Blood biomarkers: hemoglobin, glucose, cholesterol, Apolipoprotein B, triglyceride; Clinical markers: BMI, waist hip rate, weight, waist circumference, hip circumference, systolic BP, diastolic BP |
Blood test and physical examination | Principal component analysis and the Klemera and Doubal methods (Klemera and Doubal, 2006) |
| Cognitive function (Reynolds et al., 2005) | Verbal (crystallized) ability, spatial (fluid) ability, memory, and perceptual speed | In-person cognitive testing | Principal component analysis |
| FAI (Finkel et al., 2019) | Sensory (vision and hearing), pulmonary, strength (grip strength), and movement/balance (gait speed) | Self-reported questionnaire and physical examination | Sum of standardized scores |
| FI (Jiang et al., 2017) | 42 health deficits | Self-reported questionnaire | Ratio of the number of deficit presented to the total number of deficit considered |
BA, biological age; IPT, in-person testing; DNAmAge, DNA methylation age estimator; FAI, functional aging index; FI, frailty index; BMI, body mass index; qPCR, quantitative polymerase chain reaction; CpG, cytosine nucleotide being followed by a guanine nucleotide; BP, blood pressure.