Table 2.
Description of biomarkers included in the analysis
| Biomarker | Description |
|---|---|
| Cardiovascular/Metabolic | |
| Systolic blood pressure (SBP) |
Maximum arterial blood pressure after
contraction (systole) of the heart’s left ventricle. |
| Diastolic blood pressure (DBP) |
Minimum arterial blood pressure when the heart fills with blood (diastole). |
| Total cholesterol | Waxy, fat-like substance that regulates the
permeability of cell membranes. Excess cholesterol in the blood can combine with other substances and stick to the walls of the arteries forming a plaque. Includes both LDL (bad) and HDL (good) cholesterol. |
| High-density lipoprotein (HDL) cholesterol |
Lipoprotein in the blood characterized by a
high ratio of protein relative to triglyceride and cholesterol; helps remove cholesterol from the arteries. |
| Triglycerides | Most common type of fat in the human body;
widespread in adipose tissue and typically circulate in the blood in the form of lipoproteins. |
| Glycosylated hemoglobin (HbA1c) |
Measures the level of hemoglobin A1c
(glycoprotein formed when glucose binds to hemoglobin A) in the blood; represents average blood sugar concentrations over the previous 2–3 months. |
| Body mass index (BMI) | Measure of body fat computed as the ratio of
the body weight (in kg) divided by height (in m) squared. BMI is typically classified as underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), or obese (30+), but some evidence suggests that Asians have increased health risk at a lower cutoff for obesity. |
| Waist circumference | Marker of abdominal fat content. |
| Inflammation | |
| Interleukin-6 (IL-6) | Messenger cytokine that stimulates the
synthesis of acute phase proteins (e.g., CRP, fibrinogen) in the liver as part of the inflammatory process. |
| C-reactive protein (CRP) | Protein produced in the liver that increases
markedly with acute inflammation. |
| Soluble intercellular adhesion molecule 1 (sICAM-1) and Soluble E-selectin (sE-selectin) |
Cell adhesion molecules such as ICAM-1 and
E-selectin are proteins that help cells bind to one another. Upon activation by inflammatory cytokines, ICAM-1 and E-selectin are expressed by endothelial cells that line blood vessels and facilitate the transfer of leukocytes from the blood to inflamed tissue. sICAM-1 and sE-selectin are soluble forms shed by activated cells and are measurable in blood. |
| Neuroendocrine | |
| Dehydroepiandrosterone sulfate (DHEAS) |
Steroid hormone (androgen) produced by the adrenal gland in both sexes. |
| Cortisol | Steroid hormone produced by the adrenal gland
that has anti-inflammatory and immunosuppressive properties. It is a metabolite of the primary stress hormone cortisone and serves as the main glucocorticoid in humans. Levels may be elevated in response to physical or psychological stress. |
| Epinephrine | Catecholamine secreted by the adrenal medulla
as part of the acute stress response (fight-or-flight). It is the principal hormone that causes increased blood pressure and also increases the heart rate. |
| Norepinephrine | Catecholamine produced by the adrenal medulla.
It is a precursor to epinephrine that narrows blood vessels and raises blood pressure. |
| Other markers | |
| Serum Creatinine | Breakdown product of creatine, which is an
important part of muscle. Creatinine is produced from the metabolism of protein (e.g., when muscles burn energy). Most is filtered out of the blood by the kidneys and excreted in urine. Used to evaluate kidney function. |
| Creatinine Clearance (CrCl) |
Measures the rate at which a waste
(creatinine) is cleared from the blood by the kidneys. Used to estimate the glomerular filtration rate (GFR), which reflects kidney function. Can be measured by comparing the level of creatinine in urine (based on 24h collection) with the level in the blood, but is typically estimated using a prediction equation (e.g., Cockcroft-Gault) based on serum creatinine, age, sex, and body weight. |
| Serum albumin | The main protein in human blood; helps
maintain the osmotic pressure of the blood. Low levels may be a sign of liver or kidney disease or reflect insufficient nutrition. |
| Homocysteine | Amino acid produced by the body, usually as a
byproduct of meat consumption. Linked with increased risk for cardiovascular disease; elevated levels may promote atherosclerosis. |
Note: Adapted from Table 1 in Glei et al. (Forthcoming).
Sources: American Association for Clinical Chemistry (labtestsonline.org, accessed 12 August 2013); American Heart Association (http://www.heart.org/idc/groups/heart-public/@wcm/@hcm/documents/downloadable/ucm_300308.pdf, accessed 12 August 2013); Libby & Ridker (1999); Levey et al. (2003); MedicineNet.com MedTerms dictionary (http://www.medterms.com/script/main/hp.asp, accessed 12 August 2013); MedlinePlus (http://www.nlm.nih.gov/medlineplus/mplusdictionary.html, accessed 8 August 2013); National Heart, Lung, and Blood Institute (1998); National Kidney Disease Education Program (http://nkdep.nih.gov/resources/quick-reference-uacr-gfr-508.pdf, accessed 12 August 2013); Walzog & Gaehtgens (2000); World Health Organization (http://apps.who.int/bmi/index.jsp?introPage=intro_3.html, accessed 22 January 2014).