Description of biomarkers included in the study
| Type of biomarker | Specific biomarker (method of measurement, units/lowest detection limit) | Function and clinical significance |
| Inflammatory | High-sensitivity C reactive protein (CRP) (analysed from serum using the N Latex CRP mono immunoassay on the Behring Nephelometer II analyser, with lowest detection limit of 0.2 mg/L) | CRP is an acute-phase reactant produced by the liver and is indicative of general inflammation, which may be present due to infection or chronic disease. Elevated levels are also related to psychological distress. |
| Fibrinogen (analysed from citrate plasma samples using a modification of the Clauss thrombin clotting method on the IL-ACS-TOPS analyser, with lowest detection limit of 0.5 g/L) | Fibrinogen is also produced by the liver and is involved in the blood clotting cascade. Higher levels are associated with heightened risk of cardiovascular disease. | |
| Metabolic function | Total cholesterol (measured from blood serum using enzymatic methods with a Roche Modular P analyser calibrated to the Centers for Disease Control and Prevention guidelines, mmol/L) | Total cholesterol is the overall level of cholesterol in the blood, which is transported through the bloodstream by lipoproteins: low-density lipoprotein (LDL)-cholesterol and high-density lipoprotein (HDL)-cholesterol (see below). LDL-cholesterol contributes to plaques that are deposited in the arteries, rendering them less flexible and leading to atherosclerosis and an increased risk of myocardial infarction and stroke. In addition to HDL and LDL cholesterol, triglycerides (see below) contribute to the total blood cholesterol level. |
| HDL-cholesterol (same as total cholesterol above, mmol/L) | HDL-cholesterol is involved in the delivery of LDL-cholesterol from the arteries to the liver, where it is broken down. Higher levels are therefore beneficial for the body and protective against cardiovascular disease. | |
| Triglycerides (blood samples were collected from participants who did not fast and measured from serum blood using an enzymatic method, on a Roche P module analyser, mmol/L) | Triglycerides are lipids that are used to store excess energy from the diet. Higher levels may arise as a result of obesity and other lifestyle-related risk factors, which increase the risk of cardiovascular disease. | |
| Glycated haemoglobin (HbA1c) (measured from whole blood using high-performance liquid chromatography cation exchange on a Tosoh G8 analyser, mmol/mol) | HbA1c measures glucose intolerance. HbA1c forms when high circulating levels of glucose attach themselves to the haemoglobin molecule. HbA1c levels are reflective of control of blood glucose over the previous 8–12 weeks and can be used to assist in the diagnosis of diabetes. An HbA1c level of 48 mmol/mol (6.5%) is recommended as the cut-off point for diabetes. | |
| Liver function | Gamma-glutamyl transferase (GGT) (measured with an enzymatic method on the Roche P module analyser, with lowest detection limit of 5 μ/L) | GGT is an enzyme contained in liver cells (and others such as kidney, bile duct and pancreas) and is involved in the metabolism of drugs and toxins. It is the most sensitive measure of alcohol consumption and liver damage, and elevated levels are related to cardiovascular disease. |
| Kidney function | Urea (measured from serum samples with a kinetic ultraviolet assay on a Roche P module analyser, mmol/L) | Urea is a waste product formed from the breakdown of proteins, which is excreted via urine. Elevated levels indicate that the kidneys are not functioning properly, which may be due to acute or chronic kidney disease. |
| Creatinine (measured from serum samples using an enzymatic method on the Roche P module analyser, μmol/L) | Creatinine is a chemical waste product of muscle breakdown, which is excreted by the kidneys and flows into the urine. Creatinine is therefore an indicator of how well the kidneys are cleaning the blood and is usually a more accurate measure of kidney function compared with urea. |