The bottom panel of Figure 1 shows the biological measures available across waves. Height and weight have been measured across waves and used to track the obesity epidemic within this cohort. At Wave III, samples of urine and saliva were collected to test for sexually transmitted infections (STIs) and human immunodeficiency virus (HIV), and buccal cell saliva was collected from the twins and full siblings in the siblings pairs subsample for DNA extraction (see Harris et al. 2006). An expanded set of biological measures was collected at Wave IV including biomarkers of cardiovascular health (blood pressure, pulse), metabolic processes (waist circumference, HbA1c, blood glucose, lipids), immune function (EBV), inflammation (hsCRP) and a medications log. Saliva DNA, the focus of the remainder of this article, was collected from the full sample at Wave IV, including from all sibling pairs.
