IGF1 and diabetes mellitus: The attenuation of the initial association with insulin (Gunter et al, 2008) and, in another study, with glucose (Limburg et al, 2006), when other covariates were controlled for, indicates the difficulty of isolating a single primary factor from a cluster of highly correlated behavioural and metabolic variables, including body mass index, waist circumference, diabetes, physical activity, insulin, glucose, triglycerides, and IGF-1.