Protocol for <it>ADDITION-PRO</it>: a longitudinal cohort study of the cardiovascular experience of individuals at high risk for diabetes recruited from Danish primary care oleh Johansen Nanna B, Hansen Anne-Louise S, Jensen Troels M, Philipsen Annelotte, Rasmussen Signe S, Jørgensen Marit E, Simmons Rebecca K, Lauritzen Torsten, Sandbæk Annelli, Witte Daniel R