Risk factors for aneurysmal subarachnoid hemorrhage – BMI and serum lipids: 11-year follow-up of the HUNT and the Tromsø Study in Norway Introduction Although a familial preponderance suggests a genetic component, it is likely that most cases of aneurysmal subarachnoid hemorrhage (aSAH) can be attributed to life-style factors (1). Because of the low incidence of SAH, it has been difficult to identify risk factors in prospective studies. None- theless, female sex, smoking, hypertension, and excessive alcohol intake are now regarded as established risk factors, whereas the role of body mass index (BMI) and serum lipids remains uncertain (2). In a previous report from the first Nord-Trøndelag Health Study (HUNT 1), we found reduced risk in overweight people (BMI 25–29.9) (3), and others have either reported negative (4–7) or no association of BMI with the risk of SAH (8–10). Similarly, conflicting results have been reported for total cholesterol, some showing a negative association (6, 7, 11–13), whereas others have reported no association with SAH risk (5, 8, 9, 14). Because of these conflicting results, we wanted to assess the associations of BMI and serum lipids Acta Neurol Scand 2012: 125: 382–388 DOI: 10.1111/j.1600-0404.2011.01578.x Ó 2011 John Wiley & Sons A ⁄ S ACTA NEUROLOGICA SCANDINAVICA Sandvei MS, Lindekleiv H, Romundstad PR, Mu¨ller TB, Vatten LJ, Ingebrigtsen T, Njølstad I, Mathiesen EB, Vik A. Risk factors for aneurysmal subarachnoid hemorrhage – BMI and serum lipids: 11-year follow-up of the HUNT and the Tromsø Study in Norway. Acta Neurol Scand: 2012: 125: 382–388. Ó 2011 John Wiley & Sons A ⁄ S. Objectives – Life-style factors have been associated with the risk for aneurysmal subarachnoid hemorrhage (aSAH), but it is not clear whether body mass index (BMI) and serum lipids are associated with risk. We prospectively assessed these associations in two large population studies. Methods – A total of 65,526 participants in the Nord-Trøndelag Health Study (1995–1997) and 26,882 participants in the Tromsø Study (1994–1995) were included. Studies included measurements of body weight and height, serum lipids, and self- administered questionnaires. Participants who experienced aSAH were identified, and hazard ratios (HRs) were estimated using Cox regression analysis. Results – During 11 years of follow-up, aSAH was diagnosed in 122 participants. Overweight (BMI 25–29.9) was negatively associated with the risk of aSAH (HR 0.7, 95% CI 0.4–1.0). There was no over all association of total serum cholesterol, HDL cholesterol, or triglycerides with the risk of aSAH, but in participants younger than 50 years, HDL cholesterol was inversely associated with the risk (HR per standard deviation increase 0.6, 95% CI 0.4–0.9). Conclusions – Overweight may be associated with reduced risk of aSAH, but there was no over all association of total serum cholesterol, HDL cholesterol, or triglycerides with the risk of aSAH in this prospective study. M. S. Sandvei 1 , H. Lindekleiv 2,3 , P. R. Romundstad 4 , T. B. Müller 5 , L. J. Vatten 4 , T. Ingebrigtsen 2,6 , I. Njølstad 7 , E. B. Mathiesen 2,8* , A. Vik 1,5* 1 Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway; 2 Department of Clinical Medicine, Faculty of Health Sciences, University of Tromsø, Tromsø, Norway; 3 Department of Radiology, University Hospital of North Norway, Tromsø, Norway; 4 Department of Public Health and Community Medicine, Norwegian University of Science and Technology, Trondheim, Norway; 5 Department of Neurosurgery, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway; 6 Department of Neurosurgery, University Hospital of North Norway, Tromsø, Norway; 7 Department of Community Medicine, Faculty of Health Sciences, University of Tromsø, Norway; 8 Department of Neurology and Clinical Neurophysiology, University Hospital of North Norway, Tromsø, Norway Key words: aneurysm; cholesterol; epidemiology; risk factors; subarachnoid hemorrhage M. S. Sandvei, NTNU Det medisinske fakultet, Institutt for nevromedisin, Postboks 8905, Medisinsk teknisk forskningssenter, 7491 Trondheim, Norway Tel.: +47 414 698 25 Fax: +47 73 598 795 e-mail: marie.s.sandvei@ntnu.no *Authors who contributed equally to this work Accepted for publication June 29, 2011 382