Tension-type headache is the most prevalent primary headache type worldwide and is associated with a wide spectrum of disability. Although progress has been made in understanding the complex mechanisms that lead to the pathogenesis of tension-type headache, to date there are no clear-cut markers of what makes tension-type headache unique. Due to a relative lack of research (compared to migraine), the pathophysiology of tension-type headache is not well understood and there are gaps in the

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... iological data, particularly from Australasia. Objective: To provide a structured narrative review of the prevalence and correlates of tension-type headache, with focus on a birth cohort of young adults from the Dunedin Multidisciplinary Health and Development Study (DMHDS) in New Zealand. Method: A review of the literature was conducted to identify the epidemiological, diagnostic, methodological and pathophysiological factors that contribute to tension-type headache being a specific entity. Results: Findings suggest that prevalence rates of TTH vary across global region, age, gender and method of assessment. A wide range of risk factors for TTH was identified, and recent advances in genetic and neurobiological research have increased understanding of the etiology of TTH. Few longitudinal studies have been conducted on TTH. Conclusion: Further longitudinal epidemiological research is needed to help distinguish tension-type headache from migraine, particularly in young people. Identifying the specific markers of tension-type headache is a first step towards developing effective prevention and treatment strategies. migraine due to overlapping features [12] . Evidence suggests that features common to both types of headaches include the presence of throbbing, unilateral pain [13, 14] , muscle tension [15, 16] and aggravation by physical activity [17] . Further evidence suggests that stress, fatigue, alcohol and menstruation are common triggers for TTH and migraine [18] . TTH is the most costly type of headache for society, due to its greater prevalence [19] . As such, identifying the precursors and distinctive characteristics of TTH is a research priority. 39 Lyngberg AC, Rasmussen BK, Jorgensen T, Jensen R (2005) Prognosis of migraine and tension-type headache: A population-based followup study. Neurology 65: 580-585. 40 Sahler K (2012) Epidemiology and cultural differences in tensiontype headache. Curr Pain Headache Rep 16: 525-532. 41 Merikangas KR (2013) Contributions of epidemiology to our understanding of migraine. Headache 53: 230-246. 42 Waldie KE, McGee R, Reeder AI, Poulton R (2008) Associations between frequent headaches, persistent smoking, and attempts to quit. Headache 48: 545-552. 43 Waldie KE, Welch D (2007) Cognitive function in tension-type headache. Curr Pain Headache Rep 11: 454-460. 44 Freitag F (2013) Managing and treating tension-type headache. Med Clin North Am 97: 281-292. 45