Our analysis of a large cohort of young adult Chinese women revealed that both early and late age at menarche are associated with the risk of hypertension. Among lifestyles known to be risk factors for hypertension, BMI showed interaction with age at menarche. To the best of our knowledge, our study is the first to demonstrate that the risk of hypertension in a vulnerable population, that is young adult women with menarche age of ≤12 or ≥ 16, is substantially increased among women with other key risk factors (higher BMI, psychological stress, passive smoking and an imbalanced diet). This finding suggests that the risk of hypertension in this population could be mitigated through lifestyle modification, and thereby provides huge public health, societal and economic benefit.High blood pressure increases the risk of many other conditions, including heart disease, heart attacks, strokes, heart failure, kidney disease and vascular dementia. Risk factors for hypertension include age, being overweight or obese, dietary habits (e.g. high consumption of salt, alcohol or coffee and lower intake of vegetables), sedentary lifestyle, and insufficient sleep. In this study, passive smoking was associated with prevalence of hypertension in young adult women, but not with active smoking. For cultural reasons, active smoking may have been underreported in this cohort of young Chinese women, which may therefore serve to explain the apparent absence of an association with hypertension in our study . The risk of hypertension is therefore modifiable by adopting healthy lifestyles, although there are also inherited risk factors, including sex, ethnicity and family history of the disease. It is not yet clear whether those individuals inheriting such risk factors could substantially benefit in reducing their risk of hypertension through lifestyle changes.Early age at menarche has been shown to be associated with increased risk of hypertension in middle-aged and elderly Western women, and an association between late age at menarche and hypertension or other cardiovascular disease was recently reported in a large UK cohort [7, 18]. In this ELEFANT study, we similarly observed that young Chinese women with either early or late menarche age are at increased risk of developing hypertension. The pathophysiology underlying this association has not been elucidated, but may be related to obesity later in life. Early age at menarche is associated with increased adiposity in adulthood independent of childhood BMI, and especially with increased BMI in adult women below the age of 40 . Our study examined the risk of hypertension among women under 40 and revealed this to be particularly high among obese women with early menarche, thereby identifying a population who could benefit from intervention strategies to reduce CVD incidence. In contrast, as later age at menarche is associated with lower BMI later in life , its association with hypertension may be through alternative mechanisms. One such possibility is through reduced exposure to oestrogen, which can reduce blood pressure through stimulation of endothelial nitric oxide synthase , although there is conflicting evidence for the effect of oestrogen upon blood pressure .Young adults with even mildly higher blood pressure display increased incidence of heart disease in later life . However, known as a “silent killer”, undiagnosed hypertension is common especially in young adults . Within our cohort, 90% of participants meeting the criteria for hypertension diagnosis had not been previously diagnosed (Additional file 6). Our study has revealed that early and late menarche age are associated with the development of hypertension in young adults. This finding has important implications, as the early detection of hypertension and maintenance of healthy blood pressure in young women with earlier and later menarche age could be critical to decrease the incidence CVD in later life.Modification of lifestyle has been shown to impact upon lowering blood pressure and has been proposed as a non-pharmacological approach to the prevention and treatment of hypertension . Many studies have focused on modification of a single lifestyle factor for prevention [26, 27], though results of multiple interventions, including dietary intervention with increased physical activity, have been demonstrated to be effective in reducing blood pressure in middle-aged (mean age: 50) men and women [28, 29]. We report that risk of hypertension in vulnerable young adult women, those with either early or late menarche age, increases with the additive associations of multiple high-risk lifestyles. The recommendation of healthy lifestyles to those vulnerable individuals when young could be a highly potent and cost-effective means to reduce the incidence of hypertension and CVD in later life.Our study utilised a large and well-characterised cohort, with complete information on socio-economic status, lifestyles and reproductive characteristics. All clinical and other questionnaire data measures were carefully standardised and assessed. We rigorously controlled for potential confounders to analyse the relative risk of hypertension. Further, the examination of hypertension in young adult women enabled the elucidation of the associations of menarche age on risk without potential confounding through post-menopausal effects.Our study contains several potential limitations. The age at menarche was recalled at the time of enrolment, when the participants were young adults. However, it has been shown that the self-reported age at menarche is highly correlated with original age at menarche . Secondly, childhood adiposity, which is considered a risk factor for early pubertal timing , was not available in this study. Thirdly, physical activity is potentially suitable as a further modifiable lifestyle factor for investigation in relation to modulation of hypertension risk, but such data was not available within the Young ELEFANT study. Finally, the collected dietary data does not include specific analysis of sodium intake, which is associated with the risk of hypertension. In addition, the classification of obesity by BMI score differs between Asian and Western populations, therefore our findings will need to be validated in a Western cohort. Finally, on account of the observational characteristic of cross-sectional studies, residual confounding by unknown factors might exist.