ORIGINAL ARTICLE Calcium intake and hypertension among obese adults in United States: associations and implications explored Y Chen 1 , S Strasser 2 , Y Cao 1 , K-S Wang 1 and S Zheng 1 The relationship between calcium intake and hypertension is receiving increased research attention. The prevalence of hypertension is high among the obese populations. Calcium is a mineral that influences blood pressure. The aim of the study was to examine the association between calcium intake and hypertension in a large nationally representative sample of obese American adults. A total of 14 408 obese adults aged 20 years or older were obtained from the 1999–2010 National Health and Nutrition Examination Survey. Analysis of variance and linear regression models were used to examine relationships between calcium intake and systolic blood pressure (SBP) as well as diastolic blood pressure (DBP). Multiple logistic regression models were used to examine the association between calcium intake and hypertension after adjusting for potential confounders and interactions, including: age, race, education level, alcohol use, smoking, diabetes status, sodium intake and potassium intake. Calcium intake was significantly lower for the hypertensive group compared with the normotensive group (P o0.0001), especially among those obese female young adults aged 20–44 years and among non-diabetic obese adults. Based on ordinary linear regression analysis, a significant inverse relationship was detected, SBP and DBP decreased if calcium intake increased (SBP: regression coefficient estimate = - 0.015, P o0.0001; DBP: regression coefficient estimate = - 0.028, P o0.0001). Multiple logistic regression showed that calcium intake was negatively associated with the probability of hypertension (odds ratio (OR) = 0.81, 95% confidence interval (CI): 0.74–0.87, P o0.0001). In stratified analysis, calcium intake in youngest adults (age 20–44 years) had the lowest likelihood of hypertension (OR = 0.77, 95% CI: 0.64–0.93, P o0.0001), the inverse relationship between calcium intake and probability of hypertension was stronger among females (OR: 0.68, 95% CI: 0.55–0.84, P o0.0001), when compared with the whole sample including all of 14 408 obese adults. The protective effect of calcium intake and hypertension was found significantly in obese non-diabetic adults (OR: OR = 0.77, 95% CI: 0.67–0.89, P o0.0001) not in obese diabetic adults. SBP, DBP and calcium intake were log transformed for both ordinary linear regression analysis and logistic regression analysis. Our study findings underscore the need to explore the physiological mechanism between calcium intake and hypertension. In this study, increased calcium intake was associated with the lowest risk of hypertension. Future studies utilizing longitudinal research designs are needed to quantify therapeutic levels of calcium for control of hypertension among obese adults. Increasing calcium intake among American adults may offer promise as a cost-effective strategy to improve hypertension among obese adults; however, further scientific exploration is warranted. Journal of Human Hypertension advance online publication, 15 January 2015; doi:10.1038/jhh.2014.126 INTRODUCTION About one in three US adults—an estimated 68 million—have hypertension (defined as an elevated systolic blood pressure (SBP ⩾ 140 mm Hg), or an elevated diastolic blood pressure (DBP ⩾ 90 mm Hg). Hypertension is an expensive chronic condi- tion that increases the risk for heart disease and stroke, two of the three leading causes of death in the US. 1 Recently, epidemiologists have turned research attention to potential role calcium intake plays in hypertension control and prevention. Calcium is a main micronutrient that is critical for the development and maintenance of bone health, particularly in children and elderly adults. 2 Previous epidemiologic studies have reported an inverse relationship between calcium intake and blood pressure, typically showing that reduced intake of calcium is associated with higher blood pressure and an increased risk of developing hypertension. 3–6 However, these studies were limited by small sample sizes, variability in dietary calcium intake measurement and suboptimal blood pressure data integrity. Furthermore, few investigations have focused on the particularly high-risk group of hypertensive, which are obese adults. Obesity is an important risk factor for hypertension, and the incidence of hypertension is high in obese people. 7 Data from Framingham study showed the prevalence of hypertension in obese individuals was about twice that in that of normal weight in both gender and all age groups. 8 In a prospective cohort study by Wolf et al., nearly 1200 adults meeting criteria for overweight, obese and healthy weight controls were examined on the basis of reported health symptoms across all major biological systems, treatment/self-care practices and healthcare utilization. The research team found that there was a graded increase of reported hypertension, health problems related to all major biological systems (metabolic, cardiovascular, respiratory, skeletal and gastrointestinal), healthcare utilization and treatment, for every increase in body mass index (BMI). 9 Based on scientific findings 1 Department of Biostatistics and Epidemiology, College of Public Health, East Tennessee State University, Johnson City, TN, USA and 2 Georgia State University, School of Public Health, Atlanta, GA, USA. Correspondence: Dr S Zheng, Department of Biostatistics and Epidemiology, East Tennessee State University, 807 University Pkwy, College of Public Health, Johnson City, TN 37614, USA. E-mail: zhengs@mail.etsu.edu Received 22 April 2014; revised 18 November 2014; accepted 3 December 2014 Journal of Human Hypertension (2015), 1 – 7 © 2015 Macmillan Publishers Limited All rights reserved 0950-9240/15 www.nature.com/jhh