Dairy Food Intake Is Inversely Associated with Risk of Hypertension: The Singapore Chinese Health Study 1,2

The Journal of Nutrition. First published ahead of print December 14, 2016 as doi: 10.3945/jn.116.238485. The Journal of Nutrition Nutritional Epidemiology Dairy Food Intake Is Inversely Associated with Risk of Hypertension: The Singapore Chinese Health Study 1,2 Mohammad Talaei, 3 *AnPan, 4 Jian-Min Yuan, 5,6 and Woon-Puay Koh 3,7 * 3 Saw Swee Hock School of Public Health, National University of Singapore, Singapore; 4 Department of Epidemiology and Biostatistics, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China; 5 Division of Cancer Control and Population Sciences, University of Pittsburgh Cancer Institute, Pittsburgh, PA; 6 Department of Epidemiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA; and 7 Duke-NUS Medical School Singapore, Singapore Abstract Background: Epidemiological evidence from Western populations suggests that dairy food intake may reduce the risk of hypertension, probably through its calcium content. However, there are no epidemiological studies among Asian populations with generally lower dairy and calcium consumption. Objective: The relation between dairy or calcium intake and risk of hypertension was evaluated in a Chinese population in Singapore. Methods: The analysis included 37,124 Chinese men and women aged 45 74 y who participated in the Singapore Chinese Health Study in 1993 1998. The subjects included in the present study had no history of cancer, hypertension, or cardiovascular disease at baseline and completed $1 follow-up interview. Diet at baseline was assessed by using a validated 165-item semiquantitative food-frequency questionnaire. The occurrence of new, physician-diagnosed hypertension was ascertained through follow-up interviews during 1999 2004 and 2006 2010. The Cox proportional hazard regression method was used to compute HRs and 95% CIs with adjustment for potential confounders. Results: Dairy food intake was inversely associated with the risk of hypertension in a dose-dependent manner: HRs across quartiles were 1.00 (lowest quartile, reference), 0.97 (95% CI: 0.92, 1.02), 0.98 (95% CI: 0.92, 1.03), and 0.93 (95% CI: 0.88, 0.98) (P-trend = 0.01). Milk accounted for ;80% of all dairy products consumed in this population. Daily milk drinkers had a lower risk of hypertension (HR: 0.94; 95% CI: 0.89, 0.99) than did nondrinkers. Nondairy calcium intake contributed 80% of total calcium intake. Although dairy calcium intake was associated with a lower risk of hypertension (HR comparing extreme quartiles: 0.88; 95% CI: 0.83, 0.94; P-trend < 0.001), there was no association for nondairy calcium intake (HR: 1.02; 95% CI: 0.94, 1.10; P-trend = 0.58). Conclusions: Baseline dairy food intake, and specifically that of milk, may reduce the risk of developing hypertension in Chinese adults, and this may not be associated with the calcium component. J Nutr doi: 10.3945/jn.116.238485. Keywords: epidemiology, hypertension, incidence, dairy products, milk, calcium, prospective studies Introduction Hypertension is a serious public health threat worldwide and is one of the leading risk factors for mortality and morbidity (1), which makes its primary prevention a public health priority. The Dietary Approaches to Stop Hypertension (DASH) eating pattern has been consistently observed to lower blood pressure independent of sodium intake and weight change (2). It was also 1 Supported by the NIH (RO1 CA144034 and UM1 CA182876). 2 Author disclosures: M Talaei, A Pan, J-M Yuan, and W-P Koh, no conflicts of interest. *To whom correspondence should be addressed. E-mail: mohammad.talaei@ u.nus.edu (M Talaei), woonpuay.koh@duke-nus.edu.sg (W-P Koh). found to reduce blood pressure to a greater extent than a diet that emphasized only fruits and vegetables (3), highlighting a potential role of other components, such as dairy foods, in the prevention of hypertension. Dairy products are rich sources of micronutrients, such as calcium, phosphorus, potassium, and vitamins, as well as essential amino acids and proteins of high biological value. It is hypothesized that these macro- and micronutrients may individually or in combination have an antihypertensive impact (4). However, the DASH diet contains 2 3 servings of low-fat dairy (3) and does not provide information about the benefit of lower doses of intake. Findings of prospective cohort studies for the association of dairy intake with hypertension risk have been inconsistent ã 2016 American Society for Nutrition. Manuscript received July 5, 2016. Initial review completed September 28, 2016. Revision accepted November 22, 2016. doi: 10.3945/jn.116.238485. Copyright (C) 2016 by the American Society for Nutrition 1of7

(5 11). Some studies found an inverse association between higher dairy intake and hypertension risk (10, 11), but others did not (5 9). Higher low-fat milk intake was associated with lower increases in blood pressure in whites but not in African Americans, suggesting that ethnic differences may modify the association between dairy intake and blood pressure (12). However, the majority of these studies were done in populations of European descent (5 11), which generally have high dairy intake and different genetic and other lifestyle factors compared with Asians. Those studies used a reference group that consisted of low-intake consumers rather than nonconsumers; thus, the findings are inevitably limited to populations with a higher range of intake (13) and may miss a potential association with dairy food intake at lower doses compared with practically no intake. Calcium has been repeatedly proposed as the reason for the potential benefits of dairy intake in reducing blood pressure and the risk of hypertension (4, 13, 14). However, its independent association was hard to assess in epidemiological studies in high dairy intake populations because dairy products are the major source of calcium in these populations; thus it is difficult, if not impossible, to eliminate a residual confounding effect of dairy food on the calcium hypertension risk association. Hence, the present analysis aimed to prospectively evaluate the association of dairy and calcium intake with the risk of developing hypertension in a Chinese population with low dairy intake as well as high intake of calcium from nondairy sources. Methods Study population. We used data from the Singapore Chinese Health Study, a population-based cohort study established between April 1993 and December 1998 on a population of 35,303 Chinese women and 27,954 Chinese men aged 45 74 y. The participants were recruited from Hokkien and Cantonese, the two major dialect groups among Chinese in Singapore. Further details of this cohort can be found in a previous publication (15). Briefly, information on demographic characteristics as well as lifestyle factors (physical activity, tobacco use, and alcohol intake), habitual diet, and medical history were collected at the time of recruitment through in-person interviews at participantsõ homes by structured questionnaires. To update the changes of lifestyle and medical conditions after baseline interviews, we conducted follow-up interviews via telephone to all surviving cohort participants in 1999 2004 (followup I) and 2006 2010 (follow-up II). All participants provided informed consent. The Singapore Chinese Health Study was approved by the Institutional Review Board at the National University of Singapore and the University of Pittsburgh. Assessment of diet, covariates, and hypertension. A semiquantitative FFQ composed of 165 commonly consumed food items in this population was administered in person by trained interviewers at recruitment to assess habitual dietary intakes of the study participants over the past 1 y. For each item, participants selected an option from 8 food-frequency categories ranging from never or hardly ever to two or more times a day and reported the related portion sizes (small, medium, or large) through provided photographs. The FFQ had been validated by repeating FFQ as well as two 24-h recalls, 1 on a weekday and 1 on a weekend, in a subset of 810 participants that yielded correlation coefficients between the 2 methods ranging from 0.51 to 0.62 for calcium intake (15). The main dairy products were listed in 6 direct items that were commonly consumed in the local Chinese population: 1) milk including powdered, whole, low fat, and chocolate but excluding as an addition to coffee or tea; 2) Milo, Ovaltine, or Horlicks (different brand names of malted milk powders); 3) probiotic cultured milk product made by fermenting a mixture of skimmed milk and lactobacillus (Yakult and Vitagen); 4) milk added to coffee or tea (evaporated or condensed); 5) butter used as bread spread; and 6) ice cream and frozen yogurt, which were considered in the computation of dairy food intake. The small amounts of dairy products used in cooking of local dishes (including rice dishes, mashed potatoes, fast foods, etc.) were also taken into account to enhance the accuracy of estimated total dairy product intake. Self-reported information was also collected about each subjectõs age, body weight, height, educational level, smoking status and physical activity at baseline. BMI was calculated by body weight in kilograms divided by height in meters squared (kg/m 2 ). The participants also selfreported their past medical conditions diagnosed by physicians, such as type 2 diabetes, coronary heart disease, and stroke. History of cancer was ascertained at the baseline interview supplemented with the record linkage analysis with nationwide Singapore Cancer Registry. At recruitment and both follow-up interviews, participants were asked if they were ever informed by a doctor that they have hypertension. In cases of positive response, age at first diagnosis was also asked. All interviews were tape-recorded and subjected to quality checks. Statistical analysis. Among 54,341 participants that were contacted in $1 follow-up interview, a total of 37,124 eligible subjects were included for this analysis (Figure 1). We used ANOVA to examine the difference in continuous variables, and the chi-square test to examine the difference in distributions between quartiles of dairy intake. Cox proportional hazard models were used to examine associations of total dairy intake, milk intake, and calcium intake at baseline with the risk of incident hypertension. Quartiles of intake were analyzed by using the lowest quartile as the reference category. Energy-adjusted values for food and nutrients by using a residual method (16) were used in statistical analysis. Person-years for each participant were calculated from the date of recruitment until the reported time of hypertension diagnosis or the date of last follow-up interview, whichever came first. In the multivariate model, we first adjusted for age (continuous), sex, interview year (1993 1995, 1996 1998), dialect group (Hokkien, Cantonese), level of FIGURE 1 Study profile. 1,600 or.3000 kcal/d for women and,700 or.3700 kcal/d for men;.3 SDs higher or lower than the mean. CVD, cardiovascular disease; HTN, hypertension. 2 of 7 Talaei et al.

education (none, primary school, secondary school, or more) in model 1 and further adjusted for physical activity level (<0.5, 0.5 3.5, $3.5 h/wk), BMI (continuous), cigarette smoking status (current, former, and never smoker), alcohol consumption (never or monthly, weekly, daily), baseline history of type 2 diabetes, and total energy intake (continuous) in model 2. In model 3, we further added dietary intakes of red meat, fish, legumes, vegetables, fruits, all grains (all in quartiles), tea, coffee, and soda and weekly use of supplemental vitamins and minerals. Model 4 included variables in addition to those in model 2: quartiles of sodium, potassium, magnesium, phosphorus, and vitamin D intake. In a sensitivity analysis, we replaced individual food and nutrient items with 2 dietary patterns that were previously identified by using a principle component analysis in this cohort: namely the vegetables-fruit-soy pattern characterized by vegetables, fruit, and soy foods, and the meat dim sum pattern rich in meat and refined starchy foods (17). Proportionality assumption was tested based on Schoenfeld residuals and no violation was seen. P values for trend were tested by including median of dairy or calcium intake in each quartile or milk intake frequency all as continuous variables in the models. The likelihood ratio test of the cross-product terms was used to test potential interactions for sex and categories of BMI (<23 and $23). All the statistical analyses were conducted by using Stata (version 11.2, Stata Corporation), with 2-sided P value < 0.05 as the threshold for statistical significance. Results The median of total dairy intake in this population was 28.2 g/d (IQR: 11.2 73.4 g/d). Milk accounted for ;80% of all dairy products consumed in this population. Among the study participants, 24,832 subjects (67%) hardly drank milk (<1 time/mo), 3236 (9%) drank $1 time/mo to 1 time/wk, 3394 (9%) drank 2 6 times/wk, and 5662 (15%) drank daily. Among milk consumers who drank $1 time/mo,93.8%reported 1 glass as their usual portion size (defined as 250 ml). Table 1 shows the distribution of participants characteristics according to total dairy intake. Dairy consumers were more likely to be women, had slightly higher levels of physical activity, smoked less, and drank alcohol less frequently. Those with higher dairy intake also had lower intake of coffee, sodas, red meat, and total grain consumption but higher intake of total fruit. Higher use of supplemental vitamins and minerals was also reported in those with higher dairy intake. During 9.5 6 4.1 y of follow-up (mean 6 SD), we documented 13,148 incident hypertension cases with an incidence rate of 37.1 (95% CI: 36.5, 37.8)/1000 person-years. We found an inverse association between higher dairy intake at baseline and risk of developing hypertension after controlling for age, sex, and sodium intake (HR for highest compared with lowest quartile: 0.91; 95% CI: 0.87, 0.96; P-trend = 0.001), and this inverse association remained statistically significant when adjusted for other potential confounders that included other dietary factors (Table 2). Those who drank milk daily had a 6% decreased risk (HR: 0.94; 95% CI: 0.89, 0.99) after adjusting for lifestyle and other dietary factors (model 3). These inverse associations did not change when we adjusted for the 2 distinct dietary patterns (the vegetable-, fruit-, and soy-rich and the dim sum and meat-rich patterns) identified in this population (data not shown). In sensitivity analyses, we performed the analysis excluding prevalent diabetes cases reported at baseline (n = 1776) and incident diabetes cases (n = 2020) reported at subsequent follow-up interviews, but the association between dairy food and risk of hypertension generally remained unchanged (data not shown). No statistically significant interaction was found between dairy intake and sex (P-interaction = 0.90) or BMI groups (P-interaction = 0.39). The median total calcium intake was 373 mg/d (IQR 304 481mg/d). Dairy calcium and nondairy calcium contributed 18.8% (IQR 8.5 35.6%) and 80.2% (IQR 62.1 91.1%) of total calcium intake, respectively. Table 3 shows that participants in the highest quartile of total calcium intake were at the lowest risk of developing hypertension (HR: 0.87; 95% CI: 0.80, 0.94) compared with the those in the lowest quartile. Almost the same finding was observed for dairy calcium (HR: 0.88; 95% CI: 0.83, 0.94). However, there was no association between nondairy calcium intake and risk of hypertension (HR: 1.00; 95% CI: 0.94, 1.07). Discussion In this large prospective cohort study, we found an inverse association between dairy intake and risk of hypertension over a decade of follow-up in Chinese middle-age and elderly people with generally low dairy intake. We also showed that a daily intake of 250 ml (one glass) of milk was associated with a decreased risk compared with no milk intake. Four-fifths of total calcium was derived from nondairy sources in this population. We found an inverse association for incident hypertension with dairy calcium but not with nondairy calcium intake. These results suggest that the beneficial effect of a dairy product may not be attributable only to its calcium content. Experimental studies have suggested several ways that dietary calcium may affect blood vessels (18). It might also affect blood pressure in relation to concomitant levels of sodium excretion (19). A cup of milk provides 275 mg Ca (;30% of daily value), according to the US Food and Drug Administration database (20). In some population-based cohort studies in the United States, an inverse association was observed between higher calcium intake and risk of hypertension (11, 21), but the results are not entirely consistent (22). On the other hand, #80% of total calcium intake is estimated to come from dairy products in the American diet (4); therefore, it is not known if the observed inverse association of dairy intake with hypertension was caused by its calcium content or other ingredients in the dairy products. In our Singapore Chinese cohort, dairy products accounted for only ;17% of total dietary calcium (23), which allows us to separately examine the association of dairy and nondairy calcium intake with the risk of hypertension. Major sources of nondairy calcium were vegetables (19%), grain products (15%), soy foods (12%), fruits (7%), and fish/shellfish (6%) in this study population (23). We found no evidence of a beneficial effect of nondairy calcium on the risk of hypertension. These results are consistent with the null results from randomized clinical trials of calcium supplementation on hypertension risk in normotensive individuals (22). Nevertheless, we cannot rule out a beneficial impact of calcium that comes from dairy products. Furthermore, most of the variation in calcium intake in our study population was due to dairy calcium, which was reflected in the much greater variation in dairy calcium compared with the variation in nondairy calcium across the quartiles of intakes. To our knowledge, it is the first longitudinal study in an Asian population regarding the link of dairy and calcium intake with the risk of hypertension. Our results concurred with a metaanalysis of 5 prospective cohort studies conducted among populations in the United States and Europe, which found a significant 13% reduction in hypertension risk comparing the highest with the lowest category of total dairy intake (14). However, the dosage substantially varied in different studies: Dairy intake and hypertension risk 3 of 7

TABLE 1 Participant characteristics according to quartiles of dairy products intake at baseline in the Singapore Chinese Health Study 1993 1998 1 Quartiles of dairy intake: median (IQR), g/d Characteristic 1: 5.51 (1.76 15.4) 2: 8.24 (1.65 17.9) 3: 35.7 (16.5 45.1) 4: 252 (125 271) n 9577 9258 9059 9230 Age, y 54.0 6 7.1 55.1 6 7.7 55.2 6 7.7 55.0 6 7.7 Female sex 3602 (37.6) 5672 (61.3) 5824 (64.3) 6169 (66.8) Menopause 2304 (64.0) 3736 (65.9) 3814 (65.5) 4060 (65.8) Dialect group Hokkien 4629 (48.3) 4122 (44.5) 4104 (45.3) 4672 (50.6) Cantonese 4948 (51.7) 5136 (55.5) 4955 (54.7) 4558 (49.4) Secondary school or higher 3064 (32.0) 2517 (27.2) 2540 (28.0) 3306 (35.8) Ever smoker 3894 (40.7) 2561 (27.7) 2352 (26.0) 1972 (21.4) Weekly or daily alcohol drinker 1945 (20.3) 1016 (11.0) 801 (8.8) 921 (10.0) Diabetes 426 (4.4) 418 (4.5) 376 (4.1) 556 (6.0) Weekly moderate activity,0.5 h/wk 7673 (80.1) 7557 (81.6) 7320 (80.8) 6675 (72.3) 0.5 3.4 h/wk 1218 (12.7) 1115 (12.0) 1131 (12.5) 1632 (17.7) $3.5 h/wk 686 (7.2) 586 (6.3) 608 (6.7) 923 (10.0) BMI, kg/m 2 22.8 6 3.1 22.9 6 3.1 22.7 6 3.1 22.5 6 3.1 Total energy intake, kcal/d 1944 6 477 1349 6 374 1314 6 462 1656 6 506 Daily tea drinker 2299 (24.0) 1825 (19.7) 1901 (21.0) 1985 (21.5) Coffee drinker Less than daily 2171 (22.7) 2478 (26.8) 2565 (28.3) 3342 (36.2) 1 cup/d 3122 (32.6) 3591 (38.8) 3182 (35.1) 3190 (34.6) $2 cup/d 4284 (44.7) 3189 (34.4) 3312 (36.6) 2698 (29.2) Sodas None 6660 (69.5) 6831 (73.8) 6784 (74.9) 7222 (78.2) #250 ml, 1 glass/wk 1485 (15.5) 1558 (16.8) 1484 (16.4) 1277 (13.8) $500 ml, 2 glasses/wk 1432 (14.9) 869 (9.4) 791 (8.7) 731 (7.9) Dairy, g/d 0 20.4 6 4.8 43.4 6 11.6 228 6 118 Red meat, g/d 32.1 6 23.2 32.0 6 15.5 31.3 6 14.8 26.4 6 17.8 Legumes, g/d 112 6 101 116 6 70.4 113 6 63.3 118 6 86.2 Fish and seafood, g/d 56.5 6 31.3 56.1 6 23.8 54.0 6 23.1 53.1 6 26.7 Total vegetables, g/d 110 6 62.9 112 6 46.3 110 6 45.6 114 6 58.6 Total fruits, g/d 187 6 179 202 6 131 199 6 127 222 6 165 Total grains, g/d 361 6 94.7 360 6 86.5 342 6 86.9 317 6 85.4 Vitamin D, IU/d 70.2 6 50.6 82.9 6 36.6 97.0 6 36.1 165 6 61.7 Total calcium, mg/d 295 6 123 349 6 102 399 6 113 619 6 193 Nondairy calcium, mg/d 284 6 103 291 6 71.3 285 6 67.5 289 6 88.7 Potassium, mg/d 1630 6 476 1730 6 335 1780 6 324 2040 6 438 Magnesium, mg/d 233 6 38.3 240 6 29.4 244 6 29.7 261 6 36.8 Sodium, mg/d 1070 6 435 1120 6 290 1130 6 279 1130 6 327 Dim sum and meat-rich pattern (4th quartile) 4125 (43.1) 1721 (18.6) 1652 (18.2) 2167 (23.5) Vegetable-, fruit-, and soy-rich pattern, 4th quartile 3205 (33.5) 1649 (17.8) 1466 (16.2) 2842 (30.8) Weekly use of vitamins and minerals 417 (4.3) 480 (5.2) 544 (6.0) 1015 (11.0) 1 Values are n (%) or mean 6 SD. All P values were,0.001 except for the proportion of menopausal women by dairy intake (P = 0.2). 691 799 g/d or 3.7 servings/d or 3.4 times/d for the highest and 156 206 g/d or 0.6 servings/d or 1.1 times/d for the lowest intake. The recently published results of Offspring Framingham Heart Study in the United States indicated a significant 8% risk reduction in hypertension with each 1-serving/wk increase in total dairy product intake, but the corresponding association for each 1-serving/wk increase in fluid milk was null (10). In a dose-response meta-analysis of 9 prospective cohort studies, Soedamah-Muthu et al. (13) estimated a significant 3% lower risk of hypertension per 200-g/d increment of total dairy intake. However, all studies were from US or European populations with high dairy intakes and were only valid within the range of 100 700 g dairy intake/d. Hence, the finding may not be directly applied to populations with relatively low consumption levels (13). In comparison, more than two-thirds of our population hardly drank milk (<1 oz/mo), and the mean intake of dairy was far below other studies among Caucasians. This makes an opportunity to investigate the potential association with the risk of hypertension at a lower range of dairy intake. Some dietary guidelines (14, 24) recommend consumption of 2 3 cups of dairy/d. Our study suggests that 1 cup milk/d may also be protective against hypertension in the Chinese population. Milk is a good dietary source for potassium, magnesium (25), phosphorus (4), and vitamin D (26), all of which have been proposed to have possible blood pressure lowering potential 4 of 7 Talaei et al.

TABLE 2 HRs (95% CIs) of incident hypertension according to intakes of dairy products and frequency of milk intake in the Singapore Chinese Health Study 1993 2010 Quartiles of total dairy intake Milk intake 1 2 3 4 P- trend 1,1 time/mo 1 time/mo to 2 6 1 time/wk times/wk Daily P- trend 1 Median intake (IQR), g/d 5.51 (1.76 15.4) 8.24 (1.65 17.9) 35.7 (16.5 45.1) 252 (125 271) Cases/person-years 3483/92,200 3338/88,580 3179/85,382 3148/88,064 8961/237,364 1084/30,379 1157/32,267 1946/54,216 Multivariate model 1 2 1.00 0.96 (0.92 1.01) 0.95 (0.90 1.00) 0.91 (0.87 0.96) 0.001 1.00 0.98 (0.92 1.04) 0.96 (0.90 1.02) 0.93 (0.89 0.98) 0.004 Multivariate model 2 3 1.00 0.97 (0.92 1.03) 0.98 (0.93 1.03) 0.92 (0.88 0.97) 0.002 1.00 0.97 (0.91 1.04) 0.95 (0.90 1.02) 0.92 (0.88 0.97) 0.001 Multivariate model 3 4 1.00 0.97 (0.92 1.02) 0.98 (0.92 1.03) 0.93 (0.88 0.98) 0.01 1.00 0.98 (0.92 1.04) 0.96 (0.90 1.02) 0.94 (0.89 0.99) 0.02 Multivariate model 4 5 1.00 0.96 (0.91 1.02) 0.95 (0.90 1.01) 0.89 (0.83 0.95) 0.001 1.00 0.96 (0.90 1.03) 0.93 (0.87 1.00) 0.89 (0.83 0.96) 0.001 1 Linear trend was tested by treating the median intake values of quartiles or frequency of intake as a continuous variable. 2 Multivariate model 1: adjusted for age, sex, dialect, year of interview, and educational level. 3 Multivariate model 2: further adjusted for BMI, physical activity, smoking status, alcohol use, baseline history of self-reported type 2 diabetes, and total energy intake. 4 Multivariate model 3: further adjusted for dietary intakes of red meat, fish, legumes, all grains, vegetables, fruits, coffee, tea, and soda and weekly use of supplemental vitamins and minerals. 5 Multivariate model 4: adjusted as for model 2 plus for dietary intakes of sodium, potassium, magnesium, phosphorus, and vitamin D. (4). In our study, the associations were persistent after adjustment for those nutrients, suggesting the independent role of dairy intake beyond those nutrients. Another mechanism in which dairy products may reduce blood pressure is through milk proteins (4). Bioactive lactotripeptides are hypothesized to lower blood pressure by inhibition of angiotensin-converting enzyme and opioid-like activities (4, 27). A reciprocal relation between dairy intake and healthier dietary pattern has been shown in our study as well as in other studies (6, 7, 10) and suggests that the association between dairy intake and risk of hypertension could be confounded by generally healthier lifestyle and eating habits. Although it was not considered in some studies (8, 9), we adjusted for several potential confounders, including dietary pattern, and did not find considerable changes in the risk estimates. Nevertheless, residual confounding could not be entirely ruled out in observational studies. Of note, sodium intake was comparable among the quartiles of diary intake. Hence, sodium did not significantly confound the dairy-hypertension association. However, this should be interpreted with caution because dietary assessment TABLE 3 HRs (95% CIs) of incident hypertension according to intakes of total, dairy, and nondairy calcium in the Singapore Chinese Health Study 1993 2010 Quartiles of calcium intake 1 2 3 4 P-trend 1 Total calcium Median intake (IQR), mg/d 266 (198 353) 281 (219 360) 384 (313 472) 640 (532 795) Cases/person-years 3366/91,295 3362/86,972 3260/87,581 3137/87,787 Multivariate model 1 2 1.00 1.03 (0.98 1.09) 1.00 (0.95 1.05) 0.95 (0.90 1.00) 0.007 Multivariate model 2 3 1.00 1.03 (0.98 1.08) 0.99 (0.94 1.04) 0.94 (0.89 0.99) 0.001 Multivariate model 3 4 1.00 1.02 (0.97 1.07) 0.98 (0.92 1.03) 0.93 (0.88 0.99) 0.006 Multivariate model 4 5 1.00 0.99 (0.93 1.04) 0.93 (0.88 0.99) 0.87 (0.80 0.94), 0.001 Dairy calcium Median intake (IQR), mg/d 7.36 (2.38 24.3) 26.9 (4.93 49.2) 105 (69.2 117) 311 (221 374) Cases/person-years 3466/91,639 3303/86,702 3270/88,579 3109/87,306 Multivariate model 1 2 1.00 0.98 (0.94 1.03) 0.95 (0.91 1.00) 0.91 (0.87 0.96), 0.001 Multivariate model 2 3 1.00 0.99 (0.94 1.04) 0.96 (0.92 1.01) 0.92 (0.87 0.96), 0.001 Multivariate model 3 4 1.00 0.99 (0.94 1.04) 0.97 (0.92 1.02) 0.93 (0.88 0.98) 0.003 Multivariate model 4 5 1.00 0.98 (0.93 1.03) 0.95 (0.90 1.00) 0.88 (0.83 0.94), 0.001 Nondairy calcium Median intake (IQR), mg/d 216 (164 280) 220 (174 278) 270 (220 328) 392 (320 488) Cases/person-years 3312/90,010 3182/87,458 3323/88,243 3331/88,515 Multivariate model 1 2 1.00 0.98 (0.94 1.03) 1.03 (0.98 1.08) 1.04 (0.99 1.10) 0.04 Multivariate model 2 3 1.00 0.99 (0.94 1.04) 1.01 (0.96 1.07) 1.01 (0.96 1.06) 0.62 Multivariate model 3 4 1.00 0.98 (0.93 1.04) 1.01 (0.95 1.08) 1.02 (0.94 1.10) 0.58 Multivariate model 4 5 1.00 0.97 (0.92 1.02) 0.99 (0.93 1.05) 1.00 (0.94 1.06) 0.78 1 Linear trend was tested by treating the median intake values of quartiles as a continuous variable. 2 Multivariate model 1: adjusted for age, sex, dialect, year of interview, and educational level. 3 Multivariate model 2: further adjusted for BMI, physical activity, smoking status, alcohol use, baseline history of self-reported type 2 diabetes, and total energy intake. 4 Multivariate model 3: further adjusted for dietary intakes of red meat, fish, legumes, all grains, vegetables, fruits, coffee, tea, and soda and weekly use of supplemental vitamins and minerals. 5 Multivariate model 4: adjusted as for model 2 plus for dietary intakes of sodium, potassium, magnesium, phosphorus, and vitamin D. Dairy intake and hypertension risk 5 of 7

tools, such as FFQs, often underestimate sodium intake because of underreporting and inherent difficulties in capturing information about recipes and discretionary salt (28). Milk consumption may also serve as a replacement for a sweetened beverage, which was shown to be adversely associated with hypertension risk (13, 29). Epidemiological evidence has shown that light-to-moderate coffee consumption may elevate hypertension risk (30), whereas drinking green tea may have a favorable effect on blood pressure (31). We also showed that the inverse association between milk and hypertension was not confounded by intake of these other beverages in this population. Our study is subject to some limitations. First, self-reported dietary intake could result in measurement error, but this was most likely nondifferential misclassification leading to underestimation of the risk reduction in cohort studies. With regard to other covariates, the self-reported data may have also resulted in some misclassification and residual confounding. A potential confounding effect may have also occurred because of the link between socially related dietary patterns and medical access, although we have tried to overcome this by adjusting for the highest educational level as a surrogate for socioeconomic factor and medical access. Second, diet was assessed only at baseline, and information on potential changes in exposure levels during follow-up was not available. This assumption that dietary intake remained fairly stable may lead to subsequent nondifferential misclassification that could result in an underestimation of the real risk estimate. This also raises questions about the potential lifelong-lasting effect of dairy intake in protecting against hypertension. Third, hypertension status was also self-reported, and misclassification was possible, although most likely nondifferential. However, in a home visit for a biospecimen collection conducted among a subgroup of 12,646 participants who had reported physician-diagnosed hypertension, 88% of them reported to take antihypertensive medications, and this indicates a reasonable validity of self-reported diagnosis. Fourth, we did not gather information about the fat content of dairy products and were not able to distinguish between high- and low-fat dairy; however, during the period of recruitment, low-fat dairy was less common in the population, and we speculated that most dairy products were full fat. Furthermore, milk was the major source of dairy intake, and our results may not be generalizable to other populations with substantial varieties of dairy products, such as cheese, butter, yogurt, cream, etc. In conclusion, we found that low-to-moderate dairy intake, such as drinking 250 ml (1 glass) of milk daily, may reduce hypertension risk in the Chinese population, and our findings suggest that this beneficial effect may not be attributable to its calcium contents because calcium from other sources showed no significant association. Further studies in Asian populations are needed to confirm our findings, particularly in the contemporary cohorts with more varieties of dairy products and increased consumption levels. Acknowledgments We thank Siew-Hong Low of the National University of Singapore for supervising the fieldwork in the Singapore Chinese Health Study and Renwei Wang for the maintenance of the cohort study database. Finally, we thank the founding Principal Investigator of the Singapore Chinese Health Study, Mimi C Yu. W-PK designed and conducted the research and had primary responsibility for the final content; MT and W-PK performed the statistical analysis; MT interpreted the data and wrote the manuscript; and AP, J-MY, and W-PK assisted in interpreting the data and critically revised the first draft. All authors read and approved the final manuscript. References 1. GBD 2013 Risk Factors Collaborators; Forouzanfar MH, Alexander L, Anderson HR, Bachman VF, Biryukov S, Brauer M, Burnett R, Casey D, Coates MM, et al. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 188 countries, 1990 2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2015;386:2287 323. 2. Saneei P, Salehi-Abargouei A, Esmaillzadeh A, Azadbakht L. Influence of Dietary Approaches to Stop Hypertension (DASH) diet on blood pressure: a systematic review and meta-analysis on randomized controlled trials. Nutr Metab Cardiovasc Dis 2014;24:1253 61. 3. Appel LJ, Brands MW, Daniels SR, Karanja N, Elmer PJ, Sacks FM; American Heart Association. Dietary approaches to prevent and treat hypertension: a scientific statement from the American Heart Association. Hypertension 2006;47:296 308. 4. McGrane MM, Essery E, Obbagy J, Lyon J, Macneil P, Spahn J, Van Horn L. Dairy consumption, blood pressure, and risk of hypertension: an evidence-based review of recent literature. Curr Cardiovasc Risk Rep 2011;5:287 98. 5. Alonso A, Beunza JJ, Delgado-Rodriguez M, Martinez JA, Martinez- Gonzalez MA. Low-fat dairy consumption and reduced risk of hypertension: the Seguimiento Universidad de Navarra (SUN) cohort. Am J Clin Nutr 2005;82:972 9. 6. Engberink MF, Geleijnse JM, de Jong N, Smit HA, Kok FJ, Verschuren WM. Dairy intake, blood pressure, and incident hypertension in a general Dutch population. J Nutr 2009;139:582 7. 7. Engberink MF, Hendriksen MA, Schouten EG, van Rooij FJ, Hofman A, Witteman JC, Geleijnse JM. Inverse association between dairy intake and hypertension: the Rotterdam Study. Am J Clin Nutr 2009;89:1877 83. 8. Heraclides A, Mishra GD, Hardy RJ, Geleijnse JM, Black S, Prynne CJ, Kuh D, Soedamah-Muthu SS. Dairy intake, blood pressure and incident hypertension in a general British population: the 1946 birth cohort. Eur J Nutr 2012;51:583 91. 9. Steffen LM, Kroenke CH, Yu X, Pereira MA, Slattery ML, Van Horn L, Gross MD, Jacobs DR Jr. Associations of plant food, dairy product, and meat intakes with 15-y incidence of elevated blood pressure in young black and white adults: the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Am J Clin Nutr 2005;82:1169 77, quiz 363 4. 10. Wang H, Fox CS, Troy LM, McKeown NM, Jacques PF. Longitudinal association of dairy consumption with the changes in blood pressure and the risk of incident hypertension: the Framingham Heart Study. Br J Nutr 2015;114:1887 99. 11. Wang L, Manson JE, Buring JE, Lee IM, Sesso HD. Dietary intake of dairy products, calcium, and vitamin D and the risk of hypertension in middle-aged and older women. Hypertension 2008;51:1073 9. 12. Alonso A, Steffen LM, Folsom AR. Dairy intake and changes in blood pressure over 9 years: the ARIC study. Eur J Clin Nutr 2009;63:1272 5. 13. Soedamah-Muthu SS, Verberne LD, Ding EL, Engberink MF, Geleijnse JM. Dairy consumption and incidence of hypertension: a doseresponse meta-analysis of prospective cohort studies. Hypertension 2012;60:1131 7. 14. Ralston RA, Lee JH, Truby H, Palermo CE, Walker KZ. A systematic review and meta-analysis of elevated blood pressure and consumption of dairy foods. J Hum Hypertens 2012;26:3 13. 15. Hankin JH, Stram DO, Arakawa K, Park S, Low SH, Lee HP, Yu MC. Singapore Chinese Health Study: development, validation, and calibration of the quantitative food frequency questionnaire. Nutr Cancer 2001;39:187 95. 16. Willett W, Stampfer MJ. Implications of total energy intake for epidemiologic analysis. In: Willett W, editor. Nutritional epidemiology. 3rd ed. Oxford (United Kingdom): Oxford University Press; 2013. p. 260. 17. Butler LM, Wu AH, Wang R, Koh WP, Yuan JM, Yu MC. A vegetablefruit-soy dietary pattern protects against breast cancer among postmenopausal Singapore Chinese women. Am J Clin Nutr 2010;91:1013 9. 18. Houston MC, Harper KJ. Potassium, magnesium, and calcium: their role in both the cause and treatment of hypertension. J Clin Hypertens (Greenwich) 2008;10:3 11. 19. Resnick LM, Oparil S, Chait A, Haynes RB, Kris-Etherton P, Stern JS, Clark S, Holcomb S, Hatton DC, Metz JA, et al. Factors affecting blood pressure responses to diet: the Vanguard study. Am J Hypertens 2000;13:956 65. 6 of 7 Talaei et al.

20. US Department of Agriculture; Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28 [Internet]. [cited 2016 Oct 10]. Available from: https://ndb.nal.usda.gov/ ndb/. 21. Ascherio A, Rimm EB, Giovannucci EL, Colditz GA, Rosner B, Willett WC, Sacks F, Stampfer MJ. A prospective study of nutritional factors and hypertension among US men. Circulation 1992;86:1475 84. 22. Chung M, Balk EM, Brendel M, Ip S, Lau J, Lee J, Lichtenstein A, Patel K, Raman G, Tatsioni A, et al. Vitamin D and calcium: a systematic review of health outcomes. Evid Rep Technol Assess (Full Rep) 2009;183:1 420. 23. Butler LM, Wong AS, Koh WP, Wang R, Yuan JM, Yu MC. Calcium intake increases risk of prostate cancer among Singapore Chinese. Cancer Res 2010;70:4941 8. 24. US Department of Health and Human Services; US Department of Agriculture. 2015 2020 Dietary Guidelines for Americans: a closer look inside healthy eating patterns [Internet]. [cited 2016 Jan 19]. Available from: http://health.gov/dietaryguidelines/2015/guidelines/chapter-1/ a-closer-look-inside-healthy-eating-patterns/. 25. Frisoli TM, Schmieder RE, Grodzicki T, Messerli FH. Beyond salt: lifestyle modifications and blood pressure. Eur Heart J 2011;32:3081 7. 26. Kunutsor SK, Burgess S, Munroe PB, Khan H. Vitamin D and high blood pressure: causal association or epiphenomenon? Eur J Epidemiol 2014;29:1 14. 27. Fekete ÁA, Givens DI, Lovegrove JA. The impact of milk proteins and peptides on blood pressure and vascular function: a review of evidence from human intervention studies. Nutr Res Rev 2013;26:177 90. 28. McLean RM. Measuring population sodium intake: a review of methods. Nutrients 2014;6:4651 62. 29. Cohen L, Curhan G, Forman J. Association of sweetened beverage intake with incident hypertension. J Gen Intern Med 2012;27:1127 34. 30. Zhang Z, Hu G, Caballero B, Appel L, Chen L. Habitual coffee consumption and risk of hypertension: a systematic review and metaanalysis of prospective observational studies. Am J Clin Nutr 2011;93:1212 9. 31. Yang YC, Lu FH, Wu JS, Wu CH, Chang CJ. The protective effect of habitual tea consumption on hypertension. Arch Intern Med 2004;164:1534 40. Dairy intake and hypertension risk 7 of 7