Introductions: Dairy products are rich sources of calcium. Epidemiologic evidence from Western populations suggests that intake of dairy products and calcium may reduce risk of hypertension. However, there are few reports from Asian populations which generally have lower consumption of dairy products and calcium than their Western counterparts.
Hypothesis: The association between intake of calcium and dairy products and risk of developing hypertension was evaluated in a prospective cohort study.
Methods: This study was based on the Singapore Chinese Health Study, a prospective cohort of 63,257 Chinese men and women aged 45-74 years at enrolment in 1993-1998 living in Singapore. The analysis included 37,124 participants who had no history of cancer, physician-diagnosed hypertension, and cardiovascular disease at recruitment. Diet at baseline was assessed using a validated 165-item semi-quantitative food-frequency questionnaire. The incident hypertension was defined as physician-diagnosed hypertension that the study subject reported during two follow-up interviews during 1999-2004 and 2006-2010, respectively. Cox proportional hazard regression method was used to calculate hazard ratios (HRs) and 95% confidence interval (CI) for incident hypertension associated with intake of calcium and dairy products with adjustment for potential confounders.
Results: During 354,226 person-years of follow-up, we identified 13,148 new cases of hypertension. Milk accounted for about 80% of all dairy products consumed in this population. Among all study subjects, 67% (n=24,832) hardly drank milk, 9% (n=3,236) drank at least monthly, 9% (n=3,394) drank at least weekly, and 15% (n=5,662) drank daily. Non-dairy calcium intake contributed up to 76% of total calcium intake. Compared to non-drinkers, those who drank milk daily had a statistically significant 7% lower risk of hypertension (HR 0.93; 95% CI 0.89-0.98, P-trend=0.005) after controlling for other potential lifestyle and diet risk factors and supplement usage. The intake of all dairy food was inversely associated with risk of hypertension in a dose-dependent manner: the HR (95% CI) for the second, third, and fourth quartile was 0.96 (0.92-1.02), 0.98 (0.93-1.03) and 0.93 (0.88-0.98), respectively, compared with the lowest quartile (P-trend=0.005). While total calcium intake was inversely associated with hypertension risk (HR comparing extreme quartiles 0.93; 95% CI 0.88-0.98; P-trend=0.002) there was a null association between non-dairy calcium intake and hypertension risk (HR comparing extreme quartiles 1.00; 95% CI 0.92-1.08; P-trend=0.89).
Conclusions: Consumption of milk and other dairy products may offer beneficial effect on reducing risk of hypertension in Chinese population. This beneficial effect might be independent of calcium in the dairy food.