Introduction:
These is a long-standing interest in the plausible cardiovascular benefits of soy protein and isoflavones, given the effects on several cardio-metabolic pathways (e.g., lipid profile, blood pressure, endothelial function, vascular reactivity, inflammation, insulin resistance) from pre-clinical studies and short-term intervention trials. However, the long-term prospective association between habitual soy food intake and cardiovascular mortality remains unclear. Thus, we evaluated the relation of soy protein and isoflavones intake with risk of cardiovascular mortality in middle-aged and elderly Chinese residing in Singapore.
Methods:
The Singapore Chinese Health Study is a population-based cohort that recruited 63,257 Chinese adults aged 45-74 years from 1993 to 1998. Usual diet was measured at recruitment using a validated semi-quantitative food-frequency questionnaire, and mortality information was identified via registry linkage to December 31, 2011. Cox proportional hazard models were used to calculate hazard ratios (HRs) with adjustment for potential confounders.
Results:
The median intake was 5.17 g/d for soy protein, 15.83 mg/d for soy isoflavones and 88.06 g/d for units of plain tofu-equivalent. We documented 4,780 total cardiovascular deaths during 890,473 person-years of follow-up. After adjustment for socio-demographic, lifestyle and other dietary factors, soy protein intake was not significantly associated with cardiovascular mortality: the HR (95% confidence interval) was 1.00 (reference), 1.02 (0.94-1.11), 1.02 (0.93-1.11), and 1.06 (0.97-1.17) for increasing quartiles of soy protein (P-trend=0.24). Null associations were also found for intakes of soy isoflavones (P-trend=0.83) and total tofu-equivalent (P-trend=0.79), as well as with deaths from CHD (n=2,697; P-trend=0.58) or stroke (n=1,298; P-trend=0.96). A statistically significant interaction with gender (P-interaction=0.04) was found for the relation between soy protein and cardiovascular mortality: the HRs (95% confidence intervals) across quartiles were 1.00 (reference), 1.00 (0.87-1.12), 1.05 (0.93-1.17), and 1.16 (1.03-1.31) in men (P-trend=0.02), and 1.00 (reference), 1.01 (0.88-1.16), 0.96 (0.84-1.11), and 0.95 (0.81-1.10) in women (P-trend=0.31).
Conclusions:
In this large cohort study of Chinese men and women, intake of soy foods (soy protein, isoflavones, tofu products) was not significantly associated with risk of cardiovascular mortality. However, a moderately increased risk in men cannot be excluded and requires further investigation. Overall, our results do not provide evidence for the recommendation of increasing soy food intake alone as a cardiovascular disease prevention strategy.
Dairy Food Intake Is Inversely Associated with Risk of Hypertension: The Singapore Chinese Health Study