Food Omega-3 Fatty Acid Intake of Individuals (Total, Linolenic Acid, Long-Chain) and Their Blood Pressure. INTERMAP Study

Findings from short-term randomized trials indicate that dietary supplements of omega-3 polyunsaturated fatty acids (PFA) lower blood pressure of hypertensive persons, but effect size in nonhypertensive individuals is small and nonsignificant. Data are lacking on food omega-3 PFA and blood pressure in general populations. The International Study of Macro- and Micro-nutrients and Blood Pressure (INTERMAP) is an international cross-sectional epidemiologic study of 4680 men and women ages 40 to 59 from 17 population-based samples in China, Japan, United Kingdom, and United States. We report associations of food omega-3 PFA intake (total, linolenic acid, long-chain) of individuals with blood pressure. Systolic and diastolic blood pressure were measured 8 times at 4 visits. With several models to control for possible confounders (dietary, other), linear regression analyses showed inverse relationship of total omega-3 PFA from food (percent kilocalories, from four 24-hour dietary recalls) to systolic and diastolic blood pressures. With adjustment for 17 variables, estimated systolic blood pressure/diastolic blood pressure differences with 2 standard deviation higher (0.67% kcal) omega-3 PFA were 0.55/0.57 mm Hg (Z-score 1.33, 2.00); for 2238 persons without medical or dietary intervention, 1.01/0.98 mm Hg (Z 1.63, 2.25); for 2038 nonhypertensive persons from this sub-cohort, 0.91/0.92 mm Hg (Z 1.80, 2.38). For linolenic acid (largely from vegetable foods), blood pressure differences were similar, eg, for the 2238 �nonintervened� individuals, 0.97/0.87 mm Hg (Z 1.52, 1.95); blood pressure differences were 0.32/0.45 mm Hg for long-chain omega-3 PFA (largely from fish). In summary, food omega-3 PFA intake related inversely to blood pressure, including in nonhypertensive persons, with small estimated effect size. Food omega-3 PFA may contribute to prevention and control of adverse blood pressure levels. (Author�s abstract)
Inconsistencies in the literature prevail regarding the role of n-3 PFA on blood pressure (BP). Meta-analyses of randomized clinical trials (RCTs) have reported significant BP reduction overall and in hypertensive participants; significant heterogeneity in systolic BP (SBP) outcomes across trials; only small nonsignificant systolic and diastolic BP (DBP) lowering in nonhypertensive individuals. The authors suggest that in order to detect the effects of single nutrients on BP of individuals, it is essential to collect standardized, high-quality data on large samples of diverse populations. Thus the INTERMAP surveyed in-depth 4680 men and women ages 40 to 59 from 17 population samples in Japan, People�s Republic of China, United Kingdom, United States to determine: (1) Does food -3 PFA intake of individuals relate independently to their SBP/DBP? (2) Is this the case throughout the population, including nonhypertensive individuals? (3) Are both linolenic and long-chain n-3 PFA intake independently associated with their SBP/DBP? INTERMAP hypothesized that dietary -3 PFA intake of individuals is inversely related to their blood pressure. Consistent independent inverse relations of total n-3 PFA to systolic and diastolic pressure were reported with the estimated effect size small, 1.0 mm Hg with 2 SD higher n-3 PFA intake (about 1.9 g/d) and the estimated effect size larger for nonhypertensive persons and for persons not reporting lifestyle modification (eg, special diet, use of nutritional supplements), diagnosed CVD or diabetes, prescribed medication for major chronic disease. The study found similar inverse relations of linolenic acid to SBP/DBP and for long-chain n-3 PFA (EPA+DHA, EPA separately, DHA separately) a qualitatively similar weaker inverse relation to DBP. These INTERMAP observational data on food n-3 PFA and BP are concordant with results from meta-analyses of randomized trials assessing whether n-3 PFA supplements (mostly fish oil capsules) influence BP; the data are similar qualitatively and quantitatively in indicating a low-order favorable BP effect in nonhypertensive subjects. The authors surmise that the n-3 PFA-BP relationship may be etiologically significant. Possible mechanisms whereby n-3 PFA may favourably influence BP are, based on animal experimental data: enhanced endothelial vasodilator function, reduced reactivity of resistant vessel vascular smooth muscle, and increased vascular compliance. Estimates indicate that lowering of population average SBP by �small� amounts (eg, 2 mm Hg) can result in reduction of mortality rates of 6% for stroke and 4% for coronary heart disease (CHD). Enhanced n-3 PFA intake from foods may contribute to decreased risk of CHD/CVD not only by modestly lowering BP, also by favorably influencing dyslipidemia, by anticoagulant, and antiarrhythmic effects. In conclusion, there was a weak inverse relationship to BP of n-3 polyunsaturated fat intake from foods (total, linolenic acid, long-chain) with control for multiple possible confounders. This finding was stronger for nonhypertensive people and persons not experiencing dietary/medical intervention, ie, was stronger after removing sources of possible bias, a result consistent with the inference that the n-3 PFA�BP relationship may be etiologically significant, albeit low-order. (Editor�s comments)