Table 3.

Characteristics of the studies evaluating fish intake, n-3 LC-PUFA intake and fish oil supplements and hypertension

Author	Outcomes	Type of study	Exposure	Results	Conclusion
Campbell et al., 2012 Eur J Preventive cardiology	Effectiveness of fish-oil supplementation on BP	Systematic review of RCTs 17 RCTs N = 1,524 Normotensive and hypertensive participants (at least BP 140/85 mmHg)	Fish oil supplementation, range EPA+DHA; 0.8–5.08 g/day	8 studies in hypertensive participants found a statistically significant reduction in SBP; 2.56 mmHg (95% CI 0.58 to 4.53) and in DBP; 1.47 mmHg (95% CI 0.41 to 2.53) 9 studies in normotensive participants showed a non-significant reduction in both SBP and DBP.	Small reduction in BP among hypertensive participants
Miller et al., 2014 Am J Hypertension	Examine the effect of EPA+DHA, without upper dose limits and including food sources on blood pressure	MA of RCTs 70 RCTs included	Fish oil supplementation, range EPA-DHA; 0.1–15.0 g/day	Compared to placebo, EPA+DHA reduced SBP -1.52 mmHg (95% CI -2.25 to -0.79) and DBP -0.99 mmHg (95% CI -1.54 to -0.44) The strongest effect were observed among untreated hypertensive subjects, although blood pressure was lowered among normotensive subjects	Provision of EPA-DHA may reduce SBP and provision of ≥2 g reduced DBP.
Yang et al., 2016 Nutrients	Elevated blood pressure Defined as SBP≥140 mm Hg or DBP≥90 mm Hg in four studies and as SBP≥130 mm Hg or DBP≥85 mm Hg in four studies	MA 8 cohort studies N = 56,204 adults and n = 20,497 elevated blood pressure events Follow-up from 3 to 20 years	Comparing highest versus lowest fish intake, 4 cohort studies, n = 17,710 and n = 3,590 cases Comparing highest versus lowest n-3 LC-PUFA intake , 6 cohort studies, (three studies for biomarkers and three studies for diet), n = 38,494 and n = 16,907 cases Comparing highest versus lowest n-3 LC-PUFA intake, 3 cohort studies, (studies for diet), n = 36,112 and n = 15,245 cases	Highest versus lowest intake and RR (95% CI) for hypertension 0.96 (0.81 to 1.14), I2 = 44.7%; P-heterogeneity = 0.143 Each 20 g/day increment of fish consumption was not significantly associated with reduced risk of elevated BP RR 0.98 (0.94 to 1.03) Highest versus lowest n-3 LC-PUFA category and RR (95% CI) for hypertension 0.73 (0.60 to 0.89), I2 = 75%; P-heterogeneity = 0.001 Highest versus lowest n-3 LC-PUFA intake and RR (95% CI) for hypertension 0.80 (0.58 to 1.10), I2 = 79.3%; P-heterogeneity = 0.002	No association between fish or dietary n-3 LC-PUFA intake and incidence of elevated BP. Circulating n-3 LC-PUFA as biomarkers of dietary intake are inversely associated with incidence of elevated BP. No association between high and low intake of n-3 LC-PUFA
Schwingshackl et al., 2017 Adv Nutr	Risk of hypertension The incidence of hypertension was defined as SBP≥140 mm Hg or DBP≥90 mm Hg for the first time in any follow-up checkup or when taking antihypertensive medication for the first time in the follow-up visits	SR and MA 8 prospective cohort, case-cohort, and nested case–control studies, and follow-ups of RCTs N = 83,612 incident cases	Comparing extreme fish intake categories (range of intake 0–156 g/day)	Highest versus lowest intake and RR (95% CI) for hypertension 1.01 (0.92 to 1.10), I 2 = 57%; P-heterogeneity = 0.02 An increase in fish intake by 100 g/day and RR (95% CI) for hypertension 1.07 (0.98 to 1.16), I2 = 74%; P-heterogeneity < 0.0001 Nonlinear dose-response association (P-nonlinearity < 0.01; n = 7 studies) Risk increased by 8% with increasing intake of fish ≤100 g/day	No association between high and low intake of fish, and dose-response Fish consumption was associated with a slight increase in hypertension risk in the nonlinear dose-response analysis.
Alhassan et al., 2017 Atherosclerosis	Vascular risk factors. Primary outcomes included lipid biomarkers (TG, TC, HDL-C, LDL-C, VLDL-C, SBP, DBP, glucose, insulin, HOMA-IR, inflammation markers	SR and MA 14 clinical trials and RCTs N = 1,378 adults (>18 years) Mean follow up for 9 weeks (4–24 weeks)	Fish intake-the frequencies for consuming fish ranged from once a week to daily consumption, and portion size of oily fish (most commonly salmon), consumed on a given day ranged from 20 to 500 g.		No effect of fish consumption on blood pressure
Abdelhamid et al., 2020 Cochrane Database Syst Rev	TC TG HDL-C LDL-C DBP SBP	SR and MA 30 RCTs 28 RCTs 30 RCTs 25 RCTs 15 RCTs 17 RCTs	Fish oil supplementation (mainly), dietary intake Comparing high versus low long chain n-3 fatty acid intake	No effect on DBP mean difference -0.02 (95% CI -0.22 to 0.17) No effect on SBP mean difference 0.01 (95% CI -0.31 to 0.34)	No effect of fish oil supplementation on DBP and SBP

BP, blood pressure; SBP, systolic blood pressure; DBP, diastolic blood pressure; SR, systematic review; MA, meta-analysis; RCT, randomized controlled trial; HR, Hazard ratio; OR, Odds ratio; RR, Relative risk/Risk ratio.