Omega-3 fatty acid supplementation augments sympathetic nerve activity responses to physiological stressors in humans

Genetics of Neurogenic Orthostatic Hypotension in Parkinson’s Disease, Results from a Cross-Sectional In Silico Study

The genetic basis of Neurogenic Orthostatic Hypotension (NOH) in Parkinson’s disease (PD) has been inadequately explored. In a cross-sectional study, we examined the association between NOH and PD-related single-nucleotide polymorphisms (SNPs) and mapped their effects on gene expression and metabolic and signaling pathways. Patients with PD, free from pathological conditions associated with OH, and not taking OH-associated medications were included. NOH was defined as per international guidelines. Logistic regression was used to relate SNPs to NOH. Linkage-disequilibrium analysis, expression quantitative trait loci, and enrichment analysis were used to assess the effects on gene expression and metabolic/signaling pathways. We included 304 PD patients in the study, 35 of whom had NOH (11.5%). NOH was more frequent in patients with SNPs in SNCA, TMEM175, FAM47E-STBD1, CCDC62, SCN3A, MIR4696, SH3GL2, and LZTS3/DDRGK1 and less frequent in those with SNPs in ITGA8, IP6K2, SIPA1L2, NDUFAF2. These SNPs affected gene expression associated with the significant hierarchical central structures of the autonomic nervous system. They influenced several metabolic/signaling pathways, most notably IP3/Ca++ signaling, the PKA-CREB pathway, and the metabolism of fatty acids. These findings provide new insights into the pathophysiology of NOH in PD and may provide targets for future therapies.

Omega-3 Polyunsaturated Fatty Acids Intake and Blood Pressure: A Dose-Response Meta-Analysis of Randomized Controlled Trials

Background

Current evidence might support the use of omega‐3 fatty acids (preferably docosahexaenoic acid and eicosapentaenoic acid) for lowering blood pressure (BP), but the strength and shape of the dose‐response relationship remains unclear.

Methods and Results

This study included randomized controlled trials published before May 7, 2021, that involved participants aged ≥18 years, and examined an association between omega‐3 fatty acids (docosahexaenoic acid, eicosapentaenoic acid, or both) and BP. A random‐effects 1‐stage cubic spline regression model was used to predict the average dose‐response association between daily omega‐3 fatty acid intake and changes in BP. We also conducted stratified analyses to examine differences by prespecified subgroups. Seventy‐one trials were included, involving 4973 individuals with a combined docosahexaenoic acid+eicosapentaenoic acid dose of 2.8 g/d (interquartile range, 1.3 g/d to 3.6 g/d). A nonlinear association was found overall or in most subgroups, depicted as J‐shaped dose‐response curves. The optimal intake in both systolic BP and diastolic BP reductions (mm Hg) were obtained by moderate doses between 2 g/d (systolic BP, −2.61 [95% CI, −3.57 to −1.65]; diastolic BP, −1.64 [95% CI, −2.29 to −0.99]) and 3 g/d (systolic BP, −2.61 [95% CI, −3.52 to −1.69]; diastolic BP, −1.80 [95% CI, −2.38 to −1.23]). Subgroup studies revealed stronger and approximately linear dose‐response relations among hypertensive, hyperlipidemic, and older populations.

Conclusions

This dose‐response meta‐analysis demonstrates that the optimal combined intake of omega‐3 fatty acids for BP lowering is likely between 2 g/d and 3 g/d. Doses of omega‐3 fatty acid intake above the recommended 3 g/d may be associated with additional benefits in lowering BP among groups at high risk for cardiovascular diseases.

Exploring the effects of oily fish consumption on measures of acute and long-term stress in healthy 8-9-year-old children: the FiSK Junior randomised trial

Long-chain n-3 PUFA (n-3 LCPUFA) are known to reduce blood pressure (BP), heart rate and vagal tone, but potential stress-mitigating effects of n-3 LCPUFA are not well investigated. We explored the effects of oily fish consumption on long-term stress and the stress response in schoolchildren. Healthy 8-9-year-old children were randomised to receive about 300 g/week of oily fish or poultry for 12 weeks (199 randomised, 197 completing). At baseline and endpoint, we measured erythrocyte n-3 LCPUFA, hair cortisol and the response to a 1-min cold pressor test (CPT) on saliva cortisol, BP and continuous electrocardiogram recordings. Post-intervention hair cortisol did not differ between the groups, but sex-specificity was indicated (Psex × group = 0·074, boys: -0·9 (95 % CI -2·9, 1·0) ng/g, girls: 0·7 (95 % CI -0·2, 1·6) ng/g). Children in the fish group tended to be less prone to terminate CPT prematurely (OR 0·20 (95 % CI 0·02, 1·04)). Mean heart beat interval during CPT was 18·2 (95 % CI 0·3, 36·6) ms longer and high frequency power increased (159 (95 % CI 29, 289) ms2) in the fish v. poultry group. The cardiac autonomic response in the 10 min following CPT was characterised by a sympathetic peak followed by a parasympathetic peak, which was most pronounced in the fish group. This exploratory study does not support a strong effect of oily fish consumption on stress but indicates that oily fish consumption may increase vagal cardiac tone during the physiological response to CPT. These results warrant further investigation.

DHA-Rich Fish Oil Increases the Omega-3 Index in Healthy Adults and Slows Resting Heart Rate without Altering Cardiac Autonomic Reflex Modulation

Regular fish consumption, a rich source of long-chain omega-3 (ω-3) docosahexaenoic acid (DHA), modifies cardiac electrophysiology. However, human studies investigating fish oil and cardiac electrophysiology have predominantly supplemented therapeutic (high) doses of fish oil (often ω-3 eicosapentaenoic acid (EPA) rich sources). This study examined whether non-therapeutic doses of DHA-rich fish oil modulate cardiac electrophysiology at rest and during cardiovascular reflex challenges to the same extent, if at all, in young healthy adults.

Participants (N = 20) were supplemented (double-blinded) with (2x1g.day^-1) soy oil (Control n = 9) or DHA-rich tuna fish oil (FO n = 11) providing DHA: 560 mg and EPA: 140 mg. The Omega-3 Index (O3I; erythrocyte membrane % EPA + DHA), heart rate (HR) and HR variability (HRV) were analyzed during rest, maximal isometric handgrip and cold diving reflex challenges at baseline and following 8 weeks.

The baseline O3I (Control: 5.1 ± 1.0; FO: 5.4 ± 0.9; P > 0.05), resting HR (Control: 65 ± 12bpm; FO: 66 ± 8bpm; P > 0.05) and HRV metrics did not significantly differ between the groups prior to supplementation. Relative to the control group, the O3I was increased (Control: 5.0 ± 1.1; FO: 7.8 ± 1.2; P < 0.001), and resting HR was slowed in the FO group following supplementation (Control: 66 ± 9bpm; FO: 61 ± 6bpm; P = 0.046). However, no significant (P > 0.05) between-group differences were observed in HR responsiveness or any indices of HRV during reflex challenges.

In young healthy adults, dietary achievable doses of ω-3 DHA-rich fish oil exerted a direct slowing effect on resting HR, without compromising the HR response to either dominant sympathetic or parasympathetic modulation.

Omega-3 supplementation and stress reactivity of cellular aging biomarkers: an ancillary substudy of a randomized, controlled trial in midlife adults

Higher levels of omega-3 track with longer telomeres, lower inflammation, and blunted sympathetic and cardiovascular stress reactivity. Whether omega-3 supplementation alters the stress responsivity of telomerase, cortisol, and inflammation is unknown. This randomized, controlled trial examined the impact of omega-3 supplementation on cellular aging-related biomarkers following a laboratory speech stressor. In total, 138 sedentary, overweight, middle-aged participants (n = 93 women, n = 45 men) received either 2.5 g/d of omega-3, 1.25 g/d of omega-3, or a placebo for 4 months. Before and after the trial, participants underwent the Trier Social Stress Test. Saliva and blood samples were collected once before and repeatedly after the stressor to measure salivary cortisol, telomerase in peripheral blood lymphocytes, and serum anti-inflammatory (interleukin-10; IL-10) and pro-inflammatory (interleukin-6; IL-6, interleukin-12, tumor necrosis factor-alpha) cytokines. Adjusting for pre-supplementation reactivity, age, sagittal abdominal diameter, and sex, omega-3 supplementation altered telomerase (p = 0.05) and IL-10 (p = 0.05) stress reactivity; both supplementation groups were protected from the placebo group's 24% and 26% post-stress declines in the geometric means of telomerase and IL-10, respectively. Omega-3 also reduced overall cortisol (p = 0.03) and IL-6 (p = 0.03) throughout the stressor; the 2.5 g/d group had 19% and 33% lower overall cortisol levels and IL-6 geometric mean levels, respectively, compared to the placebo group. By lowering overall inflammation and cortisol levels during stress and boosting repair mechanisms during recovery, omega-3 may slow accelerated aging and reduce depression risk. ClinicalTrials.gov identifier: NCT00385723.

Omega-3 polyunsaturated fatty acid oral supplements for improving peripheral nerve health: a systematic review and meta-analysis

CONTEXT

Peripheral nerve damage can occur in a variety of systemic conditions and can have a profound impact on functional and psychological health. Currently, therapeutic interventions for peripheral nerve damage are limited.

OBJECTIVE

The aim of this systematic review, conducted in accordance with the Cochrane Collaboration's handbook and reported according to the PRISMA checklist, was to evaluate the efficacy and safety of omega-3 oral supplements for improving peripheral nerve structure and function.

DATA SOURCES

PubMed, Embase, and Cochrane databases, along with clinical trial registries, were searched from inception to February 2019. Evidence was identified, critically appraised, and synthesized, and the certainty of evidence was appraised using the Grading of Recommendations Assessment, Development and Evaluation approach.

STUDY SELECTION

Randomized controlled trials assessing the effects of omega-3 oral supplementation on outcomes of peripheral nerve structure, peripheral nerve function, or both were eligible for inclusion. Titles and abstracts of identified articles were independently assessed for potential eligibility by 2 review authors. For studies judged as eligible or potentially eligible, full text articles were retrieved and independently assessed by 2 review authors to determine eligibility; disagreements were resolved by consensus.

DATA EXTRACTION

Fifteen trials were included. Two clinically similar studies that investigated the effect of omega-3 supplementation in individuals receiving chemotherapy were meta-analyzed. Pooled data showed a reduced incidence of peripheral neuropathy (RR = 0.58; 95%CI, 0.43-0.77) and a preservation of sensory nerve action potential amplitudes with omega-3 supplementation compared with placebo (MD = 4.19 µV; 95%CI; 2.19-6.19).

CONCLUSION

This review finds, with low certainty, that omega-3 supplementation attenuates sensory loss and reduces the incidence of neuropathy secondary to oxaliplatin and paclitaxel treatment relative to placebo. There is currently limited evidence to ascertain whether omega-3 supplementation is beneficial in other systemic conditions characterized by peripheral nerve damage.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD 42018086297.

Membrane modulatory effects of omega-3 fatty acids: Analysis of molecular level interactions

Bioactive omega-3 polyunsaturated fatty acids have been shown to reduce the risk of death in patients with cardiovascular disease and alleviate the symptoms of other inflammatory diseases. However, the mechanisms of action of these effects remain unclear. It has been postulated that omega-3 polyunsaturated fatty acids modify cell membranes by incorporation into the membrane and altering the signaling properties of cellular receptors. In this chapter, we explore the effects of omega-3 polyunsaturated fatty acids on cell membrane structure and function. We present a review of the current evidence for the health benefits of these compounds and explore the molecular mechanisms through which omega-3 polyunsaturated fatty acids interact with membrane lipids and modulate bilayer structure. Using computational models of multicomponent phospholipid bilayers, we assess the consequences of incorporation of these fatty acids on membrane lipid packing, water permeation, and membrane structure.

Docosahexaenoic acid reduces resting blood pressure but increases muscle sympathetic outflow compared with eicosapentaenoic acid in healthy men and women

Supplementation with monounsaturated or ω-3 polyunsaturated fatty acids ( n-3 PUFA) can lower resting blood pressure (BP) and reduce the risk of cardiovascular events. The independent contributions of the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on BP, and the mechanisms responsible, are unclear. We tested whether EPA, DHA, and olive oil (OO), a source of monounsaturated fat, differentially affect resting hemodynamics and muscle sympathetic nerve activity (MSNA). Eighty-six healthy young men and women were recruited to participate in a 12-wk, randomized, double-blind trial examining the effects of orally supplementing ~3 g/day of EPA ( n = 28), DHA ( n = 28), or OO ( n = 30) on resting hemodynamics; MSNA was examined in a subset of participants ( n = 31). Both EPA and DHA supplements increased the ω-3 index ( P < 0.01). Reductions in systolic BP were greater [adjusted intergroup mean difference (95% confidence interval)] after DHA [−3.4 mmHg (−0.9, −5.9), P = 0.008] and OO [−3.0 mmHg (−0.5, −5.4), P = 0.01] compared with EPA, with no difference between DHA and OO ( P = 0.74). Reductions in diastolic BP were greater following DHA [−3.4 mmHg (−1.3,−5.6), P = 0.002] and OO [−2.2 mmHg (0.08,−4.3), P = 0.04] compared with EPA. EPA increased heart rate compared with DHA [4.2 beats/min (−0.009, 8.4), P = 0.05] and OO [4.2 beats/min, (0.08, 8.3), P = 0.04]. MSNA burst frequency was higher after DHA [4 bursts/min (0.5, 8.3), P = 0.02] but not OO [−3 bursts/min (−6, 0.6), P = 0.2] compared with EPA. Overall, DHA and OO evoked similar responses in resting BP; however, DHA, but not OO, increased peripheral vasoconstrictor outflow. These findings may have implications for fatty acid supplementation in clinical populations characterized by chronic high BP and sympathetic overactivation.

NEW & NOTEWORTHY We studied the effects of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and olive oil supplementation on blood pressure (BP) and muscle sympathetic nerve activity (MSNA). After 12 wk of 3 g/day supplementation, DHA and olive oil were associated with lower resting systolic and diastolic BPs than EPA. However, DHA increased MSNA compared with EPA. The reductions in BP with DHA likely occur via a vascular mechanism and evoke a baroreflex-mediated increase in sympathetic activity.

Omega-3 polyunsaturated fatty acid supplementation reduces blood pressure but not renal vasoconstrictor response to orthostatic stress in healthy older adults

Older adults exhibit augmented renal vasoconstriction during orthostatic stress compared to young adults. Consumption of omega-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oil (FO), modulates autonomic nerve activity. However, the effect of omega-3 polyunsaturated fatty acid consumption on the renal vasoconstrictor response to orthostatic stress in young and older adults is unknown. Therefore, 10 young (25 ± 1 years; mean ± SEM) and 10 older (66 ± 2 years) healthy adults ingested 4 g FO daily for 12 weeks, and underwent graded lower body negative pressure (LBNP; -15 and -30 mmHg) pre- and post-FO supplementation. Renal blood flow velocity (RBFV; Doppler ultrasound), arterial blood pressure (BP; photoplethysmographic finger cuff), and heart rate (electrocardiogram) were recorded. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as mean BP/RBFV. All baseline cardiovascular values were similar between groups and visits, except diastolic BP was higher in the older group (P < 0.05). FO supplementation increased erythrocyte EPA and DHA content in both groups (P < 0.05). FO did not affect RVR or RBFV responses to LBNP in either group, but attenuated the mean BP response to LBNP in the older group (older -30 mmHg: pre-FO -4 ± 1 vs. post-FO 0 ± 1 mmHg, P < 0.05; young -30 mmHg: pre-FO -5 ± 1 vs. post-FO -5 ± 2 mmHg). In conclusion, FO supplementation attenuates the mean BP response but does not affect the renal vasoconstrictor response to orthostatic stress in older adults.

Effect of omega-3 long-chain polyunsaturated fatty acid supplementation on heart rate: a meta-analysis of randomized controlled trials

Background

Elevated resting heart rate (HR) has emerged as a new risk factor for all-cause and cardiovascular mortality. The effect of marine-derived omega-3 long-chain polyunsaturated fatty acid (n−3 LCPUFAs) supplementation on HR was investigated as an outcome in many clinical trials. The present study was to provide an updated meta-analysis on the HR-slowing effect of n−3 LCPUFAs, and to differentiate the chronotropic effect between eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Methods

PubMed and Cochrane databases were searched for relevant articles examining the effects of n−3 PUFAs on HR through May 2017. A random-effects model was used to generate the pooled effect sizes and 95% confidence intervals (CIs). The pooled effect sizes were presented as weighted mean differences (WMDs).

Results

A total of 51 randomized controlled trials (RCTs) with approximately 3000 participants were included in this meta-analysis. Compared to placebo, n−3 PUFA supplementation mildly but significantly reduced HR (−2.23 bpm; 95% CI: −3.07, −1.40 bpm). Moderate evidence of heterogeneity was observed among included trials (I² = 49.1%, P heterogeneity < 0.001). When DHA and EPA were separately administered, modest HR reduction was observed in trials that supplemented with DHA (−2.47 bpm; 95% CI: −3.47, −1.46 bpm), but not in trials with EPA.

Conclusions

The present meta-analysis provides strong clinical evidence demonstrating the effect of heart rate reduction by n−3 LCPUFA supplementation. When DHA or EPA administered alone, heart rate was slowed by DHA rather than by EPA.

Modulation of heart rate and heart rate variability by n-3 long chain polyunsaturated fatty acids: Speculation on mechanism(s)

Heart rate (HR) and heart rate variability (HRV) are valuable markers of health. Although the underlying mechanism(s) are controversial, it is well documented that n-3 long chain polyunsaturated fatty acid (LCPUFA) intake improves HR and HRV in various populations. Autonomic modulation and/or alterations in cardiac electrophysiology are commonly cited as potential mechanisms responsible for these effects. This article reviews existing evidence for each and explores a separate mechanism which has not received much attention but has scientific merit. Based on presented evidence, it is proposed that n-3 LCPUFAs affect HR and HRV directly by autonomic modulation and indirectly by altering circulating factors, both dependently and independently of the autonomic nervous system. The evidence for changes in cardiac electrophysiology as the mechanism by which n-3 LCPUFAs affect HR and HRV needs strengthening.

Acute beetroot juice supplementation on sympathetic nerve activity: a randomized, double-blind, placebo-controlled proof-of-concept study

Acute dietary nitrate ([Formula: see text]) supplementation reduces resting blood pressure in healthy normotensives. This response has been attributed to increased nitric oxide bioavailability and peripheral vasodilation, although nitric oxide also tonically inhibits central sympathetic outflow. We hypothesized that acute dietary [Formula: see text] supplementation using beetroot (BR) juice would reduce blood pressure and muscle sympathetic nerve activity (MSNA) at rest and during exercise. Fourteen participants (7 men and 7 women, age: 25 ± 10 yr) underwent blood pressure and MSNA measurements before and after (165–180 min) ingestion of 70ml high-[Formula: see text] (~6.4 mmol [Formula: see text]) BR or [Formula: see text]-depleted BR placebo (PL; ~0.0055 mmol [Formula: see text]) in a double-blind, randomized, crossover design. Blood pressure and MSNA were also collected during 2 min of static handgrip (30% maximal voluntary contraction). The changes in resting MSNA burst frequency (−3 ± 5 vs. 3 ± 4 bursts/min, P = 0.001) and burst incidence (−4 ± 7 vs. 4 ± 5 bursts/100 heart beats, P = 0.002) were lower after BR versus PL, whereas systolic blood pressure (−1 ± 5 vs. 2 ± 5 mmHg, P = 0.30) and diastolic blood pressure (4 ± 5 vs. 5 ± 7 mmHg, P = 0.68) as well as spontaneous arterial sympathetic baroreflex sensitivity ( P = 0.95) were not different. During static handgrip, the change in MSNA burst incidence (1 ± 8 vs. 8 ± 9 bursts/100 heart beats, P = 0.04) was lower after BR versus PL, whereas MSNA burst frequency (6 ± 6 vs. 11 ± 10 bursts/min, P = 0.11) as well as systolic blood pressure (11 ± 7 vs. 12 ± 8 mmHg, P = 0.94) and diastolic blood pressure (11 ± 4 vs. 11 ± 4 mmHg, P = 0.60) were not different. Collectively, these data provide proof of principle that acute BR supplementation can decrease central sympathetic outflow at rest and during exercise. Dietary [Formula: see text] supplementation may represent a novel intervention to target exaggerated sympathetic outflow in clinical populations.

NEW & NOTEWORTHY The hemodynamic benefits of dietary nitrate supplementation have been attributed to nitric oxide-mediated peripheral vasodilation. Here, we provide proof of concept that acute dietary nitrate supplementation using beetroot juice can decrease muscle sympathetic outflow at rest and during exercise in a normotensive population. These results have applications for targeting central sympathetic overactivation in disease.

Omega-3 polyunsaturated fatty acid supplementation attenuates blood pressure increase at onset of isometric handgrip exercise in healthy young and older humans

Aging is associated with alterations of autonomic nerve activity, and dietary intake of omega-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oil (FO), can modulate autonomic nerve activity. However, the effect of omega-3 polyunsaturated fatty acid consumption on age-related cardiovascular responses at the onset of isometric handgrip exercise, a time of rapid autonomic adjustments, is unknown. Accordingly, 14 young (25 ± 1 years; mean ± SE) and 15 older (64 ± 2 years) healthy subjects ingested 4 g FO daily for 12 weeks. On pre- and postintervention visits, participants performed 15-sec bouts of isometric handgrip at 10%, 30%, 50%, and 70% maximal voluntary contraction (MVC) while beat-to-beat systolic, diastolic, and mean arterial blood pressure (SBP, DBP, MAP; Finometer) and heart rate (HR; electrocardiogram) were recorded. All baseline cardiovascular variables were similar between groups and visits, except DBP was higher in older subjects (P < 0.05). FO increased erythrocyte EPA and DHA content in both groups (P < 0.05). FO attenuated MAP and DBP increases in response to handgrip in both age groups (change from baseline during 70% MVC handgrip pre- and post-FO: young MAPΔ 14 ± 2 mmHg versus 10 ± 2 mmHg, older MAPΔ 14 ± 3 mmHg versus 11 ± 2 mmHg; young DBPΔ 12 ± 1 mmHg versus 7 ± 2 mmHg, older DBPΔ 12 ± 1 mmHg versus 7 ± 1 mmHg; P < 0.05). FO augmented the PP (SBP-DBP) increase with 70% MVC handgrip in both groups (P < 0.05), but did not alter SBP or HR increases with handgrip. These findings suggest that FO supplementation attenuates MAP and DBP increases at the onset of isometric handgrip exercise in healthy young and older humans.

Obesity-associated sympathetic overactivity in children and adolescents: the role of catecholamine resistance in lipid metabolism

BACKGROUND

Obesity in children and adolescents is characterized by chronic sympathetic overdrive and reduced epinephrine-stimulated lipolysis. This resistance to catecholamines occurs during the dynamic phase of fat accumulation. This review will focus on the relationship between sympathetic-adrenal activity and lipid metabolism, thereby highlighting the role of catecholamine resistance in the development of childhood obesity.

RESULTS AND CONCLUSIONS

Catecholamine resistance causes lipid accumulation in adipose tissue by reducing lipolysis, increasing lipogenesis and impeding free fatty acid (FFA) transportation. Exercise improves catecholamine resistance, as evidenced by attenuated systemic sympathetic activity, reduced circulating catecholamine levels and enhanced β-adrenergic receptor signaling. Insulin resistance is mostly a casual result rather than a cause of childhood obesity. Therefore, catecholamine resistance in childhood obesity may promote insulin signaling in adipose tissue, thereby increasing lipogenesis. This review outlines a series of evidence for the role of catecholamine resistance as an upstream mechanism leading to childhood obesity.

Effect of omega-3 polyunsaturated fatty acid supplementation on central arterial stiffness and arterial wave reflections in young and older healthy adults

Increased central arterial stiffness and enhanced arterial wave reflections may contribute to increased risk of cardiovascular disease development with advancing age. Omega-3 polyunsaturated fatty acid (n-3) ingestion may reduce cardiovascular risk via favorable effects exerted on arterial structure and function. We determined the effects of n-3 supplementation (4 g/day for 12 weeks) on important measures of central arterial stiffness (carotid-femoral pulse wave velocity; PWV) and arterial wave reflection (central augmentation index) in young (n = 12; 25 ± 1-year-old, mean ± SE) and older (n = 12; 66 ± 2) healthy adults. We hypothesized that n-3 supplementation would decrease carotid-femoral PWV and central augmentation index in older adults. Our results indicate that carotid-femoral PWV and central augmentation index were greater in older (988 ± 65 cm/sec and 33 ± 2%) than in young adults (656 ± 16 cm/sec and 3 ± 4%: both P < 0.05 compared to older) before the intervention (Pre). N-3 supplementation decreased carotid-femoral PWV in older (∆-9 ± 2% Precompared to Post; P < 0.05), but not young adults (∆2 ± 3%). Central augmentation index was unchanged by n-3 supplementation in young (3 ± 4 vs. 0 ± 4% for Pre and Post, respectively) and older adults (33 ± 2 vs. 35 ± 3%). Arterial blood pressure at rest, although increased with age, was not altered by n-3 supplementation in young or older adults. Collectively, these data indicate that 12 weeks of daily n-3 supplementation decreases an important measure of central arterial stiffness (carotid-femoral PWV) in older, but not young healthy adults. The mechanism underlying decreased central arterial stiffness with n-3 supplementation is unknown, but appears to be independent of effects on arterial blood pressure or arterial wave reflections.

Long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and blood pressure: a meta-analysis of randomized controlled trials

BACKGROUND

Although a large body of literature has been devoted to examining the relationship between eicosapentaenoic and docosahexaenoic acids (EPA+DHA) and blood pressure, past systematic reviews have been hampered by narrow inclusion criteria and a limited scope of analytical subgroups. In addition, no meta-analysis to date has captured the substantial volume of randomized controlled trials (RCTs) published in the past 2 years. The objective of this meta-analysis was to examine the effect of EPA+DHA, without upper dose limits and including food sources, on blood pressure in RCTs.

METHODS

Random-effects meta-analyses were used to generate weighted group mean differences and 95% confidence intervals (CIs) between the EPA+DHA group and the placebo group. Analyses were conducted for subgroups defined by key subject or study characteristics.

RESULTS

Seventy RCTs were included. Compared with placebo, EPA+DHA provision reduced systolic blood pressure (−1.52mm Hg; 95% confidence interval (CI) = −2.25 to −0.79) and diastolic blood pressure (−0.99mm Hg; 95% CI = −1.54 to −0.44) in the meta-analyses of all studies combined. The strongest effects of EPA+DHA were observed among untreated hypertensive subjects (systolic blood pressure = −4.51mm Hg, 95% CI = −6.12 to −2.83; diastolic blood pressure = −3.05mm Hg, 95% CI = −4.35 to −1.74), although blood pressure also was lowered among normotensive subjects (systolic blood pressure = −1.25mm Hg, 95% CI = −2.05 to −0.46; diastolic blood pressure = −0.62mm Hg, 95% CI = −1.22 to −0.02).

CONCLUSIONS

Overall, available evidence from RCTs indicates that provision of EPA+DHA reduces systolic blood pressure, while provision of ≥2 grams reduces diastolic blood pressure.

The effects of dietary fish oil on exercising skeletal muscle vascular and metabolic control in chronic heart failure rats

Impaired vasomotor control in chronic heart failure (CHF) is due partly to decrements in nitric oxide synthase (NOS) mediated vasodilation. Exercising muscle blood flow (BF) is augmented with polyunsaturated fatty acid (PUFA) supplementation via fish oil (FO) in healthy rats. We hypothesized that FO would augment exercising muscle BF in CHF rats via increased NO-bioavailability. Myocardial infarction (coronary artery ligation) induced CHF in Sprague-Dawley rats which were subsequently randomized to dietary FO (20% docosahexaenoic acid, 30% eicosapentaenoic acid, n = 15) or safflower oil (SO, 5%, n = 10) for 6-8 weeks. Mean arterial pressure (MAP), blood [lactate], and hindlimb muscles BF (radiolabeled microspheres) were determined at rest, during treadmill exercise (20 m·min(-1), 5% incline) and exercise + N(G)-nitro-l-arginine-methyl-ester (l-NAME) (a nonspecific NOS inhibitor). FO did not change left ventricular end-diastolic pressure (SO: 14 ± 2; FO: 11 ± 1 mm Hg, p > 0.05). During exercise, MAP (SO: 128 ± 3; FO: 132 ± 3 mm Hg) and blood [lactate] (SO: 3.8 ± 0.4; FO: 4.6 ± 0.5 mmol·L(-1)) were not different (p > 0.05). Exercising hindlimb muscle BF was lower in FO than SO (SO: 120 ± 11; FO: 93 ± 4 mL·min(-1)·100 g(-1), p < 0.05) but was not differentially affected by l-NAME. Specifically, 17 of 28 individual muscle BF's were lower (p < 0.05) in FO demonstrating that PUFA supplementation with FO in CHF rats does not augment muscle BF during exercise but may lower metabolic cost.

The effects of omega-3 polyunsaturated fatty acids on cardiac rhythm: a critical reassessment

Although epidemiological studies provide strong evidence for an inverse relationship between omega-3 polyunsaturated fatty acids (n-3 PUFAs) and cardiac mortality, inconsistent and often conflicting results have been obtained from both animal studies and clinical prevention trials. Despite these heterogeneous results, some general conclusions can be drawn from these studies: 1) n-PUFAs have potent effects on ion channels and calcium regulatory proteins that vary depending on the route of administration. Circulating (acute administration) n-3 PUFAs affect ion channels directly while incorporation (long-term supplementation) of these lipids into cell membranes indirectly alter cardiac electrical activity via alteration of membrane properties. 2) n-3 PUFAs reduce baseline HR and increase HRV via alterations in intrinsic pacemaker rate rather than from changes in cardiac autonomic neural regulation. 3) n-3 PUFAs may be only effective if given before electrophysiological or structural remodeling has begun and have no efficacy against atrial fibrillation. 5) Despite initial encouraging results, more recent clinical prevention and animal studies have not only failed to reduce sudden cardiac death but actually increased mortality in angina patients and increased rather than decreased malignant arrhythmias in animal models of regional ischemia. 6) Given the inconsistent benefits reported in clinical and experimental studies and the potential adverse actions on cardiac rhythm noted during myocardial ischemia, n-3 PUFA must be prescribed with caution and generalized recommendations to increase fish intake or to take n-3 PUFA supplements need to be reconsidered.

Effects of marine-derived omega-3 fatty acids on systemic hemodynamics at rest and during stress: a dose-response study

BACKGROUND

Omega-3 fatty acids reduced heart rate (HR) and blood pressure (BP) in some studies, but dose-response studies are rare, and little is known about underlying mechanisms.

PURPOSE

We examined effects of 0.85 g/day eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) (low dose) and 3.4 g/day EPA + DHA (high dose) on HR and systemic hemodynamics during rest, speech, and foot cold pressor tasks.

METHODS

This was a dose-response, placebo-controlled, double-blind, randomized, crossover trial (8-week treatment, 6-week washout) in 26 adults.

RESULTS

Throughout the testing sessions, HR was reduced in a dose-dependent manner. The high dose reduced BP and stroke volume and increased pre-ejection period. Reductions in BP were associated with increases in erythrocyte omega-3 fatty acids.

CONCLUSIONS

High-dose long-chain omega-3 fatty acids can reduce BP and HR, at rest and during stress. These findings suggest that at-risk populations may achieve benefits with increased omega-3 intake. The trial was registered on ClinicalTrials.gov (NCT00504309).

Contribution of sympathetic activation to coronary vasodilatation during the cold pressor test in healthy men: effect of ageing

The sympathetic nervous system is an important regulator of coronary blood flow. The cold pressor test (CPT) is a powerful sympathoexcitatory stressor. We tested the hypotheses that: (1) CPT-induced sympathetic activation elicits coronary vasodilatation in young adults that is impaired with advancing age and (2) combined α- and β-adrenergic blockade diminishes/abolishes these age-related differences. Vascular responses of the left anterior descending artery to the CPT were determined by transthoracic Doppler echocardiography before (pre-blockade) and during (post-blockade) systemic co-administration of α- and β-adrenergic antagonists in young (n = 9; 26 ± 1 years old, mean ± SEM) and older healthy men (n = 9; 66 ± 2 years old). Coronary vascular resistance (CVR; mean arterial pressure/coronary blood velocity) was used as an index of vascular tone. CPT decreased CVR (i.e. coronary vasodilatation occurred) in young ( -33 ± 6%), but not older men ( -3 ± 4%; P < 0.05 vs. young) pre-blockade. Adrenergic blockade abolished CPT-induced coronary vasodilatation in young men ( -33 ± 6% vs. 0 ± 6%, pre-blockade vs. post-blockade, respectively; P < 0.05) such that responses post-blockade mirrored those of older men ( -3 ± 4% vs. 8 ± 9%; both P > 0.05 compared to young pre-blockade). Impaired CPT-induced coronary vasodilatation could not be explained by a reduced stimulus for vasodilatation as group and condition effects persisted when CVR responses were expressed relative to myocardial oxygen demand (rate-pressure product). These data indicate that the normal coronary vascular response to sympathetic activation in young men is pronounced vasodilatation and this effect is lost with age as the result of an adrenergic mechanism. These findings may help explain how acute sympathoexcitation may precipitate angina and coronary ischaemic events, particularly in older adults.

Fish oil and neurovascular reactivity to mental stress in humans

Omega-3 fatty acids found in fish oil have been suggested to protect against cardiovascular disease, yet underlying mechanisms remain unclear. Despite the well-documented link between mental stress and cardiovascular risk, no study has examined neural cardiovascular reactivity to mental stress after fish oil supplementation. We hypothesized that fish oil would blunt the blood pressure, heart rate (HR), and muscle sympathetic nerve activity (MSNA) responsiveness to mental stress and/or augment limb vasodilation associated with mental stress. Blood pressure, HR, MSNA, forearm vascular conductance (FVC), and calf vascular conductance (CVC) responses were recorded during a 5-min mental stress protocol in 67 nonhypertensive subjects before and after 8 wk of fish oil (n = 34) or placebo supplementation (n = 33). Fish oil blunted HR reactivity to mental stress (group × condition × time interactions, P = 0.012) but did not alter blood pressure reactivity to mental stress (interactions, P > 0.05). Fish oil blunted total MSNA reactivity to mental stress (interaction, P = 0.039) but did not alter MSNA burst frequency and burst incidence reactivity (interactions, P > 0.05). Finally, fish oil significantly blunted CVC reactivity to mental stress (interaction, P = 0.013) but did not alter FVC reactivity (interaction, P > 0.05). In conclusion, 8 wk of fish oil supplementation significantly attenuated both HR and total MSNA reactivity to mental stress and elicited a paradoxical blunting of calf vascular conductance. These findings support and extend the growing evidence that fish oil may have positive health benefits regarding neural cardiovascular control in humans.

Fish oil and neurovascular control in humans

The antihypertensive influence of fish oil is controversial, and the mechanisms remain unclear. Because the inverse relation between fish oil and hypertension appears to be partially dependent on the degree of hypertension, we tested the hypothesis that fish oil would elicit more dramatic reductions in mean arterial pressure (MAP) and muscle sympathetic nerve activity (MSNA) in prehypertensive (PHT) compared with normotensive (NT) subjects. Resting MAP, MSNA, and heart rate (HR) were examined before and after 8 wk of fish oil (9 g/day; 1.6 g eicosapentaenoic acid and 1.1 g docosahexaenoic acid) or placebo (olive oil; 9 g/day) in 38 NT (19 fish oil; 19 placebo) and 29 PHT (15 fish oil; 14 placebo) volunteers. Fish oil did not alter resting MAP, MSNA, or HR in either NT (80 ± 1 to 80 ± 1 mmHg; 11 ± 2 to 10 ± 1 bursts/min; 71 ± 2 to 71 ± 2 beats/min) or PHT (88 ± 2 to 87 ± 1 mmHg; 11 ± 2 to 10 ± 2 bursts/min; 73 ± 2 to 73 ± 2 beats/min) subjects. When NT and PHT groups were consolidated, analysis of covariance confirmed that pretreatment resting MAP was not associated with changes in MSNA after fish oil. In contrast, pretreatment resting HR was correlated with changes in MSNA (r = 0.47; P = 0.007) and MAP (r = 0.42; P < 0.007) after fish oil but not placebo. In conclusion, fish oil did not alter sympathetic neural control in NT or PHT subjects. However, our findings suggest that fish oil is associated with modest sympathoinhibition in individuals with higher resting heart rates, a finding that is consistent with a recent meta-analysis examining the relations among fish oil, HR, and the risk of cardiovascular disease.

Fatigue, inflammation, and ω-3 and ω-6 fatty acid intake among breast cancer survivors

PURPOSE

Evidence suggests that inflammation may drive fatigue in cancer survivors. Research in healthy populations has shown reduced inflammation with higher dietary intake of ω-3 polyunsaturated fatty acids (PUFAs), which could potentially reduce fatigue. This study investigated fatigue, inflammation, and intake of ω-3 and ω-6 PUFAs among breast cancer survivors.

METHODS

Six hundred thirty-three survivors (mean age, 56 years; stage I to IIIA) participating in the Health, Eating, Activity, and Lifestyle Study completed a food frequency/dietary supplement questionnaire and provided a blood sample assayed for C-reactive protein (CRP) and serum amyloid A (30 months after diagnosis) and completed the Piper Fatigue Scale and Short Form-36 (SF-36) vitality scale (39 months after diagnosis). Analysis of covariance and logistic regression models tested relationships between inflammation and fatigue, inflammation and ω-3 and ω-6 PUFA intake, and PUFA intake and fatigue, controlling for three incremental levels of confounders. Fatigue was analyzed continuously (Piper scales) and dichotomously (SF-36 vitality ≤ 50).

RESULTS

Behavioral (P = .003) and sensory (P = .001) fatigue scale scores were higher by increasing CRP tertile; relationships were attenuated after adjustment for medication use and comorbidity. Survivors with high CRP had 1.8 times greater odds of fatigue after full adjustment (P < .05). Higher intake of ω-6 relative to ω-3 PUFAs was associated with greater CRP (P = .01 after full adjustment) and greater odds of fatigue (odds ratio, 2.6 for the highest v lowest intake; P < .05).

CONCLUSION

Results link higher intake of ω-3 PUFAs, decreased inflammation, and decreased physical aspects of fatigue. Future studies should test whether ω-3 supplementation may reduce fatigue among significantly fatigued breast cancer survivors.

A comparison of the changes in cardiac output and systemic vascular resistance during exercise following high-fat meals containing DHA or EPA

Long-chain n-3 PUFA can lower blood pressure (BP) but their acute effects on cardiac output, BP and systemic vascular resistance (SVR) in response to dynamic exercise are uncertain. We compared the effects of high-fat meals rich in EPA (20 : 5n-3), DHA (22 : 6n-3) or oleic acid (control) on cardiac output, BP and SVR in response to exercise stress testing. High-fat meals (50 g fat) containing high-oleic sunflower oil enriched with 4·7 g of either EPA or DHA v. control (high-oleic sunflower oil only) were fed to twenty-two healthy males using a randomised cross-over design. Resting measurements of cardiac output, heart rate and BP were made before and hourly over 5 h following the meal. A standardised 12 min exercise test was then conducted with further measurements made during and post-exercise. Blood samples were collected at fasting, 5 h postprandially and immediately post-exercise for the analysis of lipid, glucose and 8-isoprostane-F2α (8-iso-PGF2α). Plasma concentrations of EPA and DHA increased by 0·22 mmol/l 5 h following the EPA and DHA meals, respectively, compared with the control (P < 0·001). Resting cardiac output and 8-iso-PGF2α increased similarly following all meals and there were no significant differences in cardiac output during exercise between the meals. SVR was lower at 5 h and during exercise following the DHA but not EPA meal, compared with the control meal, by 4·9 % (95 % CI 1·3, 8·4; P < 0·01). Meals containing DHA appear to differ from EPA with regard to their effects on cardiovascular haemodynamics during exercise.

Preliminary evidence that acute long-chain omega-3 supplementation reduces cardiovascular reactivity to mental stress: a randomized and placebo controlled trial

OBJECTIVE

Exaggerated cardiovascular reactivity predicts cardiovascular morbidity and mortality. Some evidence suggests that omega-3 fatty acids improve cardiovascular function. The objective of this study was to examine the influence of an acute low dose of long-chain omega-3 fatty acids on young, healthy individuals.

METHODS

Participants (n=34) were randomly assigned to either 21-days of omega-3 fatty acids (1.4 g EPA and DHA) or matched placebo. Cardiovascular measurements were obtained in the laboratory during baseline and during a standard mental arithmetic task, where participants were instructed to engage in serial subtractions by 17s from a four-digit number and cardiovascular reactivity to the task was calculated.

RESULTS

Mean arterial pressure reactivity was significantly reduced by supplementation (F(1,32)=5. 12, p=.03, η(2)=.144) but not by placebo.

CONCLUSION

Supplementation of omega-3 fatty acids may reduce cardiovascular reactivity to stress.

Genetic influences on blood pressure response to the cold pressor test: results from the Heredity and Phenotype Intervention Heart Study

OBJECTIVES

Blood pressure (BP) response to the cold pressor test (CPT) has been found to predict the development of hypertension and cardiovascular disease in prospective studies. The determinants of BP response to the CPT, including the role of genetic factors, however, are largely unknown. Additionally, to our knowledge, no study has examined the genetics of BP recovery from the CPT, including whether shared genetic factors influence both reactivity and recovery.

METHODS

As part of the Heredity and Phenotype Intervention Heart Study, we administered a 2.5 min hand CPT to 835 participants from 18 extended Amish families. We estimated the heritability of BP reactivity and recovery (measured by the incremental area under the curve) and the genetic correlations between baseline, reactivity, and recovery BP phenotypes.

RESULTS

After adjusting for relevant covariates, including baseline BP, the heritability estimates for both systolic BP (SBP) and diastolic BP (DBP) reactivity and recovery differed significantly from zero (P < 0.01), with 12-25% of the total variation in BP response attributable to additive genetic effects. The genetic correlations between baseline DBP and response phenotypes were not significantly different from zero, whereas the genetic correlation between DBP reactivity and recovery (0.74) was significantly different from zero and 1 (P < 0.005). The genetic correlation between SBP reactivity and recovery was similar (0.81; P < 0.05).

CONCLUSION

We conclude that, independent of baseline BP, BP response to CPT is heritable, and that both shared and unshared genetic factors influence BP reactivity and recovery, thus stressing the importance of identifying genetic variants that influence both traits.

The role of functional foods in the psychobiology of health and disease

The effect of psychological stress on health is becoming a serious concern, with figures from the World Health Organization showing that stress-related disorders affect nearly 450 million individuals worldwide. Heightened physiological stress responses and psychosocial factors have been linked to disease pathways such as hypertension and CVD. This has prompted significant interest within the scientific community, public health bodies and industry to employ interventions to control and reduce the impact of stress on health. There is now strong potential for functional foods to offer stress management benefits. Various physiological pathways have been targeted by specific dietary supplements for stress reduction, including the hypothalamic–pituitary–adrenal axis and sympathetic nervous system. Presently there are a number of ingredients, which include vitamin C, milk proteins, a number of herbal extracts (ginkgo biloba, ginseng, kava, valerian and lemon balm), andn-3 fatty acids, that have demonstrated potential stress reactivity-lowering and mood-enhancing effects, although further work is required to substantiate the efficacy in human subjects. Dietary supplements that can alleviate excessive stress responses may play an increasingly important role for the maintenance of health in a stressful environment. However, future research should employ a greater range of measures that will provide stronger evidence to substantiate functional food claims for stress relief.

Effect of acute hyperlipidemia on autonomic and cardiovascular control in humans

Blood lipids may detrimentally affect autonomic and circulatory control. We tested the hypotheses that acute elevations in free fatty acids and triglycerides (acute hyperlipidemia) impair baroreflex control of cardiac period [cardiovagal baroreflex sensitivity (BRS)] and muscle sympathetic nerve activity (MSNA: sympathetic BRS), increase MSNA at rest, and augment physiological responses to exercise. Eighteen young adults were examined in this randomized, double-blinded, and placebo-controlled study. BRS was determined using the modified Oxford technique before (pre) and 60 min (post) after initiating infusion of Intralipid (0.8 ml·m−2·min−1) and heparin (1,000 U/h) (experimental; n = 12) to induce acute hyperlipidemia, or saline (0.8 ml·m−2·min−1) and heparin (1,000 U/h) (control; n = 6). Responses to isometric handgrip to fatigue (IHG) were also determined. Blood pressure increased more ( P < 0.05) in experimental than control subjects during the infusion. MSNA at rest (14 ± 2 vs. 11 ± 1 bursts/min), cardiovagal (19.8 ± 1.8 vs. 19.1 ± 2.4 ms/mmHg pre and post, respectively) and sympathetic BRS (−5.5 ± 0.6 vs. −5.2 ± 0.4 au·beat−1·mmHg−1), and the neural and cardiovascular responses to IHG were unchanged by acute hyperlipidemia (pre vs. post) in experimental subjects. Similarly, MSNA at rest (10 ± 2 vs. 12 ± 2 bursts/min), cardiovagal (22.1 ± 4.0 vs. 21.0 ± 4.6 ms/mmHg) and sympathetic BRS (−5.8 ± 0.5 vs. −5.5 ± 0.5 au·beat−1·mmHg−1), and the neural and cardiovascular responses to IHG were unchanged by the infusion in control subjects. These data do not provide experimental support for the concept that acute hyperlipidemia impairs reflex cardiovagal or sympathetic regulation in humans.

Fish oil induced increase in walking distance, but not ankle brachial pressure index, in peripheral arterial disease is dependent on both body mass index and inflammatory genotype

Peripheral arterial disease (PAD) is an atherosclerotic disease. Evidence suggests that atherosclerosis is an inflammatory condition and long chain n-3 fatty acids, found in oily fish and fish oils, have been shown to reduce inflammation. Genetic and lifestyle factors such as body mass index (BMI) also influence inflammation. In this study we have examined the effect of fish oil in patients with claudication secondary to PAD. Fish oil supplementation, providing 1g EPA and 0.7 g DHA per day for 12 weeks, increased walking distance on a treadmill set at 3.2 km/h with a 7% incline. Walking distance to first pain increased from 76.2+/-8.5 m before fish oil to 140.6+/-25.5 m after fish oil (mean+/-SEM, p=0.004) and total distance walked increased from 160.0+/-21.5 m before fish oil to 242.1+/-34.5 m after fish oil (p=0.002). Fish oil supplementation also improved ankle brachial pressure index (ABPI) from 0.599+/-0.017 before fish oil to 0.776+/-0.030 after fish oil (p<0.001). The increase in walking distance was dependent on both BMI and genotype for single nucleotide polymorphisms in the genes encoding the pro-inflammatory cytokines tumour necrosis factor-alpha and interleukin (IL)-1beta and the anti-inflammatory cytokine IL-10 (detected using amplification refractory mutation system polymerase chain reaction). Neither BMI nor any of the genotypes examined affected the ability of fish oil to increase ABPI. The mechanisms by which fish oil affects walking distance and ABPI do not appear to be the same.

Metabolic effects of parenteral nutrition enriched with n-3 polyunsaturated fatty acids in critically ill patients

BACKGROUND & AIMS

n-3 fatty acids are expected to downregulate the inflammatory responses, and hence may decrease insulin resistance. On the other hand, n-3 fatty acid supplementation has been reported to increase glycemia in type 2 diabetes. We therefore assessed the effect of n-3 fatty acids delivered with parenteral nutrition on glucose metabolism in surgical intensive care patients.

METHODS

Twenty-four surgical intensive care patients were randomized to receive parenteral nutrition providing 1.25 times their fasting energy expenditure, with 0.25 g of either an n-3 fatty acid enriched-or a soy bean-lipid emulsion. Energy metabolism, glucose production, gluconeogenesis and hepatic de novo lipogenesis were evaluated after 4 days.

RESULTS

Total energy expenditure was significantly lower in patients receiving n-3 fatty acids (0.015+/-0.001 vs. 0.019+/-0.001 kcal/kg/min with soy bean lipids (P<0.05)). Glucose oxidation, lipid oxidation, glucose production, gluconeogenesis, hepatic de novo lipogenesis, plasma glucose, insulin and glucagon concentrations did not differ (all P>0.05) in the 2 groups.

CONCLUSIONS

n-3 fatty acids were well tolerated in this group of severely ill patients. They decreased total energy expenditure without adverse metabolic effects.

Supplementation with omega-3 polyunsaturated fatty acids augments brachial artery dilation and blood flow during forearm contraction

Omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have beneficial effects on the heart and vasculature. We tested the hypothesis that 6 weeks of dietary supplementation with DHA (2.0 g/day) and EPA (3.0 g/day) enhances exercise-induced increases in brachial artery diameter and blood flow during rhythmic exercise. In seven healthy subjects, blood pressure, heart rate and brachial artery diameter, blood flow, and conductance were assessed before and during the last 30 s of 90 s of rhythmic handgrip exercise (30% of maximal handgrip tension). Blood pressure (MAP), heart rate (HR), and brachial artery vascular conductance were also determined. This paradigm was also performed in six other healthy subjects who received 6 weeks of placebo (safflower oil). Placebo treatment had no effect on any variable. DHA and EPA supplementation enhanced contraction-induced increases in brachial artery diameter (0.28+/-0.04 vs. 0.14+/-0.03 mm), blood flow (367+/-65 vs. 293+/-55 ml min-1) and conductance (3.86+/-0.71 vs. 2.89+/-0.61 ml min-1 mmHg-1) (P<0.05). MAP and HR were unchanged. Results indicate that treatment with DHA and EPA enhances brachial artery blood flow and conductance during exercise. These findings may have implications for individuals with cardiovascular disease and exercise intolerance (e.g., heart failure).

Effect of Fish Oil on Heart Rate in Humans

Background— The effect of fish oil on heart rate (HR), a major risk factor for sudden death, is not well established. We calculated this effect in a meta-analysis of randomized, double-blind, placebo-controlled trials in humans.

Methods and Results— Randomized trials of fish oil that evaluated HR were identified through MEDLINE (1966 through January 2005), hand-searching of references, and contact with investigators for unpublished results. Two investigators independently extracted trial data. A pooled estimate was calculated from random-effects meta-analysis. Predefined stratified meta-analyses and meta-regression were used to explore potential heterogeneity. Of 197 identified articles, 30 met inclusion criteria. Evidence for publication bias was not present. In the overall pooled estimate, fish oil decreased HR by 1.6 bpm (95% CI, 0.6 to 2.5; P =0.002) compared with placebo. Between-trial heterogeneity was evident (Q test, P <0.001). Fish oil reduced HR by 2.5 bpm ( P <0.001) in trials with baseline HR ≥69 bpm (median) but had little effect (0.04-bpm reduction; P =0.56) in trials with baseline HR <69 bpm ( P for interaction=0.03). Fish oil reduced HR by 2.5 bpm ( P <0.001) in trials with duration ≥12 weeks but had less effect (0.7-bpm reduction; P =0.27) in trials with duration <12 weeks ( P for interaction=0.07). HR reduction with fish oil intake did not significantly vary by fish oil dose (range, 0.81 to 15 g/d), type of HR measure, population age, population health, parallel versus crossover design, type of control oil, or study quality by Delphi criteria ( P for interaction >0.25 for each).

Conclusions— In randomized controlled trials in humans, fish oil reduces HR, particularly in those with higher baseline HR or longer treatment duration. These findings provide firm evidence that fish oil consumption directly or indirectly affects cardiac electrophysiology in humans. Potential mechanisms such as effects on the sinus node, ventricular efficiency, or autonomic function deserve further investigation.