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Omega-3 Fatty Acids and Cardiovascular Disease: Current State of the Evidence

Author/s: 
Balk, Ethan M., Adam, Gaelen P., Langberg, Valerie, Halladay, Christopher, Chung, Mei, Lin, Lin, Robertson, Sarah, Yip, Agustin, Steele, Dale, Smith, Bryant T., Lau, Joseph, Lichtenstein, Alice H., Trikalinos, Thomas A.

Focus of This Summary

This is a summary of a systematic review that evaluated the recent evidence regarding the effects of omega-3 fatty acids (FAs), primarily from marine oil supplements, on clinical and selected intermediate cardiovascular (CV) outcomes (i.e., blood pressure, lipid concentrations) and the association of omega-3 FA dietary intake and biomarkers with CV outcomes. The systematic review included 147 articles published between 2000 and June 2015. Studies that analyzed levels of fish (or other food) consumption without exact quantification of omega-3 FA intake were excluded from this review. This summary is provided to assist in informed clinical decisionmaking. However, reviews of evidence should not be construed to represent clinical recommendations or guidelines.

Background

The first observation of a link between fish consumption and cardiovascular (CV) health was made in the late 1970s in a Greenland Eskimo population. This population exhibited a comparatively low rate of CV mortality and consumed a greater than average amount of fish. Since this original observation, there have been hundreds of studies conducted to evaluate the effect of omega-3 fatty acids (FAs) on cardiovascular disease (CVD), its risk factors, and its biomarkers.

The omega-3 FAs include eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), and alpha-linolenic acid (ALA). These are essential long-chain and very-long-chain polyunsaturated fatty acids that have many physiological effects, including inflammation regulation. EPA, DHA, and DPA are found in fish and other seafood (called dietary marine oils), as well as in supplements prepared from these foods (referred to here as marine oil supplements). ALA is found in walnuts, leafy green vegetables, and oils such as canola, soy, and flaxseed.

An original systematic review of omega-3 FAs was prepared by the Agency for Healthcare and Research Quality in 2004.1,2 Based on the observational studies available at that time, several expert panels suggested that regular consumption of fish and seafood is associated with lower risk of coronary heart disease (CHD) and cardiac death. The recommendations were based on assumptions of benefits from EPA and DHA and their content in fish and seafood.

The current systematic review aimed to update the evidence in light of the more recent literature published on the topic and included both randomized controlled trials (RCTs) and observational studies. Studies that analyzed levels of fish (or other food) consumption without exact quantification of omega-3 FA intake were excluded.

Conclusions

Observational studies suggest possible benefits of dietary intake of marine oils (such as through consumption of fish) for CV death and total stroke (mainly ischemic stroke).

In contrast, there is high strength of evidence (SOE) from RCTs that marine oil supplements do not affect the risk of major adverse cardiac events (MACE), all-cause death, sudden cardiac death, revascularization, or high blood pressure (BP). Marine oil supplements also have no effect on the risk of atrial fibrillation (moderate SOE). Importantly, RCTs focused primarily on marine oil supplements, not on food sources.

Marine oil supplements affect several intermediate outcomes. First, they significantly lower triglycerides (TGs)—possibly having greater effects in higher doses and in people with higher baseline TGs. Second, they cause small increases in both high-density lipoprotein cholesterol (HDL-c) and low-density lipoprotein cholesterol (LDL-c). Finally, marine oil supplements produce small changes in the ratio of total cholesterol to HDL-c (high SOE).

Keywords 
omega-3 fatty acids cholesterol blood pressure

Efficacy and safety of statin therapy in older people: a meta-analysis of individual participant data from 28 randomised controlled trials

Author/s: 
Cholesterol Treatment Trialists' Collaboration

BACKGROUND:

Statin therapy has been shown to reduce major vascular events and vascular mortality in a wide range of individuals, but there is uncertainty about its efficacy and safetyamong older people. We undertook a meta-analysis of data from all large statin trials to compare the effects of statin therapy at different ages.

METHODS:

In this meta-analysis, randomised trials of statin therapy were eligible if they aimed to recruit at least 1000 participants with a scheduled treatment duration of at least 2 years. We analysed individual participant data from 22 trials (n=134 537) and detailed summary data from one trial (n=12 705) of statin therapy versus control, plus individual participant data from five trials of more intensive versus less intensive statin therapy (n=39 612). We subdivided participants into six age groups (55 years or younger, 56-60 years, 61-65 years, 66-70 years, 71-75 years, and older than 75 years). We estimated effects on major vascular events (ie, major coronary events, strokes, and coronary revascularisations), cause-specific mortality, and cancer incidence as the rate ratio (RR) per 1·0 mmol/L reduction in LDL cholesterol. We compared proportional risk reductions in different age subgroups by use of standard χ2 tests for heterogeneity when there were two groups, or trend when there were more than two groups.

FINDINGS:

14 483 (8%) of 186 854 participants in the 28 trials were older than 75 years at randomisation, and the median follow-up duration was 4·9 years. Overall, statin therapy or a more intensive statin regimen produced a 21% (RR 0·79, 95% CI 0·77-0·81) proportional reduction in major vascular events per 1·0 mmol/L reduction in LDL cholesterol. We observed a significant reduction in major vascular events in all age groups. Although proportional reductions in major vascular events diminished slightly with age, this trend was not statistically significant (ptrend=0·06). Overall, statin or more intensive therapy yielded a 24% (RR 0·76, 95% CI 0·73-0·79) proportional reduction in major coronary events per 1·0 mmol/L reduction in LDL cholesterol, and with increasing age, we observed a trend towards smaller proportional risk reductions in major coronary events (ptrend=0·009). We observed a 25% (RR 0·75, 95% CI 0·73-0·78) proportional reduction in the risk of coronary revascularisation procedures with statin therapy or a more intensive statin regimen per 1·0 mmol/L lower LDL cholesterol, which did not differ significantly across age groups (ptrend=0·6). Similarly, the proportional reductions in stroke of any type (RR 0·84, 95% CI 0·80-0·89) did not differ significantly across age groups (ptrend=0·7). After exclusion of four trials which enrolled only patients with heart failure or undergoing renal dialysis (among whom statin therapy has not been shown to be effective), the trend to smaller proportional risk reductions with increasing age persisted for major coronary events (ptrend=0·01), and remained non-significant for major vascular events (ptrend=0·3). The proportional reduction in major vascular events was similar, irrespective of age, among patients with pre-existing vascular disease (ptrend=0·2), but appeared smaller among older than among younger individuals not known to have vascular disease (ptrend=0·05). We found a 12% (RR 0·88, 95% CI 0·85-0·91) proportional reduction in vascular mortality per 1·0 mmol/L reduction in LDL cholesterol, with a trend towards smaller proportional reductions with older age (ptrend=0·004), but this trend did not persist after exclusion of the heart failure or dialysis trials (ptrend=0·2). Statin therapy had no effect at any age on non-vascular mortality, cancer death, or cancer incidence.

INTERPRETATION:

Statin therapy produces significant reductions in major vascular events irrespective of age, but there is less direct evidence of benefit among patients older than 75 years who do not already have evidence of occlusive vascular disease. This limitation is now being addressed by further trials.

FUNDING:

Australian National Health and Medical Research Council, National Institute for Health Research Oxford Biomedical Research Centre, UK Medical Research Council, and British Heart Foundation.

Keywords 
statin statin therapy cholesterol, LDL
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