Diabetes is a major public health problem that is approaching epidemic proportions. The International Diabetes Federation predicts that the number of people living with diabetes worldwide will near 643 million by 2030 and 783 million by 2045.
Persistently high blood sugar (glucose) levels can lead to a variety of severe health complications and increase the risk for hypertension, dyslipidemia, and various cardiovascular problems. Moreover, evidence indicates that those with diabetes and prediabetes have a two-fold higher risk of developing coronary heart disease (CHD).
This risk can be very alarming for those affected, but researchers have been investigating a natural solution that may attenuate the growing number of cardiovascular complications in the diabetic population. This article will explore the current literature explaining how increasing omega-3s in the diet may provide cardioprotective benefits for diabetics.
What Is Diabetes?
Diabetes is a chronic health condition that affects how our body turns food into energy. After consuming carbohydrate-rich foods, our bodies break that food down into glucose, which enters our bloodstream. The cells of our body use glucose to produce energy and the hormone insulin is required to ferry glucose from the blood into the cells to be utilized. With diabetes, the cells stop responding to insulin, or the body does not make enough insulin to move glucose into our cells. Either way, the result is elevated sugar levels in the bloodstream, which, over time, can lead to serious health complications.
Prediabetes, on the other hand, is a condition in which blood sugar levels are higher than normal but not high enough yet to be diagnosed as type 2 diabetes. Nonetheless, a person with prediabetes still has an elevated risk for serious health conditions, and studies show that those with prediabetes can experience increased risk of CHD without progression to diabetes. Since heart disease is a significant concern for individuals with diabetes and prediabetes, researchers have conducted studies to investigate solutions to minimize that risk.
Omega-3s and Cardiovascular Health
Marine-derived omega-3 supplements are widely consumed because of the many health benefits associated with their bioactive components, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Several studies have explored the relationship between DHA and EPA intake and the risk of CHD and other cardiovascular outcomes.
A 2021 systematic review and meta-analysis of 38 trials comprising over 149,000 adult participants noted that omega-3 fatty acids reduced cardiovascular mortality and other cardiovascular outcomes. Moreover, using the Omega-3 Index, the percentage of EPA + DHA (of total fatty acids) measured in the erythrocytes has become the norm when considering cardiovascular risk.
BLOG: Does Fish Oil Prevent Blood Clots?
The Omega-3 Index has been determined to be a valid representation of an individual’s EPA + DHA status compared to omega-3 intake, which is difficult to rely on based on the complex and varying bioavailability of dietary EPA + DHA. Evidence indicates that an ideal Omega-3 Index range of 8-11% is associated with beneficial effects on total mortality, major adverse cardiovascular events, and other cardiovascular issues.
The cardioprotective effects of DHA and EPA, as explained in the literature, are due to the modulation of several known risk factors for cardiovascular disease (CVD). The primary mechanism through which omega-3s influence cardiovascular outcomes is the inhibition of downstream inflammatory processes.
Through several actions, such as decreasing pro-inflammatory cytokines like CRP and IL-6, and the promotion of specialized pro-resolving mediators (SPMs), omega-3s play a vital role in anti-inflammatory processes. Moreover, omega-3s also affect lipid modulation and have been found to decrease serum triglycerides, LDL-C oxidation, and hepatic lipogenesis, improving blood lipid profiles. Meta-analyses demonstrate that EPA and DHA can lower triglycerides, lower blood pressure, reduce heart rate and heart rate variability, and reduce platelet aggregation. A more detailed explanation of omega-3 mechanisms of action can be found in a 2023 review by Bhat et al.
Omega-3s Offer Cardiovascular Benefits for Diabetics
While most evidence uses large populations of mixed health standing, more research is beginning to focus on the diabetic population. A 2019 study that included over 11,000 participants from the Nurses’ Health Study and the Health Professionals Follow-Up Study concluded that the consumption of marine omega-3 fatty acids was associated with lower total mortality and CVD mortality in patients with type 2 diabetes.
A 2020 study set out to quantify the association of plasma fatty acid biomarkers with macrovascular disease, microvascular disease, and death in individuals with type 2 diabetes. They found that, in a population of over 3,500 participants with diabetes, omega-3 fatty acids were inversely associated with macrovascular disease, and inversely associated with death in this population. A 2021 meta-analysis demonstrated that each additional serving of fish per week was related to an 8% lower risk of CHD (but not myocardial infarction or stroke) in patients with diabetes.
BLOG: Blood Sugar and Heart Health
Although we know more now than ever about the effects of omega-3s on cardiovascular health in diabetic populations, most of the evidence focuses on relationships between omega-3 intake and poor outcomes or mortality associated with CVD. But what if we can get ahead of the curve and focus on prevention?
CHD is the most common CVD among patients with diabetes. Yet, few studies to date have assessed the effects of dietary consumption of omega-3s on CHD risk in this population until now. A brand-new study set out to determine the association between long-term fish oil use and CHD prevention among adults with diabetes and prediabetes.
New Evidence Points to Significant Effects of Omega-3s on CHD Outcomes in Diabetic Populations
Published in July 2023, this prospective study utilized the UK Biobank to investigate the enduring association between habitual fish oil supplementation and CHD risk among 47,663 participants with prediabetes and 22,146 participants with diabetes. Of the participants with prediabetes and diabetes, 15,936 and 6,310 were found to consume fish oil supplements, respectively.
After an approximately 10-year follow-up, the authors found that fish oil supplements were significantly linked with a 9% and 13% lower incidence of CHD in participants with diabetes and prediabetes independent of various confounding factors.
BLOG: 5 Nutrients that Keep Your Heart Healthy
The authors determined the positive associations were mainly mediated by CRP in participants with prediabetes and VLDL-C in patients with diabetes. The mechanism to explain the inverse association between omega-3s and CRP levels was ascribed to omega-3s anti-inflammatory properties. In individuals with diabetes, fish oil supplementation appeared to benefit VLDL-C levels, which can lower the risk for adverse CVD outcomes. These results provide evidence, possibly for the first time, supporting using marine-derived omega-3s for the primary prevention of CHD in the diabetic patient population.
Mixed Outcomes Explained
Data from large-scale trials on omega-3s and cardiovascular health has been mixed. Yet, when assessing study outcomes, researchers urge us to consider possible explanations for different conclusions.
First, it’s always important to consider dosing. Several meta-analyses have identified a dose-response correlation between marine omega-3 intake and CVD risk. For example, the ORIGIN and ASCEND trials, which used only 1g of EPA + DHA daily over time did not decrease the risk of CVD death or other CVD cases in patients with impaired fasting glucose or diabetes. Yet, the REDUCE-IT study, which used 4g per day of EPA, observed reduced CVD events and death in a subgroup analyses of over 4,500 diabetes patients. Likewise, these positive results were similar in another trial using 1.8g/d EPA supplementation over 4.6 years. The bottom line is, low doses of omega-3s may not be beneficial in reducing CVD, and higher dosages may be required.
BLOG: What is the Normal Blood Sugar by Age?
Furthermore, the authors highlight the choice of placebos used when assessing study outcomes. For example, many studies chose olive oil as a placebo, and olive oil itself has anti-platelet and anti-inflammatory properties, which might obscure the effectiveness of omega-3 supplementation. These considerations might help explain some of the discrepancies in study outcomes.
Conclusion
A large body of evidence consistently demonstrates an association between higher intakes of fish or higher levels of marine-derived omega-3s, particularly EPA, and a lower risk of developing CVD, especially CHD, in the general population. While studies on diabetic populations are less numerous, several studies have demonstrated similar beneficial effects of omega-3s on cardiovascular risk in this population.
Again, very recent evidence confirms this theory by demonstrating that regular intake of fish oil supplementation is significantly related to a reduced risk of CHD in participants with diabetes and prediabetes. The relationship appears to be mediated through serum CRP in individuals with prediabetes and VLDL-C in those with diabetes at baseline.
Effects might be dose-dependent and focusing on omega-3 status rather than intake may provide a clearer picture of the relevance, effect, and safety of EPA + DHA when used as a clinical prevention or intervention tool. While additional studies are required to explore optimal dosage and duration, current evidence supports using omega-3 fatty acids as the primary prevention of CHD in those with diabetes or prediabetes.
