Therapeutic Effect of EPA and DHA Supplementation in Neoplastic and Non-Neoplastic Companion Animal Diseases

Magalhães, T. R., Lourenço, A. L., Gregório, H., & Queiroga, F. L. (2021). Therapeutic Effect of EPA and DHA Supplementation in Neoplastic and Non-Neoplastic Companion Animal Diseases: A Systematic Review. In Vivo, 35(2), 1419–1436. https://doi.org/10.21873/invivo.12394

Study Objectives

The review set out to evaluate whether dietary supplementation with EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) improved clinical outcomes in companion animals diagnosed with either:

• Neoplastic diseases (cancerous conditions), or
• Non-neoplastic diseases (such as dermatitis, arthritis, dry eye, or heart failure).

What the Authors Did

• Searched for randomized controlled trials (RCTs) published up to 2020
• Included 23 RCTs (20 in dogs, 3 in cats)
• Reviewed data on:
  • Study design and quality
  • EPA/DHA dose and source
  • Target condition and response to treatment

Note: This was a systematic review, not a meta-analysis—so data were summarized qualitatively, not statistically pooled.

Who Was Studied?

• 978 dogs and 68 cats
• Conditions included:
  • Neoplastic: lymphoma, mammary tumors
  • Non-neoplastic: allergic dermatitis, osteoarthritis, dry eye (KCS), periodontal disease, heart failure

What They Found: Key Takeaways

1. EPA and DHA Show Consistent Therapeutic Effects—Mostly in Dogs

• The most consistent benefits were seen in:
  • Inflammatory skin conditions (e.g., allergic dermatitis)
  • Joint disease (osteoarthritis)
  • Cardiac conditions (chronic heart failure)
  • Some cancers (lymphoma: longer survival in one study)

2. Primary Mechanisms Involve Inflammation Control

EPA and DHA work by:

• Downregulating pro-inflammatory cytokines (e.g., TNF-α, IL-1β, IL-6)
• Inhibiting MMPs and COX-2—enzymes involved in tissue breakdown and pain
• Altering cell membrane phospholipid composition, which changes inflammatory signaling
• Competing with arachidonic acid, reducing the production of pro-inflammatory prostaglandins and leukotrienes

3. Effects Were Dose-Dependent—but Not Always Linearly So

• Doses varied widely, from 50 mg/kg/day to 310 mg/kg/day
• Some studies showed benefits at lower doses; others required higher concentrations
• Clinical effects likely depend on baseline inflammation, disease severity, and formulation bioavailability

4. Feline Research Is Lacking

• Only 3 RCTs in cats were included
• While trends were positive (especially for OA and dermatitis), sample sizes were small, and effects less consistent

Limitations of the Evidence

• Heterogeneity: Studies varied in dosing, duration, disease type, and outcome measures
• Lack of standardization in omega-3 sources (some used fish oil blends; others used purified compounds)
• Few long-term studies
• More feline-specific trials are needed

Clinical Significance

• For dogs, EPA and DHA supplementation is supported as a low-risk, biologically plausible adjunct in managing chronic inflammatory diseases
• For cancer, evidence is promising but limited—potential role in tumor progression and cachexia mitigation
• For heart disease, one study showed extended survival in dogs with DCM when given fish oil
• In dermatology and orthopedic cases, these fatty acids can reduce medication reliance (e.g., steroids or NSAIDs)