Vitamin E and polyphenols: Are we comparing apples with apples?

In brief:

Over the past decade, grape seed extracts and other plant-derived polyphenols have been presented as partial alternatives to vitamin E in animal feed. This proposition is based on claims that certain polyphenols, particularly water-soluble flavonoids, possess anti-inflammatory, anti-carcinogenic, and antioxidant properties. Given that vitamin E is an established biological antioxidant, the idea of replacing part of its inclusion in feed with polyphenols can appear appealing—particularly when vitamin E prices are elevated. However, closer examination reveals that such substitutions warrant caution.

Polyphenols in animal nutrition: a complex profile

Polyphenols are not a single compound, but rather a chemically diverse group of over 6,500 distinct molecules found in a variety of plants, including grapes, berries, soy, and brassicas. While some polyphenols have been associated with health benefits in humans—most famously the link between wine polyphenols and reduced cardiovascular disease—their effects in animals are less clearly established.

Research has shown that certain polyphenols may improve immunity and meat quality in livestock. However, not all polyphenols are beneficial. Some high-molecular-weight polyphenols can exert anti-nutritional effects, inhibiting digestive enzymes and reducing growth performance. Others exhibit pro-oxidative activity, potentially impairing protein and fat digestion.

The heterogeneity of polyphenols means that their biological effects cannot be generalized, and the assumption that they can directly substitute for vitamin E requires robust scientific validation

Antioxidant claims: in vitro versus in vivo

A critical point of contention is the evidence supporting polyphenols as biological antioxidants. In 2013, Dr P. Surai concluded that such claims were not sufficiently substantiated, particularly when based on in vitro assays. Many polyphenols that display antioxidant activity in laboratory conditions are metabolized in the gastrointestinal tract into forms that no longer possess the same activity.

Furthermore, polyphenols generally exhibit poor intestinal absorption, with bioavailability often ranging between 10 % and 50 %. This low uptake results in minimal concentrations in target tissues—making it difficult to demonstrate any meaningful antioxidant effect in vivo.

In contrast, vitamin E is efficiently absorbed, readily detected in tissues, and its antioxidant role is well established through decades of research.

Regulatory status and EFSA assessment

In the European Union, the majority of polyphenol-containing feed additives—such as grape seed extracts—are registered solely as sensory additives (flavorings), not as nutritional antioxidants. A notable case occurred in 2023, when an application was submitted to the European Food Safety Authority (EFSA) to register a grape seed extract as a zootechnical additive for poultry, specifically under the functional group “physiological condition stabilizers” with the intended effect of stimulating antioxidant activity.

While EFSA found no major safety concerns, stability issues were observed, with activity losses exceeding 20 % in some premixes after six months of storage. More importantly, EFSA concluded that the provided evidence was insufficient to confirm any in vivo antioxidant effect in broiler chickens or laying hens. Consequently, grape seed extract remains authorized only as a sensory additive in the EU.

 EFSA 2023 Assessment: Grape Seed Extract for Poultry
Additive Type: Proposed as a zootechnical additive – functional group physiological condition stabilisers (antioxidant activity).
Species: All poultry.
Key Findings:

• Safety: No major concerns for poultry identified.
• Stability: Loss of activity >20 % in certain premixes after 6 months’ storage.
• Efficacy: Insufficient in vivo evidence to demonstrate antioxidant effect in broilers or layers.
• Regulatory Outcome: Not approved as a zootechnical additive; remains authorised only as a sensory additive in the EU.

The question of ‘Vitamin E equivalence’

Despite the lack of regulatory recognition, some commercial polyphenol-based products are marketed as providing “vitamin E equivalence.” This practice raises both legal and practical issues:

• Regulatory non-compliance: In the absence of EU registration as a nutritional or zootechnical additive, polyphenol products cannot legally be marketed as replacements for vitamin E.
• Analytical challenges: Polyphenols are difficult to quantify reliably in premixes and final feeds, complicating quality control.
• Stability concerns: Polyphenols can degrade during storage or thermal processing, making consistent efficacy difficult to guarantee.

In practice, these limitations mean that declaring vitamin E equivalence on feed labels is both scientifically unfounded and legally questionable.

Economic and practical implications

While the motivation to reduce feed costs is understandable—especially during periods of high vitamin E prices—the potential risks of partial substitution with unproven alternatives can be significant. Reduced antioxidant protection could impair animal health, performance, and product quality, leading to financial losses far exceeding the short-term savings.

Conclusion

Polyphenols are a chemically diverse group of compounds with potential benefits in animal nutrition, but their role as biological antioxidants in vivo remains unproven for most applications. Regulatory frameworks in the EU currently recognize them primarily as flavorings, not as nutritional antioxidants, and EFSA’s most recent assessment underscores the difficulty of securing such recognition.

Until conclusive, reproducible evidence is available—supported by stable formulations and reliable analytical methods—vitamin E should not be replaced based on assumed equivalence. In feed formulation, scientific rigor and regulatory compliance remain the best safeguards against compromising animal health and production outcomes.