# Dietary vitamin E: effect on oxidative stress, maze learning performance, and anxiety behaviors in rats

## TL;DR

This study shows that higher dietary vitamin E in rats reduces anxiety but increases oxidative stress, suggesting there's a limit to its benefits.

## Contribution

The study reveals that high vitamin E intake reduces anxiety behaviors but correlates with increased oxidative stress in rats.

## Key findings

- Higher vitamin E concentrations reduced anxious behaviors but increased oxidative stress markers.
- Rats with 20 ppm vitamin E showed more freezing and grooming behaviors, indicating higher anxiety.
- Working memory errors increased with higher serum TBARS concentrations.

## Abstract

The brain is particularly susceptible to oxidative stress (OS) and damage to membranes is associated with learning and memory decline, impacting animal welfare. Vitamin E is an antioxidant which crosses the blood-brain barrier. Our objectives were to assess the impact of dietary vitamin E concentrations (20, 90, and 400-ppm) on markers of OS, maze learning performance (MLP), and anxious behaviors in 3-wk old Long-Evans rats. Vitamin E concentrations, antioxidant enzymes (superoxide dismutase [SOD] and glutathione peroxidase [GPx]), and oxidative protein damage (protein carbonyls [PC]) were measured in plasma or serum. Lipid damage (thiobarbituric acid reactive substances [TBARS]) was measured in serum and hippocampus. Anxious behaviors, including freezing and grooming, and MLP were assessed in an eight-arm radial maze over 5 weeks. Activity of SOD was lower (P = 0.002), and PC concentrations were higher (P = 0.022) in the 400-ppm group (1.0 U/mL; 0.7 nmol/mg) compared to the 20 (2.9 U/mL; 0.5 nmol/mg) and 90 (1.7 U/mL; 0.5 nmol/mg). Plasma vitamin E increased (P < 0.050) with dietary treatment and SOD decreased as plasma vitamin E increased (R2 = 0.46; P = 0.002) but PC (R2 = 0.16; P = 0.090) concentrations tended to increase with plasma vitamin E. Dietary treatment did not impact (P > 0.050) maze learning performance. Rats fed 20 ppm vitamin E exhibited greater freezing frequency and duration (P < 0.001) compared to other treatment groups, indicating heightened anxiety. The 400-ppm group exhibited lowest grooming frequency and duration (P < 0.001), possibly indicating less anxiousness. Working memory errors increased with serum TBARS concentrations (R2 = 0.26; P = 0.033). In conclusion, higher dietary vitamin E concentrations reduced anxious behaviors, but did not alter MLP and was correlated with increased OS. These results suggest high concentrations of dietary vitamin E are not beneficial for rat welfare.

More of a good thing is always better, right? Not necessarily. This work shows there might be a limit to the benefits of dietary antioxidants.