Antioxidants come up frequently in preventive health discussions—for both humans and animals. As horse owners we might feel bombarded with advice about supplementing with antioxidants to support equine health.

Many owners believe sport horses need antioxidant supplements to prevent joint issues. The theory: Antioxidants protect joints under stress, reducing wear and tear from exercise.

But scientific support remains limited. And even if antioxidants reduce equine joint inflammation, that effect might not be as beneficial as it sounds. We spoke with researchers to uncover the latest evidence behind antioxidants and preventive joint health in horses.

What Is an Antioxidant?

Horse owners first need to understand what these molecules are and what they do. “There’s a sense that antioxidants are something like a stress sponge, and that provision of an antioxidant essentially mops up the inflammatory consequences of exercise,” says Wendy Pearson, PhD, associate professor of equine physiology at the University of Guelph, in Ontario, Canada. “This is quite incorrect.”

Antioxidants, as their name implies, counteract oxidants—also called free radicals. The horse’s body naturally produces free radicals during metabolism and immune responses. These molecules also initiate and respond to inflammation, which plays a normal, healthy role in recovery.

Free radicals serve essential purposes, such as cell signaling and immune function, says Seung Jae Lee, PhD, of the Korea Research Institute of Bioscience and Biotechnology, in Daejeon. But when free radicals accumulate in excess, oxidative stress occurs. That imbalance can damage DNA, proteins, and fats, and it contributes to joint degeneration.

The horse’s body produces antioxidants to help regulate this system. Horses also get them from plants, fruits, and vegetables, says Lee. Still, some horses might need additional antioxidants via dietary supplements.

Antioxidants and Equine Joint Health Research

Giving horses supplements to neutralize free radicals might sound smart, but owners should carefully review the research behind supplements before feeding them.

For her dissertation completed at the University of Veterinary Medicine, Budapest, in Hungary, Tamara Abela, DVM, reviewed the literature on 321 commercial oral joint supplements for horses containing 344 active ingredients—many of them antioxidants. Only three ingredients demonstrated antioxidant effects in horses:

• Vitamin C lowered oxidative stress in Standardbred trotters at a 250-milligram dose but not at 125 mg.
• Methylsulfonylmethane (MSM) didn’t improve gait in senior horses but showed antioxidant effects in healthy jumpers. Combining MSM with vitamin C yielded better results than MSM alone.
• Resveratrol reduced lameness in horses with hock pain and improved some oxidative biomarkers in senior and lame horses.

Researchers on these studies used small sample sizes and focused more on treating existing lameness than preventing it; therefore, we need more research, says Pearson.

At the University of Guelph, Pearson’s student Nadia Golestani, a PhD candidate, evaluated the effects of a spirulina-based supplement on healthy horses’ joints. Spirulina contains proteins, amino acids, vitamins, minerals, and potential antioxidants C-phycocyanin and beta carotene.

Golestani measured horses’ blood plasma and synovial fluid biomarkers before and after exercise. Spirulina-fed horses experienced a greater post-exercise drop in nitric oxide—a free radical—compared to controls. Other biomarkers pointed to reduced joint inflammation.

Still, Pearson questions whether spirulina’s antioxidant content alone caused the change. “There is evidence that some antioxidant feed ingredients can play a key role in maintaining cartilage health during and/or following exercise,” she explains. “But these effects are not likely attributed entirely to their antioxidant capacity.” She adds that researchers still need to clarify spirulina’s potential benefits.

Using Antioxidants Appropriately

Exercise triggers temporary inflammation in joints—a normal part of tissue adaptation and healing. “Transient inflammation is good, and it’s needed for recovery,” Pearson says. “Inflammation challenges the tissue, and the tissue responds by becoming stronger.”

Neutralizing free radicals too aggressively could interrupt that process, she adds. Because free radicals help drive inflammation, antioxidants might interfere with healthy adaptation if overused.

However, when inflammation becomes chronic and sustained, it can damage joints and lead to diseases such as osteoarthritis; therefore, striking a balance becomes essential. “We’d like to do something about the way tissue responds to an exercise bout, without interfering with transient inflammation,” Pearson says. “What we want is resolution of inflammation, not prevention of it.”

Take-Home Message

Horses rely on their own antioxidant systems to manage oxidative stress and maintain joint health. Researchers are working to better understand how antioxidants might benefit equine joint health, especially when exercise stresses the joint.