Antioxidants are often promoted as powerful supplements, credited with helping prevent chronic illnesses and cancer, treating conditions like COPD and dementia, and even slowing the aging process.
However, new research from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) suggests that taking high doses regularly may come with unexpected downsides. The study found that excessive antioxidant intake can alter sperm DNA and may increase the likelihood of developmental differences in offspring, particularly in facial and skull formation.
In research published in Frontiers in Cell and Developmental Biology, a team led by Dr. Michael Golding studied two widely used antioxidants, N-acetyl-L-cysteine (NAC) and selenium (Se), using mouse models.
Male mice that received these antioxidants for six weeks produced offspring with noticeable changes in skull and facial structure. Notably, the fathers themselves showed no visible health issues.
These findings raise concerns about high-dose antioxidant use, especially for men who are planning to have children.
When Antioxidant Intake Becomes Excessive
Compounds like NAC are commonly found in supplements, including multivitamins, and are often taken to reduce oxidative stress, which can result from factors such as heavy alcohol use.
Golding’s lab has long examined how a father’s alcohol consumption can affect offspring. Previous work has linked heavy drinking in males to a range of developmental issues in their children, including craniofacial abnormalities. Building on this, the researchers explored whether adding NAC or Se to the diet could counteract those effects.
“We know alcohol causes oxidative stress and we were looking to push back on it by adding a supplement known to lower oxidative stress,” said Golding, a professor in the VMBS’ Department of Veterinary Physiology and Pharmacology. “When we realized that offspring born to males that had only been given NAC were displaying skull and facial differences, it was a surprise because this molecule is universally thought to be good.
“When we sat down to think it through, we realized that it makes sense — you take a multivitamin to ensure that you’re in balance, but if the thing that you’re taking to ensure you’re in balance is unbalanced (the dose of antioxidants is too high), then you’re not doing a good thing.”
Previous studies have already shown that very high antioxidant intake can have drawbacks. For example, it can reduce the benefits of endurance training and negatively affect athletic performance.
“Sperm health is another performance metric; it’s just not one that we think about in everyday life,” Golding said. “If you’re taking a high dose antioxidant, you could be diminishing your reproductive fitness and part of the journey toward the bad outcome is going to be the effects on the offspring.”
Facial Changes May Reflect Brain Development
One of the more unexpected findings involved female offspring, which showed more pronounced physical differences. These included closer-set eyes and smaller skulls, traits also associated with fetal alcohol syndrome.
“There’s a very commonly accepted truism in pediatric medicine that the face mirrors the brain, because the brain and the face form at the same time,” Golding said. “When your face migrates (during gestation), it’s using cues from your brain to know where to go, and if the two things are not aligned, there’s either a delay or some kind of abnormality in brain development.
“So, if you see abnormalities in the midline of the face, you’re probably going to see midline abnormalities in the brain,” he said. “People with these abnormalities typically have problems with impulse control, neurological conditions like epilepsy, and other developmental issues.”
Researchers note that it is still unclear whether the offspring in this study will experience central nervous system issues. More research is needed to determine any long-term neurological effects.
Why Balance Matters With Supplements
The research highlights a key point about nutrition and supplements. Even beneficial compounds can cause harm when taken in excess, particularly without a clear medical need.
Many people regularly consume high-dose supplements, including those rich in antioxidants. This makes it important to carefully review labels and understand how much of each ingredient is being consumed. NAC, for example, is a common component in multivitamins and is sometimes included at elevated levels.
“The larger message here is that there’s a balance,” Golding said. “Think of yourself as a plant — if you stick your plant out in the sun too long, it’s going to get dehydrated. If you overwater your plant, it gets root rot. But if you have the right balance of sunshine and water, that’s when growth occurs. Health is in that domain.
“If your vitamins are providing 1,000% of the recommended daily amount, you should be cautious,” he said. “If you stick to the 100% range, then you should be OK.”
