Antioxidants have long been used to treat male infertility as they are thought to reduce oxidative stress on sperm.
A new study has busted myths saying that supplements increase a man's chance of conceiving.
A large clinical trial of 174 couples across eight fertility centers in America - one of the biggest trials to date on supplements and sperm health - saw 'slight' changes after three months, but nowhere near enough to make a difference in fertility.
The findings question the science supporting the booming supplement industry.
All men in the study, led by Professor Anne Steiner from the University of North Carolina at Chapel Hill, had been diagnosed with male factor infertility.
Sperm quality is measured using four main factors.
First: sperm concentration. A 'normal' sperm concentration falls between 15 million and over 200 million sperm per milliliter of semen. A man is diagnosed with a 'low' sperm count if they have fewer than 15 million sperm per milliliter (i.e. less than 39 million sperm per ejaculation).
Second: motility, or the ability for sperm to swim deftly towards the egg. A common cause of infertility is sperm that moves slowly.
Third: morphology, which refers to the size and shape of semen. To be fertile, men need at least four percent of their sperm to be 'normal' shape (with an oval head and a long tail). An 'abnormal' sperm might have a crooked head or a short tail, or even more than one tail, which can make it harder to penetrate the egg.
Lastly, they measured whether the men had a higher amount of DNA fragmentation in their sperm than would be deemed 'normal'.
These sperm parameters were measured at the start of the trial and at three months.
While 'spermatogenesis' (the process of sperm maturing) takes 74 days, the impact of antioxidants is short-term, meaning the effects should be seen very soon after starting the treatment. Three months, they deemed, would be enough to track the impact of these supplements for a few cycles.
The men in the study were each given supplements containing vitamins C, D3 and E, folic acid, zinc, selenium and L-carnitine. The control group received a placebo.
At the end of the trial they found no statistically significant differences.
Crucially, there were no significant differences in sperm concentration, morphology, motility, or DNA fragmentation measurements.
The supplement-taking group had a conception rate of 10.5 percent, compared to 9.1 percent in the placebo.
The team reassessed their fertility rate again at six months - with each person continuing with their supplement or placebo - and the figures didn't budge.