Taking zinc or folic acid supplements does not boost male fertility, according to a new study.
Researchers found consuming those dietary supplements on a daily basis did not improve the semen quality of men seeking infertility treatment.
The scientists in the US recruited 2,370 couples as part of The Folic Acid and Zinc Supplementation Trial.
As it was a double-blind randomised trial, neither the researchers nor the volunteers knew who was taking the dietary supplements and who was receiving the placebo.
The men taking part in the trial were aged 18 years and above while the women were between 18 and 45 years old.
Half of the men in the group were given 5mg of folic acid and 30mg of zinc to consume daily for six months while the other half received a placebo.
All the couples were receiving treatment at a US infertility centre at the time of the study.
Those planning use of donor sperm or a gestational surrogate or were pregnant at enrolment were not included.
Men with azoospermia, a medical condition where semen contains no sperm, were also excluded from the trial.
Semen samples were collected throughout the study and the quality of the specimens were analysed by examining the shape, size and structure of the sperm as well as sperm concentration and total motile sperm count.
At the end of the trial, 820 couples gave birth.
According to the researchers, live birth “was not significantly different between treatment groups”, with 404 successful births in the folic acid and zinc group compared to 416 in the placebo group.
In addition, the team said they observed “a statistically significant increase in DNA fragmentation” in the samples from the folic acid and zinc group (29.7%) compared to the placebo group (27.2%), indicating “an increased sperm DNA damage associated with supplementation”.
The researchers said their findings contradict previous research, including a meta-analysis published in 2017 in the Urology Journal which suggests folic acid and zinc supplements have a positive effect on sperm quality in sub-fertile men.
Writing in the The Journal of the American Medical Association, the team noted: “Among a general population of couples seeking infertility treatment, the use of folic acid and zinc supplementation by male partners, compared with placebo, did not significantly improve semen quality or couples’ live birth rates.
“These findings do not support the use of folic acid and zinc supplementation by male partners in the treatment of infertility.”
