A rigorous U.S. government-led study found that zinc and folic acid supplements don't boost men’s fertility, despite promotional claims that they do.

The mineral and the vitamin are important for sperm production and are found in many common foods. Previous studies on whether over-the-counter supplements might boost sperm health have had conflicting results.

“There were a few small trials that showed a benefit, but we needed some definitive evidence that this would work,” said lead author Enrique Schisterman, a researcher at the National Institute of Child Health and Human Development. The study published Tuesday in the Journal of the American Medical Association showed it didn’t.

Schisterman called the results disappointing. Supplements cost about $60 a month compared with tens of thousands of dollars many couples spend on invasive medical treatment for infertility.

“People who go through fertility treatment are really, really desperate to find something that works,” he said.

The institute paid for the study, which involved almost 2,400 men planning fertility treatments with their partners at four U.S. clinics.

The researchers avoided using over-the-counter supplements, which aren’t strictly regulated and may contain ingredients other than those listed on the label. Instead they created tablets that combined 5 milligrams of folic acid, similar to previous studies, and 30 mgs of zinc, a lower dose than in some studies to avoid potential side effects.

Half the men studied swallowed one tablet daily for six months; the other men took dummy pills. Several semen tests were performed during the study.

Over 18 months of follow-up, 820 babies were born, about equal numbers in each group. Sperm quality also was similar in both groups.

Sperm DNA changes linked with infertility were slightly more common in the supplement users and those men had more digestive side effects, which have been linked previously with zinc pills.

Infertility affects 1 in 8 U.S. couples, and at least 50 million couples worldwide. It’s usually defined as not being able to conceive after a year of trying. Male infertility including low sperm counts or poor-quality sperm contributes to about 1 in 3 cases. Research suggests sperm counts in western countries have been declining for decades, for unknown reasons.

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Follow AP Medical Writer Lindsey Tanner at @ LindseyTanner.

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