U.S. women who eat a lot of beef while pregnant give birth to sons who grow up to have low sperm counts, researchers reported Tuesday.
They believe pesticides, hormones or contaminants in cattle feed may be to blame. Chemicals can build up in the fat of animals that eat contaminated feed or grass, and cattle were and are routinely given hormones to boost their growth.
"In sons of 'high beef consumers' (more than seven beef meals/week), sperm concentration was 24.3 percent lower," the researchers wrote in their report, published in the journal Human Reproduction.
The team at the University of Rochester Medical Center in New York studied data on the partners of 387 pregnant women in five U.S. cities between 2000 and 2005, and on the mothers of the fathers-to-be.
Of the 51 men whose mothers remembered eating the most beef, 18 percent had sperm counts classified by the World Health Organization as sub-fertile.
"The average sperm concentration of the men in our study went down as their mothers' beef intake went up. But this needs to be followed carefully before we can draw any conclusions," said Shanna Swan, who led the team.
Swan said she would like to study infertile men to see whether similar findings might hold for them.
"I was really surprised when we found this. It was a really strong association," Swan said in a telephone interview.
Swan is perhaps best known for controversial findings that male sperm counts are falling in many regions. She has been doing research to find out if environmental hormones may be to blame.
"We know from rodent studies that even tiny amounts of estrogen in utero (while in the womb) can affect sperm count," Swan said.