October 24/London/Reuters -- Young men who eat more than three slices of cheese a day may be risking their chances of becoming fathers, a new Harvard study has claimed.

Researchers discovered that even small amounts of full-fat dairy food can dramatically impair fertility in men. They found that men who eat even three portions of cheese a day had poorer quality sperm compared to others, the Daily Mail reported.

A portion includes 28g of cheese, a teaspoon of cream, a scoop of ice cream or glass of full-fat milk.

Researchers believe that female hormones that occur naturally in milk may be interfering with men’s ability to reproduce.

Scientists from the Harvard School of Public Health in the U.S. compared the diets of 189 men aged 19 to 25, all very fit and did at least one and a half hour’s exercise a week. They filled in a questionnaire, answering how often they ate dairy products, fruit, meat and other types of food during a typical week. Researchers also looked at their sperm quality, including how fast it travelled and its shape.

They found that the sperm of men who ate more than three portions of full-fat dairy food a day was of 25% poorer quality than those who had less.

Myriam Afeiche, who led the study, explained that the female hormone oestrogen in milk that had come from the cow may be affecting men’s fertility.

It may be impaired by pesticides which find their way in to dairy products, she added.

However, Dr Allan Pacey, fertility expert at the University of Sheffield and Chairman of the British Fertility Society said men should not give up on dairy purely on the basis of this study.

He pointed out that even though the men’s fertility had gone down, they wouldn’t have any problems conceiving.

“Although it goes down, it doesn’t go into the red. A change of that magnitude for a man in a fertility clinic, we wouldn’t worry about that,” Pacey said.