Young men eating just three slices of cheese a day could be putting their fertility at risk, scientists say.

Harvard University researchers examined the diets of 169 fit men, aged between 19 and 25. They all did at least an hour-and-a-half of exercise each day. They answered questions about how often they ate fruit, veges, dairy and other products. They also had their sperm checked to take note of the shape and how fast they swam.

The men who ate more than three servings of full-fat dairy a day had a 25 per cent decrease in sperm quality, they found. A portion included 28 grams of cheese, a teaspoon of cream, a scoop of ice cream, or a 250ml glass of full-fat milk.

Myriam Afeiche, who led the study, said the female hormone estrogen from cows, which naturally ends up in milk, could be to blame. Pesticides, chlorinated pollutants and heavy metals could also be to blame, she said.


While a man's fertility is affected by dairy, it's unlikely they won't be able to conceive, Afeiche said.

The paper will be presented at a conference in San Diego.