These were consistent with improvements found in other recent studies with diets rich in omega-3, antioxidants (e.g., vitamin C and E, selenium and zinc) and folate.
Dr. Salas-Huetos presented the research at the 34th Annual Meeting of ESHRE.
The decline has been attributed in industrialised countries to "pollution, smoking, and trends toward a western-style diet". One of the groups was given a usual western style diet along with 60 grams per day of mixed nuts (almonds, hazel nuts and walnuts) and the other group ate regular western style diet without the nuts. About 40 to 50 percent of infertility cases are due to infertility among men.
The researchers, from the University Rovira i Virgil, Tarragona, Spain, analysed 119 healthy men aged between 18 and 35 for 14 weeks.
The men who ate nuts saw a 16 percent spike in their sperm count on average, as well as improvements in the overall health of the reproductive cells. Indeed, it was this change in the level of DNA fragmentation in the sperm cells that the investigators explained, at least in part, the improvement in sperm count, motility and morphology.
In the study, subjects randomised to the nut group had significant improvements in their sperm count, vitality, motility and morphology (shape), researchers said. Sperm as well as blood samples were tested for the participants.
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Drawbacks to the study include that all the men were healthy, apparently fertile and eating a specific diet, Dr. Sala-Huetos noted, and that results should not be applied to the total population.
Results further suggest a handful of nuts a day reduces sperm's DNA damage, which can cause male infertility.
Sperm counts have halved in the western world over the past four decades, which, alongside rising testicular tumours, could be behind plummeting fertility rates and couples' increasing dependency on IVF, according to Professor Niels Skakkebaek from the University of Copenhagen.
"We can't yet say that based exclusively on the results of this study", said Dr. Salas-Huetos. "They can adopt healthier nutrition and overall lifestyles that should also have an impact on sperm quality".
"But evidence is accumulating in the literature that healthy lifestyle changes such as following a healthy dietary pattern might help conception", the doctor added, "and of course, nuts are a key component of a Mediterranean healthy diet".