'There has always been this heavy concern in the past with expectant mums not smoking and not drinking, for example, to protect the fetus,' said lead author Dr Richard Pilsner of the University of Massachusetts Amherst, USA. 'In this study, we see that dad's environmental health contributes to reproductive success.'
Phthalates, used in products ranging from shaving cream to food packaging, are estimated to be detectable in nearly 100 percent of the US population. They have been associated with lower sperm concentration and movement, and increased sperm cell DNA damage and death.
The small study examined the urine of 48 men from couples attending the IVF clinic at Baystate Medical Centre, Massachusetts for eight different phthalate concentrations. They also analysed DNA extracted from sperm, taken on the same day, for epigenetic changes in regions of the genome.
Semen samples from men with higher urinary concentrations of phthalate metabolites were associated with a methylation on 131 regions of sperm DNA. The researchers found many of these regions affected the function of genes related to growth, development and 'basic cellular function', and some were also associated with poorer quality of blastocysts.
Dr Pilsner said: 'For sperm to mature is a 72-day process, almost three months, and our study shows that this preconception time-period may represent an important developmental window by which environmental exposures may influence sperm epigenetics, and in turn, early life development. So in the same way mum needs to be careful, dad also needs to.'
Coming from a small study, the findings need to be replicated and confirmed on a larger scale. Additionally as all of the men were recruited from an IVF clinic, the findings may not apply to the wider population.
Professor Allan Pacey of the University of Sheffield in the UK said the small study should be interpreted with caution, as 'the results only describe an association and not cause and effect'.
'Therefore, men currently undergoing IVF with their partners should not panic as it is very difficult to make any firm conclusions from this data. However, they should concentrate on being as healthy as possible by not smoking cigarettes (a much bigger epigenetic hazard in my view) and eating a sensible diet, with five portions of fruit and vegetables per day (paternal diet has been implicated as important in sperm DNA methylation).'
The study was published in Human Reproduction.