Reproductive function in young Swedish men - Time trend, prenatal and adult exposure to smoking and phthalates

Abstract: A decrease in male reproductive function, including sperm counts, during the second half of the 20th century, has been postulated. During this period, testicular cancer has increased several-fold. Environmental and lifestyle-related factors have been proposed as explanations for a possible negative trend in male reproductive function. One important lifestyle factor is smoking. However, smoking during pregnancy appears to play a greater role for a man's reproductive function than smoking by the man himself. As regards environmental chemicals, one type of compound to which humans are exposed is phthalates. These are often used as plasticizers in different consumer products. Several phthalates have been reported as decreasing male reproductive function in laboratory animals, especially when given during the foetal period. Between 2008 and 2010, 314 men from the general Swedish population were recruited. Their semen quality was compared with a group of men recruited in a similar manner between 2000 and 2001. The participants also delivered serum and urinary samples and answered questionnaires concerning maternal and paternal smoking during pregnancy. Data on maternal smoking was additionally assessed through the Swedish Medical Birth Register. Through a Swedish screening program for rubella, maternal serum samples were retrieved from the men's prenatal period. We analysed metabolites of phthalates as exposure markers both in the maternal sera and in urine and serum of the men. Associations between parental smoking during pregnancy as well as phthalate metabolite levels, and parameters of male reproductive function were studied. In summary, we found no change in semen quality between 2000-2001 and 2008-2010. However, both maternal and paternal smoking during pregnancy were associated with reduced sperm counts in men whose other parent did not smoke. In addition, prenatal exposure to diethylhexyl phthalate (DEHP) and diisononyl phthalate (DiNP) appeared to be associated with decreased semen volume, and exposure to DiNP as well with smaller testicular size. Finally, adult exposure to DEHP and dibutyl phthalate (DBP) were associated with decreased progressive sperm motility, and DEHP exposure was also linked to a higher proportion of immature sperm. Thus, although no change in semen quality appeared to have occurred in Swedish men during the last decade, parental smoking and prenatal and adult exposure to certain phthalates may play a role in the male reproductive function.