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Research on environment effects on fertility .. 12



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Research on environment effects on fertility .. 12
Posted 2017

Future perspectives
Environmental and lifestyle factors look set to become increasingly influential on human fertility if increasing trends in obesity, female smoking and sedentation at work/leisure continue. Such factors, coupled with a trend to delay first pregnancies to an older age, are likely to result in an increased incidence of infertility, especially in women. However, as many of these effects are on the foetus during pregnancy, their manifestation may be 'hidden' for several decades. Arguably, all such effects are preventable by changes in diet and lifestyle. Ultimately, all environmental/lifestyle effects on fertility, whether induced in foetal or adult life, result from hormonal changes. Genetic differences (for example SULT1E1 polymorphisms) may predispose some indivi…

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Research on environment effects on fertility .. 11
Posted in 2017


First, both PCBs and a range of environmental polyhalogenated hydrocarbons (PAHs) have been shown to potently suppress activity of the enzyme oestrogen sulphotransferase (SULT1E1), through which oestrogens are inactivated. Suppression of SULT1E1 increases oestrogen bioactivity. Furthermore, in human pregnancy, when oestrogen levels are extraordinarily high, this could alter exposure of the foetus to oestrogens, a change that is established to increase risk of male reproductive disorders and function, as outlined above, and may also affect the risk of breast cancer in females. Human exposure to PCBs and to PAHs is widespread. There is also the possibility of polymorphisms in genes such as the oestrogen sulphotransferases, which may produce changes in enzyme activity that might indicate int…

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Research on environment effects on fertility .. 10
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Past exposure to persistent environmental chemicals (for example, DDT and polychlorinated biphenyls (PCBs)) may have induced effects in humans, as it undoubtedly did in some wildlife species. However, it is less clear that modern (non-persistent) pesticides pose a serious risk to the general public. There are instances in which exposure of men involved in the production or application of particular pesticides has been shown to cause infertility, or where an association between pesticide usage and cryptorchidismor male infertility in farmers has been suggested. However, other detailed studies have failed to find a significant association between pesticide exposure and male or female infertility. Similarly, there are isolated examples in which occupational exposure to non-pesticide chemical…

Research on environment effects on fertility ..9






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Research on environment effects on fertility ..9
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Past exposure to persistent environmental chemicals (for example, DDT and polychlorinated biphenyls (PCBs)) may have induced effects in humans, as it undoubtedly did in some wildlife species. However, it is less clear that modern (non-persistent) pesticides pose a serious risk to the general public. There are instances in which exposure of men involved in the production or application of particular pesticides has been shown to cause infertility, or where an association between pesticide usage and cryptorchidism or male infertility in farmers has been suggested. However, other detailed studies have failed to find a significant association between pesticide exposure and male or female infertility. Similarly, there are isolated examples in which occupational exposure to non-pesticide chemicals (…

Research on environment effects on fertility ..8


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Research on environment effects on fertility ..8
Posted 2017


Maternal smoking can also cause foetal IUGR, which, in turn, has numerous health consequences (see above). Smoking also has adverse effects on development of the reproductive system of foetuses of both sexes, independent of IUGR. Its main consequence in the male is to reduce future sperm counts. redReduced Sertoli cell number is the primary mechanism by which a permanent decrease in sperm count (and testis size) can be induced , and this is the probable explanation for the effect of maternal smoking. As the Sertoli cells orchestrate testicular development, effects on these cells may result in changes in other testicular cells, such as the Leydig cells and foetal germ cells. Leydig cells make the testosterone responsible for masculinization, and abnormal development of the foetal germ cells proba…

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Research on environment effects on fertility ..7
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Effects on future fertility that are induced in foetal/early life
As the reproductive system and its hormonal control systems are established in foetal life, maternal factors that affect the 'foetal environment' may also influence the foetal reproductive system. Because of its own physiological processes, the foetus adapts to its 'environment' and it may be these adaptations that result in adverse effects. For example, girls who were born to mothers in developing countries and then adopted to a Western country as babies have a ~15% risk of precocious puberty at the age of 7–10 years. This may result from a 'conflict' between an adaptation of the foetus to the low nutritional plane of its mother and its childhood development, when food intake is not limiting, although t…

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Research on environment effects on fertility ..6
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A normal calorie intake is necessary for normal pubertal development, the onset of menstruation and for ovulation. During adolescence, there is a change in the accumulation and distribution of fat, including an increase in abdominal adiposity that is closely associated with a reduction in sensitivity of muscle and fat to insulin (insulin resistance), and a compensatory increase in insulin secretion. This physiological elevation in circulating insulin levels results in a reduction of circulating sex hormone binding globulin (SHBG), with consequent release of 'free' (biologically active) oestrogens and androgens, thereby amplifying the effects of these hormones and facilitating sexual maturationFat cells themselves produce metabolic signals — particularly leptin— that can influence the …

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Research on environment effects on fertility ..5
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Effects of lifestyle and diet Increased rates of smoking and consumption of alcohol have been identified in infertile couples. In men, smoking can be associated with minor reductions in sperm count/morphology, but this is inconsistent and not usually associated with altered fertility; however, effects on IVF outcome have been reported. There are also concerns that smoking induces DNA damage in sperm. There is no consistent relationship between moderate alcohol intake and sperm count in men or fertility in women. However, in women, there is unequivocal evidence that smoking negatively impacts on virtually all aspects of fertility. This includes effects on follicle development/ovulation, oocyte pick-up from the ovary and its transport down the fallopian tubes, fertilization and early embryo dev…

Research on environment effects on fertility ..4





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Research on environment effects on fertility ..4
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Environmental and lifestyle effects on fertility in adulthood The effects of photoperiod on humans are demonstrable, as testified by 'seasonal affective disorder'. This also extends to effects on fertility. The incidence of twins and the frequency of births both show seasonal trends (especially in Northern Europe, where photoperiodic changes are most extreme and result in a peak in spring births). This is not caused by a seasonal variation in sexual activity, as differences also occur in fertilization rates and embryo quality in women undergoing in vitro fertilization (IVF). Furthermore, sperm counts in men are consistently ~30% lower during the summer than in the winter. The latter effects could be caused by the higher summer temperature, which can impair sperm production and concept…

Research on environment effects on fertility ..3





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Research on environment effects on Iertility ..3
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Development of the follicle to the point of ovulation takes several month. Early follicular development is not dependent on LH/FSH (the 'gonadotrophins'), but the local and/or endocrine factors responsible for initiation of growth of these follicles are unclear. Later stages of follicle maturation are gonadotrophin-dependent, and in the two weeks preceding ovulation, they are precisely regulated by the cyclical changes in LH and FSH secretion. During these stages, the oocyte undergoes cytoplasmic and nuclear maturation, which enables it to resume meiosis and to prepare for fertilization. During this critical phase, the endocrine environment of the follicle, which is susceptible to the external environment, can profoundly influence oocyte maturation. Unlike the foetal testis, the foeta…

Research on environment effects on fertility ..2





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Research on environment effects on fertility ..2
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In men, the key to fertility is the ejaculation of astronomical numbers of motile sperm (40–250 million per ml). This requires the production of 100–200 million sperm every day, and each sperm takes 10weeks to be produced. Once sperm counts fall below 14–40 million per ml, significant impairment of fertility may occur . This includes an increased time to conceive or, at very low sperm counts (less than 5 million per ml), by more intractable infertility; in these men, sperm are often abnormal in shape and function


The number of sperm produced per day is in turn determined by the numbers of Sertoli cells within the testes. Variation in Sertoli cell number is the main factor that accounts for the wide variation in sperm counts between men . Numbers of Sertoli cells are determined largely by their…