Where Have All The Sperm Gone?

29. August 2017
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With regard to men in western countries, sperm concentration has declined by more than 50 percent since the 1970s. Experts do not see any sperm crisis, but they still advise studying the trend. There are currently several explanatory approaches.

The concentration of sperm in men from North America, Europe, Australia and New Zealand decreased by 52.4 per cent between 1973 and 2011. During the same period, the total number of sperm per ejaculation decreased by 59.3 per cent. Hagai Levine,epidemiologist at the Hadassah-Hebrew University in Israel, came to this result. Looking however at men from South America, Asia and Africa he did not find any statistically significant negative trends. Levine was not able to analyse other parameters, such as the mobility of sperm.

Good data, bad data

For his systematic review involving meta-analyses Levine found 185 studies from the period 1973 to 2011 involving a total of 42,935 men. In all cases semen samples existed which were able to be studied. There was good data at hand for men from North America, Europe, Australia and New Zealand. Whether the difference in sperm concentration between men from these lands and men from South America, Asia and Africa is in actuality so great is something that cannot be deduced from the available data; as Levine alludes to, the “poor data” derived from outside Western countries is the reason for this. Even though a comparison may not be possible, it is worth looking more closely at the data from the Western countries and searching for explanations.



Sperm concentration (a) as total (b) for men from western countries and from other regions. In the group labelled “fertile” there was information available on virility – for example, through previous paternity events. Screenshot DocCheck / © Hagai Levine et al., Hum Reprod Update

Looking around for causes

Hagai Levine

Hagai Levine © Hadassah Medical Center

Levine has not investigated possible reasons for his trend. Nevertheless, he reports on hypotheses: “From previous studies, we know that exposure to endocrine disruptors in-utero can disrupt the development of the male reproductive system and fertility potential. Later in life, chemicals such as pesticides or tobacco smoke, as well as excess body weight, then come on top of this. “If regional differences end up being confirmed by better studies, he sees variable exposure to particular substances, especially to pesticides, as an explanation.

At the same time, he advises that the trend be taken seriously: “Our data show that the proportion of men below the threshold of subfertility or infertility is increasing”. Clear consequences with regard to population growth will first be seen when a significant proportion of the population exhibits a very low fertility rate, he says. Among experts, the reactions to this assessment are rather divided.

“No reason to be worried”

Sabine Kliesch

Sabine Kliesch © University Hospital Münster

“There is, in my opinion, no reason to be concerned”, Professor Dr. Sabine Kliesch from the Center for Reproductive Medicine and Andrology, University Hospital Münster (Germany), offers as her comment in response to the study. “All the changes indicated occur within a highly normal range, this means that a limitation of procreative capacity is not something that would be expected based on the statistically observed changes.”

She makes mention of observed variations within the range of normality which occur when looking at the one and very same patient. Somewhat more decisive is the number or concentration of forward-moving sperm cells than the total number of sperm, she says. Only these would ever reach ovum cells at all. “And in this respect this analysis has nothing to say”, Kliesch says, giving food for thought.

What role chemicals are playing here she cannot say: “There may be an association here, but causality needs to be tested”. Its better understood that substances change the functions found in sperm more so than the number of them, she states. “The number of such chemicals is large, ranging from intake of medications, external vices such as smoking, to accompanying diseases, and even altered analytical methods”.

The age of women as a real problem

Stefan Schlatt

Stefan Schlatt © UKM-Fotozentrale

Professor Stefan Schlatt, Director of the Center for Reproductive Medicine in Münster, also gives the all-clear signal. The World Health Organisation (WHO) consider cell counts of 39 million sperm per ejaculate or 15 million sperm per milliliter to be the reference levels for male infertility. “A small group of men will therefore over time fall below this figure, but that is not a problem”, says Schlatt. “The true problem with fertility between partners is age – and not the age of the man, but rather that of the woman”.

Whether or not the often proclaimed sperm crisis exists he cannot say. “This study has the benefit, however, that it clearly shows one thing: at least something does hold true about this theory that the numbers are falling. The extent to which fertility of men is decreasing cannot be provided by this study”.

Schlatt can merely speculate on the possible reasons: “The mobile phone in the trouser pocket, endocrine disruptors in the environment, acetylsalicylic acid in painkillers, some other hormone metabolism due to being overweight, or the abusive use of hormones in body building: all these are suspected of being causes of fewer sperm”.

He considers a combination of several factors likely, except for smoking: “This is definitely bad for the sperm count; This has been scientifically verified“. Levine’s work should therefore act as an incentive to further examine the thesis and then, if necessary, to investigate the causes.

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Image copyright: geralt, flickr / Licence: CC0

Comments are exhausted yet.


Dr Franz Nanni
Dr Franz Nanni

Oestrogens… in beef, chickens… and and and.. ? only a question.. !

#3 |
Angelica Ursula Landau
Angelica Ursula Landau

Very good.
About the Handy in trousers, this is a possibility, why not ?
Everybody carries a Handy in trouserpocket because it’s easy to be reached, at every moment.
The microwave may be another reason. But not so steady.

#2 |
Medical physicist

If the mean hours since previous ejaculation was less in the later studies could this account for the difference? In which case the cause could be about social trends instead of chemical toxicity etc.

#1 |
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