The author previously wrote a blog based on an International conference presentation (2018) which was subsequently published by Prof Levine from Israel showing that there is a global decline in sperm concentration followed by a large press coverage and concern about male fertility decreasing. In November 2022 a second meta-analysis on sperm concentration decline globally appeared and it now incorporated a few countries in Africa and South America among others not previously considered. This again had a huge press coverage that bordered on paranoia and hysteria and warning about infertility on the increase and men’s doomsday. The emphasis in this blog is to warn against a correlation between decreasing sperm concentration and infertility per se. But before I allude to this systematically from many points of view, I want to congratulate the authors of the two Levine papers for a very in depth approach to establish if there is indeed a sperm concentration decline globally? As stated in the first blog I am in total agreement with Lars Björndahl, reputable clinical spermatologists, that we “respect epidemiological studies but we should remember that mathematical correlations don’t prove that there is a causative relation”!
By and large there appears to be a decline in sperm concentration although there are some weaknesses, particularly in selecting the older literature showing that sperm concentration averaged about 100 million sperm per ml in the 1980’s compared to averages between 40 and 50 million sperm/ml currently. It has been shown in the previous blog that the methodology used in the 1950’s/60’s tended to greatly over estimate sperm concentration. Typically, semen was diluted using a white cell pipette and a sub sample was used to determine sperm concentration in a Neubauer haemocytometer. So it is rather the dilution technique than the haemocytometer (gold standard) that may have led to over estimation and possibly less strict rules to follow which sperm can be counted and which should be ignored when using the haemocytometer. Despite these shortcomings studies in Cape Town covering the period 1960 to 2000 showed that sperm concentration was about 49 million/ml in the 1960’s compared to about 47 million/ml in early 2000 which was not significantly different. Currently many investigators use a Makler chamber or even a depth calibrated chamber such as Leja. Not only does there appear to be big differences in sperm concentration measurement using different types of cell counting chambers but the chambered slides such as Leja tend to largely under estimate sperm concentration unless the Segre-Silberberg effect is carefully taken into consideration.
In the WHO manual on semen analysis semen quality can only be judged as normal/abnormal when a whole range of sperm parameters are measured (e.g. Percentage sperm motility, progressive motility, morphology, vitality, fragmentation). Even then a very good sample can only really be equated to good health and not fertility as such. Further, modern trends to evaluate sperm quality and potential fertility involve a whole battery of tests such as hyperactivation, reactive oxygen species, mitochondrial membrane potential and many more. Many of these tests in combination have been shown to relate to the potential to fertilize the oocyte. Furthermore, a large body of information re short abstinence during the last decade casts huge doubts on the value of using a declining/low sperm concentrations per se as leading to a fertility problem. After 2 hours of abstinence compared to three days’ abstinence sperm concentration and sperm volume fall significantly and even below WHO cut-off values based on normal values. But sperm motility, progressive sperm motility increase whereas sperm fragmentation decreases significantly after 2h abstinence compared to three days of abstinence. Accordingly, after a short abstinence period sperm functionality improves despite a huge decrease in sperm concentration. This at least partly shows that even after three days of abstinence sperm show signs of aging/senility.
In the second meta-analysis study some countries in Africa and South America have now been included. But while it may be possible that there is a decline in sperm concentration globally it clearly does not relate to a decrease in fertility over the last 60 years. Possibly the best way to investigate this is by looking at the average birth rate or population growth and establish if the increase in populations have declined over the same period as a sharp decline in sperm concentration was evident according to the meta-analysis. In 2000 the population in Africa was 800 million and barely more than 20 years later it is now 1.4 billion. A 600 million increase in just 22 years! Current figures for Uganda indicate that an average family has 5 children. In Africa growth rate is above 2%. In South America the population will increase from 438 million to nearly 500 million by 2055 and then decline steeply. In China population decline had to do with restrictions to a one child family and by the end of the century Asia will have more than 4 billion people. In India alone the population increased from 450.55 million to 1.41 billion people from 1960 to 2021. This is a growth of 212.4 percent in 61 years. Despite the doomsday prophets re male infertility even in the USA the slow growth rate is 0.5% and will only reach no further growth in 2100 according to UN estimates. In real terms the USA population will increase by 60 million in the period 2023 to 2100 (Fig. 1):
Fig. 1: Source UN. The decline in USA from about 1.5% in 1950 to less than 1% in the 1960’s is largely due to the contraceptive pill and other socio-economic factors. Growth rate declines in USA but overall population will increase in the next about 80 years by more than 60 million.
Does Europe provide a more negative scenario? The population of Europe was estimated to have increased by approximately 0.4 percent in 2020, reaching an overall total of approximately 747 million people. If sperm concentration was related to fertility here it shows an upward trend. Since 1950, Europe’s population growth rate has never exceeded one percent, and from 2000 to 2008 there was an increase in population growth in Europe. The decline in 2021-22 may relate to Covid.
The second meta-analysis furthermore clearly shows that it is only in the USA, Europe and Australia that the decline in sperm concentration was significant. These countries with their lavish lifestyles, high carbohydrate diets, junk food, alcohol consumption, obesity are all factors mitigating less ideal circumstances for good sperm production, leave alone the stress factors associated with declining economies.
I want to include a large section which appeared in the first blog again as it helps to provide a more balanced perspective on the sperm concentration paranoia: “It must be made clear that several countries in central Europe experience more deaths than births and accordingly a decrease in population growth. But to use the Lars Björndahl analogy, it will be wrong to equate this simply to a decline in sperm numbers but even if it represents a decline it potentially relates to many other socio-economic factors. Which factors? There are many. In modern Europe and also in many instances elsewhere, there is an increasing number of females that first select a career and then in the later thirties decide to start a family but then their fertility is compromised because of the poorer quality of the oocytes (late thirties). In a modern Europe with a competitive environment there are many stresses imposed on males and females leave alone life style factors such as obesity, smoking and many other factors (mentioned above) such as older males and younger female partners. The fact is they become part of the sample showing a so called decline in sperm number. Yet it seems to be mainly socio-economic.
Van der Horst and Maree (2014) has furthermore shown that there is a natural decline in sperm quality in monogamous species and also largely relates to humans. This is an adaptation to a decrease in sperm competition. Just consider for a moment that in humans and gorilla’s sperm quality is poor when compared to the promiscuous species such as chimpanzees (in chimpanzees and also in monkeys the average sperm concentration may be 5 to 10 fold that of humans and percentage sperm motility considerably higher).
Finally, it is evident that due to chemical pollution (plastics) and environmental estrogens, and life style overall fertility will possibly be severely affected. Of course this needs our serious attention but I beg to relate a decline in sperm numbers for Homo sapiens as dooms day is just not credible. It is surely multi-factorial. Males with declining fertility potential and decline in sperm concentration need to be convinced to first change their lifestyle. (…) But please, the evidence of zero sperm in the next generation and even well beyond is by all good scientific arguments not reasonable”. The international Press must also take more care not to exaggerate studies that report on declining sperm concentration: a BBC report suggested that by 2045 no males will have sperm. This is not only unacceptable and irresponsible reporting, it is paranoia!
Prof Gerhard van der Horst (PhD, PhD)
Senior Consultant
MICROPTIC S.L. (A Hamilton Thorne Company)
References:
https://www.obstetricgynecoljournal.com/articles/cjog-aid1122.pdf
https://academic.oup.com/humupd/advance-article/doi/10.1093/humupd/dmac035/6824414
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