A scientific study published in 2017 reported a substantial decline in sperm concentration among African men over five decades, raising concerns about male reproductive health and the possible factors contributing to infertility.

The study, titled Evidence for Decreasing Sperm Count in African Population from 1965 to 2015, was published in the peer-reviewed journal African Health Sciences in June 2017. It was conducted by Pallav Sengupta, Uchenna Nwagha, Sulagna Dutta, Elzbieta Krajewska-Kulak and Emmanuel Izuka.

According to the research, the analysis found an overall 72.6 per cent decrease in mean sperm concentration in the African populations examined between 1965 and 2015.

The findings were published in volume 17, issue 2, pages 418–427 of the journal. The study is also available through the US National Library of Medicine's PubMed database under PMID 29062337. 

The researchers analysed 14 studies conducted over the 50-year period, covering populations in Nigeria, Tunisia, Tanzania, Libya and Egypt.

The studies involved men in different age groups, with some participants aged between 19 and 55. The researchers examined historical data to establish whether sperm concentration had changed over time.

Their statistical analysis identified a significant downward trend, reporting a correlation coefficient of -0.597 and a p-value of 0.02.

The researchers estimated the mean sperm concentration in the African populations examined at 20.38 million sperm cells per millilitre of semen. They noted that this figure was relatively close to the World Health Organization's 2010 reference threshold of 15 million sperm cells per millilitre.

However, the figure should not be interpreted as proof that African men generally have abnormally low sperm counts. The study combined findings from a limited number of historical studies and did not represent every African country or all men across the continent. 

The researchers also discussed several possible factors associated with declining sperm concentration, including genital tract infections, certain infectious diseases, exposure to pesticides and heavy metals, tobacco smoking and alcohol consumption.

The paper noted that environmental and occupational exposure to toxic substances could affect male reproductive health. However, it did not establish that any single factor was responsible for the overall decline.

Among the environmental concerns discussed was exposure to chemicals such as DDT, endosulfan and malathion, which have been associated with adverse reproductive effects in some studies.

The researchers explained that identifying the precise causes of changes in sperm concentration remains difficult because several factors may contribute simultaneously. 

Nigeria featured prominently in the analysis because several of the 14 studies examined Nigerian populations.

The paper also discussed the country's male infertility burden, citing earlier research suggesting that male-related factors accounted for a substantial proportion of infertility cases among couples experiencing difficulties conceiving.

One environmental issue raised in the paper concerned exposure to fumes and other pollutants from generators, which are widely used in places where electricity supply is unreliable.

Uchenna Nwagha, one of the study's co-authors and a researcher affiliated with the University of Nigeria, was cited in discussions about the potential reproductive effects of environmental toxins.

Nevertheless, generator fumes should be treated as a possible environmental concern rather than an established explanation for the reported 72.6 per cent decline. The analysis did not demonstrate that generator emissions caused the trend.

The study also placed its findings within the context of earlier research on sperm concentration worldwide.

Its authors referred to previous research reporting a 57 per cent decline in mean sperm concentration globally over approximately 35 years. They also discussed earlier findings indicating a decline among European men.

These figures came from separate analyses covering different populations and periods. They should therefore not be treated as direct, like-for-like comparisons proving that Africa experienced the steepest decline worldwide. 

The findings are particularly relevant to discussions about male reproductive health, but their age and methodological limitations are important.

The African analysis covered data collected up to 2015 and was published in 2017. It does not, on its own, establish whether the same trend continued across Africa between 2015 and 2026.

Similarly, the study's estimate of a 72.6 per cent decline describes the trend calculated from the studies included in its analysis. It does not mean that every African man experienced a comparable reduction in sperm concentration.

The findings nevertheless highlight the importance of further research into reproductive health, environmental exposures, infections and lifestyle factors.

For men concerned about fertility, sperm concentration is only one component of semen quality. A proper assessment may also consider sperm movement, shape and other clinical factors.

The study ultimately called for continued scientific investigation into the possible causes of declining sperm concentration and the factors affecting male reproductive health across African populations.