Geographical location seems to make a difference, but the lack of studies conducted in low-income countries makes it difficult to establish a full picture. A paper published this year highlights the fact that even studies from middle-income countries have rarely included the poorest people.
So, twenty years on from the BMJ paper we cannot say we have a complete picture about sperm counts globally. We can say that sperm counts are declining in some places, and this needs to taken seriously. But from the best evidence it seems this crisis is not happening everywhere. And without new and carefully controlled studies, we are likely to spend many more years in the dark over this issue. It is only by looking carefully at where counts are and are not falling, using the most accurate methods available, that we might find any clue to the cause.
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