Marine life poisoned with PCBs and other chemicals aren’t the only species on the planet right now with reproductive problems. Men worldwide are experiencing declines in sperm counts, as a recent meta-analysis has uncovered. The article, titled “Temporal trends in sperm count: a systematic review and meta-regression analysis,” analyzed data from 185 studies including a total of 42,935 men over six continents and fifty countries, published between 1973 and 2011. They concluded that both sperm concentration (SC) and total sperm count (TSC) have decreased considerably since 1973. Let’s start with some background then delve into the study’s findings.
How much sperm is normal?
If a man’s sperm concentration falls below 15 million sperm per milliliter of semen, he meets the criteria for infertility according to the World Health Organization. Before 2010, this cutoff value was 20 million/ml. Some argue that this value is too low, and fertility issues can arise with values less than 40 million/ml. A study in 1945 measured sperm concentrations of 100 medical students, and found that the majority had a sperm concentration greater than 60 million/ml, and 65% had a concentration greater than 100 million/ml. There isn’t really a normal value, but it seems certainly that 15 million/ml is far too low.
Sperm concentration is a more reliable marker for fertility status than total sperm number, as that would be determined by semen volume. However, it doesn’t seem clear to me whether or not it’s possible to have a low sperm concentration, but high semen volume, and improve fertility overall (that’s a different question suited for a different post). With age, sperm count, semen volume, and other parameters of semen quality tend to decline (for a more comprehensive review see this article), so using just sperm concentration as a marker of fertility seems okay for now. Recap: it’s not sperm count really it’s sperm concentration that matters. To understand the other parameters of semen analysis see this related post.
Health implications of low sperm count
The reason why this study is important is because there are health consequences to having a low sperm count. Below 40 million/ml, mortality from all causes increases in a dose-dependent manner. That means the lower the concentration, the lower the lifespan. Being obese is associated with lower sperm concentrations as well, suggesting that metabolic abnormalities could be impairing fertility and hormones. This will have to be discussed further in a separate post.
What the researchers did
The researchers analyzed data from eligible studies that measured sperm concentration and total sperm count and analyzed the data based on the year the samples were taken. Then, they took the averages and ran a regression analysis to find a trend. Are sperm counts going up? Down? No pattern?
They grouped people into Western countries (North America, Europe, Australia, and New Zealand) and non-Western countries (South America, Asia, and Africa). Among these groups they further divided men into fertile groups (men who have conceived, termed “fertile” in the paper) and those with unknown fertility status (men who do not have children, termed “unselected” in the paper).
What the researchers found, basically
What this meta-regression analysis found was that there was an overall decline in sperm concentration of between 50-60% everywhere. The decline was by far the greatest among unselected Western men. It was next greatest for fertile Western men. There was a non-significant trend in the opposite direction for fertile men from non-Western nations. Perhaps that could be explained by improved economic wealth or sanitation if the data was from poor countries (the paper doesn’t list all these countries, as there is an enormous amount of data).
Sperm concentration has declined in Western nations by a lot. I’ve been aware of this issue for a while, but it was a nice wake-up call. It is further evidence, to me at least, that despite data showing that our lifespans seem to have increased, our health may be declining. Xenoestrogens, pesticides, stress, and a poor diet may be contributing towards this trend. I mentioned marine wildlife at the beginning of this post. Endocrine disrupting chemicals have disturbed the fertility of marine animals such as orcas. They are hurting us too.
I believe that everything is interconnected. Just like the strength lying in the healthy human physical form, there is health in a normally-shaped spermatozoa. This sperm cell must have the strength to move from the propulsion of its tail. Less fertile men have less motile sperm compared to fertile men.
Tomorrow I’ll discuss some ways to potentially improve sperm health. Stay tuned!