Are sperm counts really falling? What the evidence says

The study behind the headlines

In November 2022 the journal Human Reproduction Update published a systematic review and meta-regression by Hagai Levine and colleagues: "Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries" (doi:10.1093/humupd/dmac035). Pooling studies of men from around the world, the authors estimated that average sperm concentration fell by about 51.6% between 1973 and 2018, from roughly 101 million to 49 million per millilitre, and that total sperm count fell by about 62%.

They also reported that the decline appeared to be faster after 2000 than over the whole period.

What the study does and does not show

• It is a meta-analysis. It combines many earlier studies, which used different populations and methods. The authors adjusted for several factors, but some differences between studies cannot be fully removed.
• It measured count and concentration, not motility (movement) or morphology (shape), which also matter for fertility.
• It does not identify a cause. Lifestyle, environmental exposures and changes in measurement have all been discussed; the paper itself does not settle the question.
• The average remained above common thresholds. The lead author noted that the average stayed above 40 million per millilitre, a level often discussed as a threshold, but that the share of men below it has likely grown.

Independent experts quoted at publication, for example through the UK Science Media Centre, welcomed the size of the analysis but cautioned that measuring a long-term trend in sperm counts is methodologically difficult.

What counts as a "normal" result?

Semen analysis in clinics follows the World Health Organization's laboratory manual. The sixth edition, published in 2021, gives reference values based on more than 3,500 men whose partners conceived within a year. The lower reference limit for sperm concentration is 16 million per millilitre: 95% of these fertile men had a concentration at or above this level.

That definition is important. A result below 16 million does not mean a man is infertile, and a result above it does not guarantee fertility. The sixth edition also moved away from a single "normal" cut-off towards reference distributions, partly for this reason. Because sperm counts vary from one sample to the next, clinics usually repeat an abnormal test before drawing conclusions.

Male factors in infertility

The WHO lists male causes of infertility as problems with semen ejection caused by blocked reproductive tracts, hormonal disorders, testicular failure to produce sperm (for example after varicoceles or chemotherapy), and abnormal sperm shape or movement; anabolic steroid use can also contribute (WHO fact sheet, November 2025). The NHS counts poor-quality semen among the most common identifiable causes of infertility in couples (see how common is infertility?).

Age matters for men too

Men can father children much later in life than women can conceive, but age is not irrelevant. A widely cited study of Icelandic families published in Nature in 2012 by Kong and colleagues found that each additional year of a father's age adds about two new mutations to a child's genome, on average (doi:10.1038/nature11396). Most such mutations are harmless; the authors discussed their possible relevance to the risk of some conditions.

From the archive

Male reproductive function has been a long-standing subject of the research referenced on this site. Three examples from Reproduction, each with a reference page that links to the publisher's version:

• "The effects of radiofrequency electromagnetic radiation on sperm function" (Houston, Nixon, King and colleagues, 2016), a review of the evidence on mobile phone and similar exposures;
• "Vitamin D metabolism, sex hormones, and male reproductive function" (Blomberg Jensen, 2012);
• "The effects of three different exercise modalities on markers of male reproduction in healthy subjects", a randomised trial published in 2017.

How much weight to give each type of study, from laboratory work to randomised trials and meta-analyses, is the subject of how to read a fertility study.

This article explains published research and reference values. It is not medical advice: a GP or fertility clinic can arrange and interpret a semen analysis.

What a semen analysis involves

A semen analysis is a laboratory test of a fresh sample, usually produced at the clinic or delivered quickly. The WHO manual recommends a period of sexual abstinence of a few days before the test, typically between two and seven days, because a very short or very long interval can affect the results. The laboratory measures the volume of the sample, the concentration and total number of sperm, the proportion that move well, and the proportion with a normal shape.

Because results vary naturally from one sample to the next, one abnormal result is usually followed by a second test some weeks later. A specialist can then decide whether further tests, such as hormone measurements, are needed.

Lifestyle and sperm

The factors that the NHS lists as affecting fertility apply to men too: smoking, alcohol, being significantly overweight and some environmental exposures. Sperm take around two to three months to develop, so changes in lifestyle take time to show in a semen analysis. The general guidance for couples planning a pregnancy is summarised in before trying for a baby.

Men, women and age

Men do not have an equivalent of menopause: sperm production continues throughout life, although quality declines gradually. Women's fertility, by contrast, ends with menopause and declines well before it, as explained in when does menopause happen? That asymmetry is one reason fertility discussions often focus on women, even though male factors are involved in a large share of couples having difficulty conceiving.