Are sperm counts really declining, and should you care?

Scroll social media for five minutes and you'll hear that sperm counts are in freefall, that your cell phone is sterilizing you, and that soy is turning men into something less than men. Most of that is wrong. A smaller, more boring piece of it is right.

What sperm counts actually are, and what "declining" means

A healthy pair of testes produces 200 to 300 million sperm a day. Only about half are viable. Count is just one of roughly ten parameters a urologist will look at. Motility matters. Morphology matters. So does whether the sperm actually carries a full nuclear payload of genetic material. A sperm with two heads or three tails is not going anywhere useful.

When researchers talk about counts, they usually mean concentration: sperm per milliliter. Healthy, fertile men tend to run 60 to 120 million per milliliter. The WHO calls anything above 16 million per milliliter normal. Most men are well above that floor.

The data on trends over time is messier than you'd think. We don't have a clean random sample of 18-year-olds producing specimens every year since 1920. We have selected populations, often men already being worked up for infertility, which is a lousy denominator. One widely cited meta-analysis found average concentrations fell from about 100 million to 50 million per milliliter between 1973 and 2018. That sounds dramatic. But when the same analysis restricted to men of known fertility, the drop was 77 million to 72 million. Much less dramatic.

My read, and Emily's: there's probably been a modest real decline over the past 50 years. Not the apocalypse your feed is selling you.

The things that probably aren't the cause

Let's clear out the social media graveyard.

• Cell phones in your pocket. No biologic plausibility, no convincing evidence. The studies that exist are confounded by how much people talk on the phone, which is not the same as radiation cooking your testicles.
• Soy. Yes, soy contains phytoestrogens, molecules that, if you squint, look a bit like human estrogen. Randomized trial data comparing high-soy diets to low-soy diets shows no effect on sperm count. It's not soy.
• Pesticides. Biologically plausible. Some pesticides have hormonal activity in animals. But the human evidence is mostly case-control studies, which are a deeply flawed design for this kind of question. I'm not ready to dismiss pesticides entirely, but the evidence is weak.
• Laptops on laps. Biologically plausible, because heat does impair sperm production. Scrotal temperature goes up about 2.5 to 3 degrees Celsius with a laptop on your lap. If you're trying to conceive, use a table. But this is unlikely to explain a population-wide trend.

Heat does matter at the individual level. Sperm development requires the testes to sit slightly below body temperature. Frequent sauna, hot tub use, or very tight underwear can drop counts meaningfully. There's a study where men wore extremely tight underwear for months and watched their counts crater, then recover when they took the underwear off. Heavy alcohol and cigarette smoking also lower counts. None of these explain the time trend, because saunas and tight underwear are not sweeping the globe, and smoking has gone down, not up.

The boring answer staring us in the face

If you want to explain a trend, you need something that both affects sperm count and has been rising since the 1970s. Obesity fits cleanly.

The literature here is not subtle. Higher BMI is consistently associated with lower sperm counts across a huge number of studies. And because fat is a hormonally active tissue, producing estrogen-like hormones even in men, there's a plausible mechanism.

More importantly, there's causal evidence. Men who lose weight on GLP-1 medications see their sperm counts and motility improve. That's the kind of evidence that matters clinically. If changing X changes Y, then X is doing something to Y. Obesity almost certainly explains most of the modest decline we've seen.

It's not a sexy explanation, which is probably why you don't hear it on TikTok. "Lose weight" doesn't sell supplements.

Should you care about your own sperm count?

If you're not trying to get someone pregnant, no. Sperm count doesn't correlate with testosterone in the normal range. It doesn't correlate with strength, speed, or anything else people want it to correlate with. Outside of the first three months of life, the testosterone-sperm count link people invoke isn't really there.

If you are trying to conceive, a semen analysis is worth doing early. Men's workups often get skipped, and sperm parameters are movable. Cut back on heavy drinking. Quit smoking. Lay off the sauna for a while. If obesity is in the picture, a GLP-1 is worth discussing. And if your count comes back lower than you'd like, get retested. The coefficient of variation on sperm count is about 50%, compared to 4% for a standard blood test. One measurement tells you very little.

Bottom line

Sperm counts have declined modestly over the past 50 years. The decline is real but overhyped, and the usual suspects on social media, cell phones, soy, laptops, are not the drivers. Obesity almost certainly is. For an individual man, sperm count matters when you're trying to conceive and not much otherwise. If you want to improve yours, the interventions are unglamorous: keep your testicles cool, drink less, don't smoke, and address weight if it's an issue.

I covered this in depth on Wellness, Actually — listen below.

Wellness, Actually Podcast

"What's the deal with declining sperm counts?" — Listen to the full episode, including the week's health news and listener Q&A.