Creatine and Fertility: Impact on Egg, Sperm, and Pregnancy

Creatine is deeply involved in the biology of reproduction, but not in the way most gym-goers or supplement shoppers would expect. Sperm rely on a creatine-powered energy shuttle to keep their tails beating, the uterine lining ramps up creatine production right around the window of fertilization and implantation, and pregnancy itself reshapes how a woman’s body handles creatine. Whether supplementing with creatine actually improves fertility outcomes is a different question, and the honest answer is that the human evidence is still in its early stages.

How Creatine Powers Sperm

A sperm cell faces a unique engineering problem. Its engine (the mitochondria packed into the midpiece, just behind the head) sits in one spot, while the tail that needs that energy extends far away. To bridge the gap, many species use what researchers call a phosphocreatine shuttle: mitochondria generate energy and load it onto creatine, which then ferries it down the tail to where the motor proteins consume it. Work on sea urchin sperm showed that when creatine kinase was specifically inactivated, the tight coupling between energy production and tail movement broke down, confirming that the shuttle is an essential link in those cells.¹

Human sperm also contain creatine kinase and carry total creatine concentrations in the range of 8 to 15 millimolar, with additional creatine present in the surrounding seminal fluid.² That said, humans seem to have a backup plan. When researchers inhibited creatine kinase in human sperm, the percentage of cells that kept beating their tails did not change. Velocities did drop under certain metabolic conditions, and progressive motility suffered, but cells were not immobilized entirely. The conclusion: creatine kinase is not strictly required for human sperm movement, but it supplements energy delivery when other fuel sources are limited.³ In practical terms, this means creatine is part of the energy toolkit human sperm carry, even if they can limp along without it.

Creatine Kinase as a Marker of Sperm Problems

Here is where things get counterintuitive. If creatine kinase helps sperm, you might expect more of it to be better. But in clinical studies, higher creatine kinase activity in sperm is actually associated with worse fertility. The reason has to do with sperm maturation. As sperm develop and shed excess cytoplasm, they normally lose much of their creatine kinase along with it. Sperm that retain too much cytoplasm, a sign of incomplete maturation, end up with abnormally high creatine kinase levels.

A study comparing men with different degrees of low sperm count found that the most severely affected group had creatine kinase levels about 18 times higher per sperm cell than men with moderate or mild low counts, and over 100 times higher than healthy donors.⁴ Another study confirmed that semen creatine kinase was negatively correlated with sperm concentration and progressive motility, meaning that as creatine kinase went up, sperm quality went down.⁵ Older research found significantly different enzyme levels between men with normal sperm and those with poor count and motility, though individual values overlapped too much for the measurement to work as a standalone diagnostic test.⁶

So creatine kinase in semen is more useful as a red flag for immature sperm than as something you would want to boost. This distinction matters because it separates the enzyme’s role as a biomarker from the broader question of whether supplementing creatine could help.

Can Creatine Supplements Improve Male Fertility?

The most direct human evidence comes from a small pilot trial published in 2025. Researchers gave creatine, creatine combined with ubiquinol (a form of CoQ10), or a placebo to men with normal and low sperm counts for eight weeks. The combined creatine-plus-ubiquinol group showed an average rise of about 7 million sperm per milliliter, though this did not reach statistical significance on its own. What was more striking: 60 percent of all men who received creatine (with or without ubiquinol) had higher sperm concentrations at the end of the study, compared to only 20 percent of controls. Among the men who started with low counts, every single one in the creatine groups saw improvement, while those on placebo stayed flat or got worse.⁷

That is an encouraging signal, but it is a single small trial and it combined creatine with another supplement in its best-performing arm. It would be premature to call creatine a proven treatment for male infertility based on this alone.

Animal research adds biological plausibility. Mice genetically unable to produce their own creatine (due to a knocked-out GAMT gene) have significantly reduced sperm counts and lower fertilization rates. When these mice were given creatine supplements, their sperm counts rose significantly, fertilization rates improved, and some of the structural damage in their testes was partially reversed.⁸ Separately, research in fish showed that creatine reduced oxidative stress and DNA fragmentation in sperm, suggesting an antioxidant role beyond simple energy provision.⁹ And in goat sperm preservation studies, adding creatine to the freezing solution significantly improved motility, viability, and membrane integrity after thawing, which has practical implications for animal breeding and potentially for human fertility clinics down the road.¹⁰

Creatine in the Uterus

Creatine’s role in reproduction is not just about sperm. The uterine lining, or endometrium, has its own active creatine metabolism. Researchers have confirmed that human endometrial tissue contains all the enzymes needed to both synthesize creatine locally and import it from the bloodstream.¹¹ This activity is not constant throughout the menstrual cycle. Creatine kinase levels in the endometrium are roughly three and a half times higher during the secretory phase (the post-ovulation window when implantation occurs) compared to the proliferative phase earlier in the cycle.¹² The enzymes responsible for creatine synthesis and transport also peak around the early secretory phase, right when an embryo would be arriving and trying to implant.¹³

One intriguing finding from the same research: the creatine transporter, the protein that pulls creatine into cells, was expressed at higher levels during the proliferative phase in women with primary infertility compared to fertile women. What this means is not yet clear. It could reflect a compensatory response to some underlying energy deficit, or it could be an incidental difference. Researchers have suggested that understanding uterine creatine metabolism more fully could eventually lead to strategies for improving embryo implantation.¹⁴

Dietary Creatine and Women’s Reproductive Health

The largest study looking at creatine intake and women’s reproductive health is not a supplementation trial but an observational analysis of dietary habits. Using data from over 4,500 women in the U.S., researchers estimated how much creatine women consumed through food (primarily from meat and fish) and compared reproductive outcomes between those meeting a recommended threshold and those falling short. Women who consumed at least 13 milligrams of creatine per kilogram of body weight daily had about 25 percent lower odds of irregular menstrual periods compared to those below that level. The low-intake group also showed higher rates of several other reproductive issues, including fetal macrosomia, pelvic infection, hysterectomy, and oophorectomy.¹⁵

There are two important caveats. First, this is observational data, so it cannot prove that creatine itself caused these differences. Women who eat more creatine-rich foods also tend to eat more protein in general, and dietary patterns come bundled with other nutritional and lifestyle factors. Second, the threshold of 13 milligrams per kilogram of body weight per day is not easy for everyone to hit through food alone, particularly for vegetarians and vegans, who get virtually no dietary creatine. For a 65-kilogram woman, the threshold would mean eating roughly 845 milligrams of creatine daily, which translates to about 400 grams of beef or a similar amount of fish. The average intake in the study was about 10.5 milligrams per kilogram, meaning most women in the sample fell below the recommended level.

The Endometriosis Question

Not all of creatine’s connections to female reproductive health point in a positive direction. A 2024 study found that creatine accumulates in the peritoneal fluid and in endometriotic cells of women with endometriosis. In lab experiments, creatine reduced iron-driven cell death (a process called ferroptosis) in these cells, essentially helping them survive conditions that would normally kill them. The researchers identified a specific mechanism: creatine binds to a protein called prion protein (PrP), reduces iron uptake into cells, and thereby protects endometriotic tissue from oxidative damage.¹⁶

This does not mean creatine causes endometriosis. The finding is that endometriotic cells produce more creatine than normal cells and exploit it for survival. Whether supplementing creatine orally would worsen existing endometriosis or increase risk in susceptible women is an open question that no clinical study has addressed. But for women with endometriosis who are considering creatine supplements, it is worth flagging as an area of active investigation.

Oocyte Health and Environmental Stress

A less-discussed angle involves creatine’s role in egg quality. Research on the effects of microplastic exposure on pig oocytes found that these pollutants disrupted creatine metabolism within the eggs, leading to lower creatine levels alongside increased oxidative stress, DNA damage, and impaired maturation.¹⁷ This is an animal model and a specific environmental stressor, so direct conclusions about human egg quality and creatine supplementation would be a stretch. But it underscores that creatine metabolism matters at the level of the individual egg cell, not just the uterus or the whole organism. If creatine is part of the energy and antioxidant system that keeps oocytes healthy, disrupting it may be one pathway through which environmental exposures harm fertility.

Creatine During Pregnancy

Pregnancy changes how the body handles creatine. In animal models, plasma creatine and urinary creatine excretion both drop significantly during gestation, while the kidneys ramp up production of the enzymes needed to make more creatine.¹⁸ In human women, a prospective study tracking creatine markers throughout pregnancy found that plasma creatine stayed stable while urinary creatine fell in late pregnancy, suggesting the body was conserving creatine rather than excreting it.¹⁹ This shift in creatine handling looks like a metabolic adaptation to the growing energy demands of the fetus.

How creatine reaches the fetus is surprisingly complicated. The human placenta contains all the molecular machinery to synthesize creatine and to transport it across.²⁰ But in sheep, even when researchers tripled or quadrupled the mother’s plasma creatine with a 10-day infusion, fetal creatine levels did not budge. Labeled creatine given to the mother did not appear in fetal blood either, suggesting that in sheep at least, creatine does not cross the placenta directly. Instead, the placenta appeared to release a creatine precursor (GAA) back into the maternal circulation.²¹ Whether the human placenta behaves the same way is not settled; the presence of creatine transporters in the human syncytiotrophoblast hints that direct transfer may be possible in humans even if it is not in sheep.

The reason researchers care so much about getting creatine to the fetus is birth asphyxia. When a baby is deprived of oxygen during delivery, the resulting brain injury can be devastating. In fetal sheep studies, creatine supplementation during pregnancy has been shown to reduce the metabolic and oxidative brain damage caused by acute oxygen deprivation.²² Reviewers have argued that because creatine protects mitochondrial function under low-oxygen conditions, it could serve as a prophylactic against brain, heart, kidney, and diaphragm damage in high-risk births, potentially across multiple organs simultaneously.²³ This remains in the preclinical and early clinical testing phase, however.

Safety of Creatine in Pregnancy

Creatine monohydrate has a strong safety record in healthy adults. A 2014 review noted that long-term use appears safe and that creatine’s neuroprotective properties have been documented across various populations, including elderly adults.²⁴ But pregnancy is a different situation, and for many years there were no clinical trials of creatine in pregnant women at all.

That has recently started to change. A 2025 open-label dose-escalation trial tested creatine monohydrate in pregnant women, gradually increasing doses. Participants reported no major adverse events or side effects.²⁵ While this is a preliminary safety study and not designed to test whether creatine improved outcomes, the absence of adverse events is a necessary first step before larger trials can proceed. Larger randomized trials are presumably in the pipeline, given the animal evidence supporting fetal neuroprotection.

For people not currently pregnant, the general safety picture of creatine monohydrate is well established at standard doses (typically 3 to 5 grams per day). The concern for reproductive-age adults is not toxicity but rather the lack of large trials specifically measuring fertility-related endpoints. If you are actively trying to conceive and considering creatine, the biological rationale is there, but the clinical proof that it improves your chances is not yet strong enough for anyone to make a confident recommendation. That goes for both men and women.

What Vegetarians and Vegans Should Know

Because dietary creatine comes almost exclusively from animal products, people who eat little or no meat tend to have lower baseline creatine stores. This is well documented in the sports nutrition literature and is part of why vegetarians often see larger performance gains from creatine supplementation than omnivores. In the context of fertility, the NHANES data showing associations between higher dietary creatine and better reproductive outcomes in women takes on extra relevance for this group.²⁶ The average woman in that study was already below the recommended dietary creatine threshold, and vegetarians and vegans would be expected to fall even further below it.

This does not mean that vegetarians are destined for fertility problems. The body synthesizes creatine from amino acids (glycine, arginine, and methionine), and this internal production covers basal needs in most people. But if creatine availability in the uterus and ovaries does turn out to matter for implantation and egg quality, people who start from lower stores might hypothetically benefit more from supplementation. That remains speculative until direct trials are done, but it is a reasonable question for future research to address, and it is a question that vegetarians and vegans are already asking their doctors about.