When we hear the term "biological clock," most of us tend to connect that term to women. After all, if the world's oldest dad was able to father a baby at 96 years old, there surely shouldn't be an age limit on male fertility, right?
Not exactly. Stories of men in their 60s or older fathering children tend to fuel the idea that male fertility is eternal, but that’s a misconception. Men also experience the effects of aging with a decrease in fertility over time. To some extent, men—just like women—face a biological clock.
Table of contents:
- At what age are men most fertile?
- When do men stop producing sperm?
- How does age affect male fertility?
- Sperm count decline with age
- Sperm motility decline with age
- Sperm morphology decline with age
- Sperm DNA fragmentation increase with age
- How to improve your fertility as you get older
- How to preserve your fertility
At what age are men most fertile?
Although we haven’t yet pinpointed exactly what age men are most fertile, we know that male fertility decline typically begins at the age of 35 and gets steeper at 40.
The Centers for Disease Control and Prevention (CDC) reports that most men experience significant age-related fertility decline after they reach the age of 40. Other studies show that the decline begins around age 35—in one study, men over the age of 35 had fertility rates of 25%, compared to men under 35 who had fertility rates of 52%. Another study that evaluated the relationship between age and semen parameters also concluded that male fertility decline begins at 35, and suggested that male fertility peaks between 30 and 35.
Bottom line: Men generally see a decrease in fertility beginning at 35, and the decline progresses from there. The age men are most fertile may be between 30 and 35, but we haven’t yet determined a specific window of peak fertility.
At what age do men stop producing sperm?
Men typically never stop producing sperm, but there is a measurable decline in sperm quality as a man ages. The World Health Organization (WHO) has a set of benchmarks, known as semen parameters, for healthy sperm, including count, morphology (shape), and motility (movement). Starting around the age of 35, men may see their semen parameters worsen.
Learn more about how sperm is produced.
How age affects male fertility
Paternal age is among the most significant factors affecting a couple’s chance of conceiving and their pregnancy outcomes. Men over the age of 35–40 typically experience a decrease in sperm health, which affects:
- Pregnancy rates. Pregnancy rates decrease with paternal age. Men will generally see a 52% decrease in fertility rate between their early 30s and their mid-to-late 30s.
- Time to conception. Compared to men 25 years or younger, men 45 years or older are 12.5 times more likely to take over two years to conceive.
- Miscarriage risk. Pregnancy loss between the 6- and 20-week gestation period increases by 27% in fathers 35 years or older. That risk doubles when fathers reach 50.
- Adverse pregnancy outcomes. Pregnancies that involve a male over the age of 45 see an increased risk of birthing complications, and their offspring have an increased risk for adverse birth outcomes.
- Offspring health risks. The probability is still generally low, but studies show that older fathers may be more likely to have children with schizophrenia, bipolar disorder, autism, Down syndrome, or childhood leukemia. It is believed that random mutations in a man's sperm pile up over the years, which can pass genetic mutations to a child and increase their chances of developing a psychological or neurocognitive disorder.
So, why does age have an impact on male fertility? There are four sperm quality parameters that naturally change with age: count, motility, morphology, and DNA fragmentation.
Sperm count and concentration
Sperm count is the number of sperm produced per ejaculation. A low sperm count decreases the chances of getting your partner pregnant. Although scientific research has not found a direct decline of sperm count by age, some studies have found correlations. One study reported a decrease in sperm count of up to 2.6% per year of age. Findings are inconclusive of whether age directly impacts sperm count but regardless, sperm count is just one piece of the fertility puzzle.
Sperm motility refers to the movement of sperm, or how well it "swims." Poor swimmers (low motility) have a decreased chance of pregnancy. According to research, sperm motility is expected to decrease by about 0.8% per year of age. When comparing the sperm in men between the ages 30 to 35 with men over 55, sperm motility decreased by 54%.
A morphology measurement will tell you the percentage of sperm with proper shape, size, and structure. This ideally looks like a smooth oval head with a cap, a midpiece, and a long tail. Generally, men produce many abnormal sperm—morphology measurements as low as 4% are still considered within the normal range. Over time, that number tends to fall. Studies show that sperm morphology decreases by about 0.65% per year of age.
Sperm DNA fragmentation
Sperm DNA fragmentation index refers to the amount of abnormal genetic material (damaged DNA) inside a sperm. The better your sperm quality, the lower this number should be. Studies show that sperm DNA fragmentation increases by 0.3% per year of age.
Bottom line: Nearly every measure of semen quality and male fertility will decline as a man ages, contributing to lower pregnancy rates and a higher risk of adverse pregnancy outcomes.
How men can improve their fertility as they age
Aging is a natural process. Although efforts can be made to improve sperm health, there's no way to stop the effects of age on male fertility completely.
The best way to improve your sperm health is by improving your lifestyle. This can look like:
- Eating a healthier, nutrient-rich diet
- Exercising regularly
- Quitting smoking
- Decreasing alcohol consumption
These are the best ways to improve your sperm health and fertility, and your body will see other benefits from these lifestyle changes as well.
How men can protect their fertility as they age
Making healthy lifestyle changes is great for improving your sperm health, among other things, but it's not a surefire way to prevent the effects of age on fertility. If you want to protect your fertility, freezing your sperm now while it's at its youngest and healthiest can provide you with more options when it comes to when and how you want to start a family.
Learn more about sperm freezing.