What Time is It?

A man’s chronological age is actually a poor indicator of the status of his biological clock. Some (admittedly rather rare) 80-year-old men have sexual and reproductive parameters similar to men fifty years their junior. By the same token, some 30 year-olds, though they appear fit and healthy, have biological clocks that have been ticking along furiously and have reached a stage more typically seen in men in their 70s. How can a man tell where his biological clock stands? Fortunately, it’s relatively simple.

When I say “male biological clock” what I’m talking about is the health status of four key physical factors:

  • Semen
  • Sperm
  • Testosterone
  • Erections

The “time” shown on a man’s particular biological clock is a function of how much semen he ejaculates, how many and how healthy his sperm is, his level of testosterone, and the quality and reliability of his erections. Men scoring high on these measures are biologically young regardless of their age, though, as we’ll see, some degradation in the genetic quality of sperm is unavoidable. Many ways exist to improve the four key parameters of sexual health and, thus, rewind (to a certain extent anyway) the male biological clock in men who score low in any of these areas.

Now let’s look at these key factors more closely.


Semen is the milky-colored, somewhat gel-like liquid that spurts out of the penis during orgasm. It is produced not in the testicles, as many men think, but by the walnut-sized prostate gland that sits just below the bladder, and by the seminal vesicles, two pinky-sized glands that feed into the prostate.

Semen is actually a very sophisticated substance. Whole books have been written about it, in fact. Here it’s enough to say that it contains nutrients to keep sperm alive after ejaculation, substances to protect sperm from the chemical environment of the vagina, and special enzymes to make it thin out (liquefy) about 15 minutes after ejaculation. The average amount (volume) of semen expelled by a healthy man in one ejaculation is about a teaspoon (3-5 cubic centimeters). And the semen should spurt or shoot out of the penis, not dribble. Many things, in addition to simple aging, can reduce volume or impair the way the semen is expelled.


A teaspoon of ejaculated semen may not sound like much, but swimming in that teaspoon are usually roughly 250 million sperm, the tadpole-like cells that contain a man’s genetic heritage. Healthy men produce sperm at the prodigious rate of about 60,000 every minute. But each individual sperm cell takes about three months to grow.

Immature sperm are made in the testicles and then move slowly through a long, tightly coiled tube at the back of each testicle called the epididymis. When they leave the epididymis, sperm migrate up two thin pipes called the vas deferens. The vas deferens pass through the prostate gland and join the urethra, which is the tube that passes urine from the bladder.

Healthy sperm swim vigorously in a relatively straight line, their tails are long and whip-like, the heads are well-shaped, and the genetic information they carry is intact. Their swimming ability is key. Although it is only a matter of inches from the back of the vagina, where semen is normally deposited during unprotected sex, to an egg in a fallopian tube, sperm are so tiny that the journey is roughly equivalent to a man running three miles. To reach their target, in other words, sperm have to swim like crazy. Technically, a sperm’s swimming ability is called “motility” and this is a key factor to examine in a good semen analysis.

A sperm’s shape is called its “morphology” and it, too, is measured. Abnormally-shaped sperm often contain genetic errors of one kind or another, which reduce the chances the sperm will fertilize an egg. The more normally-shaped sperm in his semen, the more likely a man will conceive a healthy child from unprotected sex with a woman.

The number, motility, and shape of sperm all generally decline with age, though many other factors can speed up the biological clock governing this particular facet of a man’s overall sexual health. Heat, for example, is bad for sperm. Sperm production plummets in the days following a high fever. Anything that unnaturally warms the testicles, such as taking frequent soaks in a hot tub, will similarly hurt sperm.

The shape of sperm is an indirect measure of the quality of the genetic information they contain, but in recent years it’s become possible to probe the integrity of the genetic information in individual sperm cells. This is a fairly new field of scientific exploration because it’s only recently that the entire human genome has been mapped and rapid techniques for sampling genetic information have been invented. Research to date clearly shows that a range of genetic problems in sperm get worse with age including Autism, hemophilia A, neurofibromatosis, Marfan Syndrome, and polycystic kidney disease. The following graph shows how the risk of having children with some of the most severe birth defects of all types (so-called sentinel birth defects) rises with the age of the father, particularly when the father is older than 35, which is precisely when more and more couples are having children.

A specific example of this phenomenon is illustrated in a study I worked on that showed that older men are much more likely than younger men to father a child with Down syndrome when their female partner is older than 35. Down syndrome is a pattern of mental retardation and altered physical features caused by an extra chromosome 21. We now know that men contribute to the rising incidence of Down syndrome with age, most likely because the overall incidence of genetic problems in their sperm increases with age. In fact the study found that half the cases of Down syndrome in women older than 35 are likely to be sperm-related.

The reason the male influence on Down Syndrome (as well as other genetic defects) has not been recognized before is that the effect is complicated by the age of the female partner. When a woman is younger than 35, the age of the male does not seem to affect the overall risk of having a child with Down Syndrome, whereas when the woman is older than 35, the age of the man has a pronounced effect. What’s going on here? The answer is still being explored, but it seems likely that younger women’s bodies are more efficient at detecting and eliminating embryos with genetic problems. In other words, older men are probably conceiving more genetically-flawed embryos than younger men, but this effect is masked when the woman is young because the flawed embryos either never implant or are spontaneously aborted.

The age of both partners matters when it comes to the risk of having children born with birth defects. The hopeful aspect of this situation is that the various techniques for improving the morphology and overall health of sperm that I will discuss later in the book might actually reduce the potential for birth defects by raising the genetic integrity of the chromosomes contained in those sperm.


A man’s biological clock status is also determined by his levels of testosterone, which drives the development of characteristics such as facial hair, muscle development, and interest in sex. Many other hormones play a role in male sexuality, but testosterone is by far the most prominent and the one most often adjusted with supplements of one type or another. (Note that testosterone isn’t just a “male” hormone—women have it too. Their average levels are much lower than men, but testosterone is as central to the female sex drive as it is for male sex drive. Testosterone also plays a key role in maintaining healthy bones and the cardiovascular system in women. Women with abnormally low testosterone can suffer a variety of ailments such as lack of energy, depression, in addition to losing their sexual desire .)

The normal range of testosterone in men is between 300 and 1100 nanograms (ng) per deciliter (dl) of blood, which is a fairly wide range of “normal” for a bodily component! Levels anywhere in this range confer a normal degree of sexual desire and support normal masculine physical and personality traits. Only when men have either very low or very high testosterone levels are physical or mental changes noticeable.

Men with levels below 300 (a condition called hypogonadism) tend to have little interest in sex, and are usually non-confrontational, socially inhibited, and physically weak. They are also often very intellectual, creative, expressive, and likeable. Men with higher-than normal testosterone tend to be just the reverse: obsessed with sex, competitive, aggressive, extroverted, physical, and tending toward more action-oriented activities or careers. But within the normal range, testosterone levels play only a background role and other aspects of personality dominate. For example, one study of testosterone levels among actors, ministers, football players, physicians, firefighters, professors, and salesmen found only one statistically significant difference in average testosterone levels—that between ministers (whose average testosterone levels were on the low end) and both actors and football players (whose averages were on the high end). But every group displayed wide individual variations—some football players had lower testosterone levels than some ministers, and some professors had higher testosterone levels than many firefighters.

Whatever a man’s basic level, his testosterone fluctuates widely over the course of a day, with peak levels occurring in early morning, dropping by 30 to 40 percent by mid-afternoon.

Testosterone levels usually begin a slow downhill slide of about 1% a year starting around age 30. That loss adds up over the years. Since the average man in the United States can expect to live to age 74, an annual drop of 1% means a 44% drop in testosterone. More importantly, men with low-normal testosterone levels (for instance 400 ng/dl) might hit the threshold of clinically significant testosterone loss by age 55. The signs of below-normal testosterone levels include: fatigue, depressed mood, low or absent sex drive, muscle weakness, and a general feeling of malaise.

Aging, however, isn’t the only reason testosterone levels can fall below normal. Here are just a few factors known to reduce testosterone levels at a much faster rate than simple aging:

  • Diabetes
  • Alcoholism
  • Varicoeles
  • Use of unprescribed testosterone or other supplements, such as anabolic steroids, that boost testosterone
  • Obesity
  • Medications such as glucocorticoids or drugs to treat prostate cancer, such as Proscar.
  • Tumors on the pituitary gland or hypothalamus
  • Adult mumps infection

This all translates into a serious health problem only now beginning to gain widespread recognition. A 2004 article in the New England Journal of Medicine estimated that between two and four million men in the U.S. alone have hypogonadism (defined as testosterone levels below 325 ng/dl).

The prevalence of hypogonadism clearly increases with age, as this chart shows.

NEJM 2004;350:482-92

The following chapter explores ways to restore normal levels of testosterone in hypogonadal men. For now, understand that this is another aspect of the male biological clock that can be safely and effectively “rewound” to restore sex drive, help improve muscle strength, reduce fat, and boost overall energy.


The last measure of male sexual health is the quality and reliability of his erections. Erectile dysfunction (formerly called impotence) is the persistent inability to achieve or maintain an erection adequate for intercourse. It’s an enormous problem that has really only gotten the attention it deserves since the introduction in 1998 of the erection-enhancing drug Viagra. The largest study done to date estimates that between 20 and 30 million men in the US experience some degree of erectile dysfunction, with the incidence increasing steadily with age.

Multinational Assessment of Treatment-Seeking Behavior in Men With Erectile Dysfunction, Ridwan Shabsigh, MD

As with all the other aspects of the male biological clock reviewed above, erectile dysfunction is caused by an interplay of normal aging and a host of other factors that speed up the biological clock including the following:

  • Smoking
  • Diabetes
  • Alcohol
  • Many prescription medications
  • Obesity
  • High cholesterol
  • Injury

Fortunately, erectile dysfunction can almost always been successfully treated these days with either medications or a range of other techniques and technologies detailed in Chapter 3.

Getting Tested

Now we’ve seen the four basic parameters of male sexual health: semen, sperm, testosterone, and erections. Getting a fix on where a man stands—his sexual biological age as opposed to his chronological age—is relatively easy.

Testosterone levels are checked by drawing a blood sample, usually from the arm. Blood samples should be taken in the morning, since that’s when levels are highest. If the levels are below or near 300 ng/dl, another one or two samples may be taken on other days to confirm the first result, since as noted previously, testosterone levels fluctuate daily and seasonally as well.

Whether or not a man has erectile dysfunction is something he and his partner judge for themselves based on their personal experience. All men occasionally can’t get it up, the question is how often that happens and to what degree the man and his partner are bothered by it. These days a man complaining of erectile dysfunction is usually given a trial prescription for an erection-enhancing pill. Only if he can’t take the pill because of other risk factors such as being on a nitrate-containing medication, or if the pill fails to work are more elaborate tests done to try and pinpoint the problem. Such tests can include injection of erection-producing drugs to check the health of the man’s penile arteries and veins, and the use of devices that detect the presence and quality of night-time erections.

The quality of a man’s semen and sperm are assessed on a sample of ejaculate produced by masturbating into a small, sterile plastic container. For some men, this isn’t a big deal. They just go to a bathroom in a clinic or doctor’s office, do their job, and…presto!…a nice, fresh sample which is immediately analyzed. (Some facilities have private rooms for semen collection that often include erotic magazines or videos to help overcome the unnaturalness of the process.) Other men prefer to masturbate at home and bring their sample to the lab. And some men, for religious reasons, need to collect their semen by having intercourse using a special sterile condom (not standard latex or lambskin condoms).

Regardless of how semen is obtained, the sooner it is analyzed, the better. Sperm swim less and less vigorously as the minutes pass after ejaculation. To gauge the vigor of a man’s sperm, his semen should not be more than an hour old. In addition, the sample must not be contaminated by other substances or bacteria, which means men should not have unprotected intercourse to bring themselves to the point of orgasm, and they should not use artificial lubricants during masturbation.

It’s good to plan a semen collection in advance since timing is everything. A man should not “store up” his semen for a long time because sperm in the vas deferens slowly die. If a man doesn’t ejaculate for 4-5 days, his semen will contain more dead sperm than normal. On the other hand if he has ejaculated one or more times in the past two days, his semen volume will be lower than normal. It’s a good idea, therefore, for a man to make sure his last ejaculation was two or three days before the day he collects his semen. (Note: if a man has had a recent high fever or a serious illness or injury, he should talk to his doctor about delaying a semen analysis for about three months to allow his sperm production to recover.)

Sperm counts are given as the number of sperm in each milliliter of semen. Healthy men have between 40 million and 300 million sperm per milliliter, average sperm count is between 60-80 million. Counts below 20 million per milliliter are considered poor, with counts between 20 million and 40 million considered marginal, though possibly fine if other aspects of the sperm, such as their morphology and motility, are good. Men with counts below 20 million may still be fertile, but it may take longer to initiate a pregnancy and the chances are greater than a pregnancy will not occur. Men with high counts are not guaranteed fertile, particularly if an infection or other abnormalities that affect morphology and motility are present.

Interpreting a sperm count correctly requires knowing the total volume of semen in a sample. For example, if a man has 20 million sperm per milliliter of semen, it might be considered low. But if he ejaculates 5 milliliters of semen, his total number of sperm is 100 million—which would be considered perfectly adequate.

Sperm shape is determined by examining semen under a microscope and counting how many appear normal in the small area in view. Sperm are made in such vast quantities that semen from even the healthiest man contains many dead or misshapen sperm. It’s considered normal to have as high as 70% of the sperm in a sample be abnormal or dead, though obviously the fewer such sperm the better for fertility.

I want to emphasize that a low sperm count is almost always the result of some underlying health problem, which can be serious. In other words a low sperm count is a symptom, or clue, that something is wrong, not a disease state in and of itself. A low sperm count is like high fever—the best approach to a fever is not to just throw aspirin at it but to find the underlying problem that is causing the fever and treat that. Not all doctors will tell you that. And many won’t pursue the reason for your low sperm count. But you should. Some of the most common underlying problems are hormonal irregularities, use of over-the-counter steroids, distended veins in the testicles, diabetes, pituitary tumors and even testicular cancer.

Wrapping Up

The male biological clock starts ticking the moment a sperm containing a male “Y” chromosome successfully fertilizes an egg. If all goes well, roughly nine months later a new baby boy enters the world and begins his journey through life. If he is fortunate, he will live long enough to pass through all the important phases of his biological clock, with all of the pleasures and pains that trip entails.

As we’ve seen, however, nature doesn’t hand out the same clock to everyone. Aside from identical twins, every man is biologically unique. Men (and women) age at different rates due to differences in the details of their biological clocks combined with influences such as diet, stress, exercise, injury, disease, and use of substances (such as cigarettes) which speed aging. Now we’ve seen how to tell what “time” a man’s biological clock is tolling: a blood test for testosterone, a semen analysis, and a determination by a man and his partner of the quality of his erections.

But even though a man’s own particular biological clock sets broad limits on his sexuality and fertility, we now know how to offset, reverse, or overcome almost all problems in those two areas. Understanding the ways that genes, aging, and lifestyle factors can erode sexual health is the first step to doing something about it. We’ll now start to take a closer look at specific ways to rewind the clock, starting with the issue of erectile function.


  1. Eskenazi B, Wyrobek AJ, Sloter E. et al. The association of age and semen quality in healthy men. Human Reproduction. 2003 Feb;18(2):447-54.
  2. Dabbs JM, LaRue D, Williams PM. Testosterone and Occupational Choice: Actors, Ministers, and Other Men. Journal of Personality and Social Psychology. 1990;59:1261-1265.
  3. Feldman HA, Goldstein I, Hatzichristou DG, Krane RJ, McKinlay JB. Impotence and its medical and psychosocial correlates: results of the Massachusetts Male Aging Study. Journal of Urology. 1994;151:54-61.
The Male Biological Clock Men's Health Publications Publications

Contact Dr. Fisch