The Trade-Off Between Fertility and Longevity, and Causes of Precocious Puberty

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A century ago, the age of first menstruation averaged as late as nearly 17. Why is sexual maturity coming so much earlier now?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Healthy Seventh-day Adventist vegetarians may be longest living, but might that come at a cost? A semen analysis at a fertility clinic in Loma Linda, CA, home to a large population of Adventists, raised questions about their sperm quality. Though still within the normal range, vegetarians had about a 25 percent lower sperm count. The few vegans tested also had a lower sperm concentration, but they made up for that with their 30 percent greater ejaculate volume. The vegans did have significantly fewer activated sperm, though, which is a sign of decreased fertility. The researchers suggested soy consumption as a possible mechanism, as Adventist vegetarians in California average about a half serving a day of plant-based meats, many of which contain soy. Soy phytoestrogens have been put to the test, though, and months of consuming up to the equivalent of nearly 20 servings of soy a day did not result in any adverse effects on sperm parameters.

There were only five vegans in the study, so the sperm quality findings could just be a fluke, but if verified, this could reflect an evolutionary tradeoff between fertility and lifespan first proposed nearly a century ago. Using a finely tuned laser, it’s possible to selectively destroy individual cells as the tiny roundworm C. elegans develops, and terminating the cells that give rise to sperm and eggs significantly extends lifespan. The same phenomenon can be demonstrated in fruit flies, potentially shifting the body’s priorities from reproduction to survival.

The fertility vs. longevity tradeoff may be one of the reasons why spaying and neutering our pets can extend their lives. Based on a study of millions of dogs and cats, sterilized dogs live about 20 percent longer than “intact” dogs, and spayed cats live about 40 percent longer, and neutered cats a remarkable 60 percent longer.

What about men who have been castrated? Eunuchs seem to live 25 percent longer than non-castrated men. Up until the 1950s in the United States, the so-called “feebleminded” were involuntary sterilized by the state in a eugenics program upheld by none other than Oliver Wendell Holmes, who wrote for the majority on the Supreme Court: “[S]ociety can prevent those who are manifestly unfit from continuing their kind. The principle that sustains compulsory vaccination is broad enough to cover cutting the Fallopian tubes.” The heinous practice of compulsory sterilization did allow for a natural experiment, though, and one mental institution found that castrated men lived about 14 years longer than intact men in the same hospital.

A genealogy database of nearly 200,000 men and women across three centuries in 16 countries found that those who had fewer children seemed to live longer. Centenarians, for example, were found to have fewer children at later ages. This is not to suggest that having fewer children will make you live longer, but rather that constitutional factors that enhance human lifespan may come at the expense of reduced reproductive potential, another example of the antagonistic pleiotropy theory I talked about before. For example, selection for lifespan extension in model organisms can lead to longer-lived animals, but with reduced reproductive capacity. It makes intuitive sense when you consider the context of food scarcity.

In lean times, it makes sense to put off reproduction until the return of more favorable conditions to ensure long-term survival. In the infamous Minnesota Starvation Study that used conscientious objectors as guinea pigs during World War II, the study subjects rapidly lost their libidos after their calorie intake was cut in half. As one of them put it, “I have no more sexual feeling than a sick oyster.” The same calorie restriction that extends the lives of animals can also cause a reduction in the number of progeny. If you read my book How Not to Age, you’ll be familiar with the nutrient-sensing aging pathways—IGF-1, mTOR, and AMPK—that create kind of a seesaw between tissue acceleration and reproduction on one side, and tissue preservation and rejuvenation on the other. Thankfully, we can shift the weight to a more optimal balance with diet.

The later girls start their periods, the longer they tend to live. Each year later is associated with significantly lower risk of dying from heart disease and stroke, plateauing out with the lowest overall mortality among those who don’t start menstruating until age 15. Isn’t 15 a little late? It didn’t used to be. A century ago, the age of first menstruation averaged as late as nearly 17. Similarly, the age of breast development has dropped an average of about three months per decade over the last half century around the world––down to nine or 10 years old in the United States, necessitating a change in textbook definitions of “premature” puberty.

Earlier breast development (before age 10, versus 12 or 13) is associated with as much as 23 percent greater breast cancer risk later in life. And each year later a girl starts to menstruate is linked to significantly lower risk of cancers of the uterus, liver, skin, bladder, colon, lung, and breast. Thankfully, the age of puberty is something over which we have a degree of control.

Higher levels of IGF-1 are associated with earlier sexual maturity, so it’s no surprise that girls eating more animal protein experience puberty significantly earlier––an effect not seen with protein from plants. A meta-analysis of 16 studies on diet and development found that one’s first period appears to start earlier by two months for each additional one gram per day of animal protein intake in childhood. So, for example, at seven years old, girls consuming more than 12 servings of meat a week had 75 percent greater odds of menstruating within the next five years or so compared to girls at that age eating less than four servings a week, and this relationship was seen for both red meat and poultry consumption. IGF-1 and other aging pathways may not fully explain these findings, however, as persistent pollutants that build up in meat, like DDT, have also been linked to precocious puberty.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Healthy Seventh-day Adventist vegetarians may be longest living, but might that come at a cost? A semen analysis at a fertility clinic in Loma Linda, CA, home to a large population of Adventists, raised questions about their sperm quality. Though still within the normal range, vegetarians had about a 25 percent lower sperm count. The few vegans tested also had a lower sperm concentration, but they made up for that with their 30 percent greater ejaculate volume. The vegans did have significantly fewer activated sperm, though, which is a sign of decreased fertility. The researchers suggested soy consumption as a possible mechanism, as Adventist vegetarians in California average about a half serving a day of plant-based meats, many of which contain soy. Soy phytoestrogens have been put to the test, though, and months of consuming up to the equivalent of nearly 20 servings of soy a day did not result in any adverse effects on sperm parameters.

There were only five vegans in the study, so the sperm quality findings could just be a fluke, but if verified, this could reflect an evolutionary tradeoff between fertility and lifespan first proposed nearly a century ago. Using a finely tuned laser, it’s possible to selectively destroy individual cells as the tiny roundworm C. elegans develops, and terminating the cells that give rise to sperm and eggs significantly extends lifespan. The same phenomenon can be demonstrated in fruit flies, potentially shifting the body’s priorities from reproduction to survival.

The fertility vs. longevity tradeoff may be one of the reasons why spaying and neutering our pets can extend their lives. Based on a study of millions of dogs and cats, sterilized dogs live about 20 percent longer than “intact” dogs, and spayed cats live about 40 percent longer, and neutered cats a remarkable 60 percent longer.

What about men who have been castrated? Eunuchs seem to live 25 percent longer than non-castrated men. Up until the 1950s in the United States, the so-called “feebleminded” were involuntary sterilized by the state in a eugenics program upheld by none other than Oliver Wendell Holmes, who wrote for the majority on the Supreme Court: “[S]ociety can prevent those who are manifestly unfit from continuing their kind. The principle that sustains compulsory vaccination is broad enough to cover cutting the Fallopian tubes.” The heinous practice of compulsory sterilization did allow for a natural experiment, though, and one mental institution found that castrated men lived about 14 years longer than intact men in the same hospital.

A genealogy database of nearly 200,000 men and women across three centuries in 16 countries found that those who had fewer children seemed to live longer. Centenarians, for example, were found to have fewer children at later ages. This is not to suggest that having fewer children will make you live longer, but rather that constitutional factors that enhance human lifespan may come at the expense of reduced reproductive potential, another example of the antagonistic pleiotropy theory I talked about before. For example, selection for lifespan extension in model organisms can lead to longer-lived animals, but with reduced reproductive capacity. It makes intuitive sense when you consider the context of food scarcity.

In lean times, it makes sense to put off reproduction until the return of more favorable conditions to ensure long-term survival. In the infamous Minnesota Starvation Study that used conscientious objectors as guinea pigs during World War II, the study subjects rapidly lost their libidos after their calorie intake was cut in half. As one of them put it, “I have no more sexual feeling than a sick oyster.” The same calorie restriction that extends the lives of animals can also cause a reduction in the number of progeny. If you read my book How Not to Age, you’ll be familiar with the nutrient-sensing aging pathways—IGF-1, mTOR, and AMPK—that create kind of a seesaw between tissue acceleration and reproduction on one side, and tissue preservation and rejuvenation on the other. Thankfully, we can shift the weight to a more optimal balance with diet.

The later girls start their periods, the longer they tend to live. Each year later is associated with significantly lower risk of dying from heart disease and stroke, plateauing out with the lowest overall mortality among those who don’t start menstruating until age 15. Isn’t 15 a little late? It didn’t used to be. A century ago, the age of first menstruation averaged as late as nearly 17. Similarly, the age of breast development has dropped an average of about three months per decade over the last half century around the world––down to nine or 10 years old in the United States, necessitating a change in textbook definitions of “premature” puberty.

Earlier breast development (before age 10, versus 12 or 13) is associated with as much as 23 percent greater breast cancer risk later in life. And each year later a girl starts to menstruate is linked to significantly lower risk of cancers of the uterus, liver, skin, bladder, colon, lung, and breast. Thankfully, the age of puberty is something over which we have a degree of control.

Higher levels of IGF-1 are associated with earlier sexual maturity, so it’s no surprise that girls eating more animal protein experience puberty significantly earlier––an effect not seen with protein from plants. A meta-analysis of 16 studies on diet and development found that one’s first period appears to start earlier by two months for each additional one gram per day of animal protein intake in childhood. So, for example, at seven years old, girls consuming more than 12 servings of meat a week had 75 percent greater odds of menstruating within the next five years or so compared to girls at that age eating less than four servings a week, and this relationship was seen for both red meat and poultry consumption. IGF-1 and other aging pathways may not fully explain these findings, however, as persistent pollutants that build up in meat, like DDT, have also been linked to precocious puberty.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

I mentioned The Enzyme mTOR as an Engine of Aging. 

For more on puberty, see:

For more on fertility, check out:

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