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Sperm Works Best in the Winter, Study Finds

Spring may be when a young man’s fancy turns to love, but new evidence suggests that it’s winter when his sperm is at its spunkiest. 

Researchers at Israel’s Ben-Gurion University of the Negev found that sperm concentration and the percentage of fast motility—the ability to move spontaneously and independently—decreased significantly from spring into summer and fall, rebounding in the winter. (Find out how a man produces 1,500 sperm a second.)

sperm picture
Human sperm is seen in an microscopic image. Photograph by Dennis Kunkel, Visuals Unlimited


The physical structure of the sperm cells was also the healthiest in the winter months, according to the study, which tested 6,455 semen samples over the course of three years.

“This study was aimed to explore the possibility that changing weather is somehow related to the quality of sperm, a phenomenon well known from the animal world,” study leader Eliahu Levitas said in an email.

Warm Weather Bad for Sperm?

It’s possible that temperature could play a role in sperm health, just as changes in light have been found to cause sperm variation in some animals.

For instance, “it makes sense that we might see seasonal differences in sperm production, because we know that when the testicles get too hot they work less efficiently,” said Allan Pacey, senior lecturer in andrology—the study of male reproduction—at the University of Sheffield in the U.K., who was not involved in the new study. (Related: “Confirmed: Couch Potatoes Have Lower Sperm Counts.”)

Even so, said Levitas, “the real reasons for a reduced male fertility are in my opinion still [largely] a mystery. We are still searching for the factors that cause variations, even in the fertile male population.”

Fall Baby Booms Explained

Meanwhile, the findings offer a possible explanation for seasonal birth patterns, suggesting that the well-documented phenomenon of high fall birth rates could be tied to seasonal changes in sperm quality. (See “Sperm Tracked in 3D—A First.”)

The researchers cross-referenced their findings with five years of data of the birth registry at Israel’s Soroka University Medical Center. They found that birth rates were highest in the fall, which reflects increased conception rates in the previous winter.

baby picture
Aviva Zigdon holds her baby boy at the Soroka University Medical Center in Beersheba, Israel, in October 2011. Photograph by Ronen Zvulun, Reuters


“We were able to show the connection between the increase in sperm quality and the following increase in deliveries nine months later,” said Levitas, whose study was published in February in the American Journal of Obstetrics & Gynecology.

Conception Rx

While the findings will be of interest for couples trying to conceive, it doesn’t mean people shouldn’t give it the old college try throughout the year—and as often as possible. (Related: “Valentine’s Science—Why Gauging Sexiness Is Sophisticated.”)

“It would be inappropriate to suggest couples only try and conceive in certain seasons, as what is important is that couples have regular sex over the course of the year,” said Pacey.

Who would object to that prescription?


  1. amit ranjan
    April 25, 2013, 6:00 pm

    It is commonly believed that those who are born in winter months are mentally and physically stronger. Those born in summer months are of romantic nature.

  2. JGreg
    April 5, 2013, 11:53 am

    Adelaide, point taken. Please find below a study which may complement all comments above. Yes indeed, there are variations involved as long seasons that we may determine the original subject.
    The study, which will be published this week, was led by scientists at Harvard University and monitored the development of 21,000 boys and girls worldwide. It shows that there were large seasonal variations when it came to weight, length, height, head size and mental ability.
    Researchers believe that the effects on the pregnant mother and the growing foetus of seasonal variations in diet, hormones, temperature, exposure to sunlight and viruses and other infections may influence a baby’s characteristics.
    The American and Australian psychiatrists and anthropologists from Harvard and Queensland universities measured the children and carried out mental and motor tests at birth, at eight months, and at four and seven years.
    Compared to summer births, those born in winter were significantly longer at birth, and were heavier, taller and had larger head circumference at age seven. They also had higher scores in a series of intelligence exercises. By the age of seven, winter- and spring-born children were 210g heavier, 0.19cm taller, and had head circumferences significantly larger than summer and autumn-born children. The results also show that babies born in the winter were the longest, while winter- and spring-borns weighed the most at the age of seven and were also the tallest.
    The researchers, whose work appears this week in the medical journal Schizophrenia Research, conclude: “The overall pattern of findings is that winter/spring babies are both ‘bigger’ on the anthropometric variables and ‘smarter’ on the selected neurocognitive variables.”
    The new study is the latest – and largest – in a series of projects worldwide aimed at evaluating the effect of the seasons on human health, longevity and physical and intellectual development. In 2002, scientists at Germany’s prestigious Max Planck Institute for Demographic Research announced that people born in the autumn live longer than those born in spring, and do not become as ill in old age.
    Studying census data from Denmark, Austria and Australia, the institute also revealed a seasonal link to life expectancy for those older than 50. In Austria, for example, it was found that adults born between October and December lived some seven months longer that those born between April and June.
    Dietary changes and seasonal infections are thought to be at the heart of the phenomenon. “A mother giving birth in spring spends the last phase of her pregnancy in winter, when she will eat fewer vitamins,” said Gabriele Doblhammer, one of the scientists who carried out the research. “When she stops breast-feeding and starts giving her baby normal food, it is in the hot weeks of summer – when babies are prone to infections of the digestive system.”
    The season of birth can also influence whether a person is an optimist or pessimist. Yet it is the summer’s babies that have a brighter outlook than winter-born grumblers.
    The American and Australian researchers offer a number of explanations for such differences in the early years of life. One theory is that foetal exposure to changing seasonal factors such as temperature, rainfall and ultraviolet radiation may be responsible.

  3. kulwinder singh grewal
    March 28, 2013, 5:59 pm

    earth day is coming in april grate.NGM. i love u.

  4. Chudamani Akavaram
    March 28, 2013, 12:11 am

    It is commonly believed that those who are born in winter months are mentally and physically stronger. Those born in summer months are of romantic nature.

  5. Leah Mingxz Ogzz
    March 27, 2013, 2:00 am

    .awesome ! \m/ 😀
    .that’s really COOL ! 🙂

  6. arnex
    March 26, 2013, 4:40 am

    hot or cold weather isn’t the basis of the sperm’s health. , its the basis of the couples’ intercourse rate, they do it more often during cold days…thus increasing the percentage of conception .

  7. kushal
    March 20, 2013, 11:18 pm

    effect of seasonal variations was much anticipated and now its been conformed.

  8. B
    March 20, 2013, 10:11 pm

    Does it really matter? Most men make so many sperm and are fertile at all times. I think the best bet for couples trying to conceive is to be aware of when women ovulate ( egg white stretchy vaginal mucosa) and to definitely have sex at those times. If a man has a low sperm count, or a woman has irregular ovulations then there are other options, such as IVF and fertility medicines. I think a key to pregnancy too, is for both partners to relax with each other and to stop stressing out about getting pregnant. Stress can definitely halt pregnancy!

  9. segun oluwole
    March 19, 2013, 12:59 pm

    what a brilliant finding! Can such a reseach be made in africa, especially in hamattan?

  10. arefine khan
    March 19, 2013, 9:41 am

    i don’t really see that much material to count on. winter, summer – these are relative according to places. in sub-continental areas winters are hotter than some of the polar areas summer , and still population is of huge number.
    Some study tried to prove that child born in winter is better in math than the 1 born in summer or fall. i can see lots of mathematicians born in summer. i am bad in math and i wonder how bad i could be if i was born on some hot day..
    there need more solid evidences to prove sperms or persons – affective or talented. 🙂