Autumn is the time of year most associated with bumper crops
of new babies, and that may be because human sperm are generally at their
healthiest in winter and early spring, according to a new study from Israel.
Based on samples from more than 6 000 men treated for
infertility, researchers found sperm in greater numbers, with faster swimming
speeds and fewer abnormalities in semen made during the winter, with a steady
decline in quality from spring onward.
Dr Edmund Sabanegh, an urologist who was not involved with
the new research, said previous studies, mostly in animals, have found similar
results, in line with those species' breeding seasons.
"The hard part of this is really sorting out what
factor is accounting for this," said Sabanegh, the chairman of the urology
department at Ohio's Cleveland Clinic.
The Israeli team, led by Dr Eliahu Levitas from Ben-Gurion
University of the Negev in Beer-Sheva, writes in the American Journal of
Obstetrics & Gynecology that despite the evidence in animals, it remained
unclear whether human sperm is also healthiest during certain times of the
If there is a seasonal pattern, they point out, that
knowledge "may be of paramount importance, especially in couples with
male-related infertility struggling with unsuccessful and prolonged fertility
Knowing when to focus their efforts for the best chances of
conception could spare couples frustration and save them money, the report
How the study was
For the new study, Levitas and his colleagues collected and
analyzed 6 455 semen samples from men at their fertility clinic between January
2006 and July 2009. Of those, 4 960 were found to have normal sperm production,
and 1 495 had abnormal production, such as low sperm counts. The World Health
Organization defines anything over 15 million sperm per milliliter of semen as
a normal sperm count.
Taking into account the approximately 70 days it takes for
the body to produce a sperm cell, the researchers found that men with normal
sperm production had the healthiest sperm in the winter.
For example, those men produced about 70 million sperm per
milliliter of semen during the winter. About 5% of those sperm had
"fast" motility, or swimming speed, which improves a couple's chance
of getting pregnant.
That compared to the approximately 68 million sperm per
milliliter the men produced in the spring, of which only about 3% were
For men with abnormal sperm production, however, the pattern
didn't hold. Those men showed a slight trend toward better motility during the
fall and made the largest percentage of normal shaped sperm - about 7% - during
What the study found
"Based on our results the (normal) semen will perform
better in winter, whereas infertility cases related to low sperm counts should
be encouraged to choose spring and fall," write the researchers, who were
not available to comment before deadline.
But Sabanegh said he doesn't think doctors will start
telling men with low sperm counts to wait until the winter or spring to try to
conceive a child.
"We would continue to encourage them to try regardless
of the season, and they may benefit from interventions or treatments," he
In animal studies, seasonal changes in sperm production and
fertility have been linked to factors ranging from temperature, to length of
daylight exposure and hormone variations.
Among people, previous research has found that sperm counts
around the world are falling. While no one knows why, theories range from a
more sedentary lifestyle to chemicals in the environment that affect sperm
Sabanegh said that researchers need to do more work to find
out why there might be a link between time of year and sperm health.
"It's becoming more certain that our fertility is
seasonal and affected by complex things in our environment that change
it," he said.