Research from Indiana University has found that
sexual activity triggers physiological changes in
the body that increase a woman’s chances of getting
pregnant, even outside the window of ovulation.
The results could eventually influence
recommendations regarding how often to engage in
sexual intercourse for couples trying to get
pregnant. It could also potentially impact treatment
for people with autoimmune disorders.
The conclusions are reported in papers recently
published in the journal Fertility and Sterility and
the journal Physiology and Behavior.
The lead author on both papers is Tierney Lorenz, a
visiting research scientist at the Kinsey Institute.
Julia R. Heiman, a professor in the Department of
Psychological and Brain Sciences and former director
of the Kinsey Institute, and Gregory E. Demas, a
professor in the Department of Biology, are also
co-authors on the study.
All three researchers are also affiliated with the
Center for Integrative Study of Animal Behavior at
IU Bloomington.
"It's a common recommendation that partners trying
to have a baby should engage in regular intercourse
to increase the woman’s changes of getting pregnant
-- even during so-called 'non-fertile' periods --
although it’s unclear how this works," Lorenz said.
"This research is the first to show that the sexual
activity may cause the body to promote types of
immunity that support conception.
"It’s a new answer to an old riddle: How does sex
that doesn’t happen during the fertile window still
improve fertility?"
A few earlier studies show changes in immune
function during pregnancy and after childbirth and
changes in immunity across the menstrual cycle.
But the IU research is the first to show that sexual
activity plays a role in these changes with clear
differences found in immune system regulation in
women who are sexually active versus women who are
sexually abstinent.
The results are based upon information from
participants in the Kinsey Institute's WISH Study
Women, Immunity and Sexual Health which collected
data across the menstrual cycle in 30 healthy women,
about half of whom were sexually active and half of
whom were sexually abstinent. Heiman and Demas are
co-investigators on the study.
In the first paper, Lorenz and colleagues report
sexually active women experienced greater changes in
helper T cells, and the proteins that T cells use to
communicate. In the second paper, they report
differences in antibody levels between the two
groups.
Helper T cells manage the body's immune response in
part by activating the cells that destroy invading
microbes in the body. The antibodies -- also known
as immunoglobulins -- are secreted by white blood
cells and play an important role fighting off
foreign invaders in the body.
"The female body needs to navigate a tricky
dilemma," Lorenz said. "In order to protect itself,
the body needs to defend against foreign invaders.
But if it applies that logic to sperm or a fetus,
then pregnancy can’t occur. The shifts in immunity
that women experience may be a response to this
problem."
There are several types of helper T cells and
immunoglobulins. Type 1 helper T cells assist the
body with defense against outside threats. Type 2
helper T cells help the body accept those aspects of
pregnancy the body may otherwise interpret as
"foreign invaders," such the presence of sperm or
emerging embryo.
Similarly, immunoglobulin A antibodies -- typically
found in the mucous of the female reproductive tract
-- can interfere with the movement of sperm and
other aspects of fertilization. Immunoglobulin G
antibodies -- typically found in the blood -- fight
disease without interfering with the uterus.
Lorenz and colleagues found significantly higher
levels of type 2 helper T cells in sexually active,
non-pregnant women during the luteal phase of the
menstrual cycle, a period when the uterine lining
thickens in preparation for pregnancy. Higher levels
of type 1 helper t cells were found these same women
during the follicular phase in the menstrual cycle,
a period when the ovaries’ follicles are maturing.
They also found sexually active women experienced
similar changes in immunoglobulins, with higher
levels of immunoglobulin G during the luteal phase
and higher levels of immunoglobulin A during the
follicular phase.
Neither shifts in immunity were observed in the
sexually abstinent women.
"We're actually seeing the immune system responding
to a social behavior: sexual activity," Lorenz said.
"The sexually active women's immune systems were
preparing in advance to the mere possibility of
pregnancy."
Both studies contribute to a growing body of
evidence that the immune system isn't a passive
system that waits to react to outside threats, but a
highly proactive system that changes in response to
external cues, such as the physical environment and
social behavior.
The studies may also shed light on previous research
that found unexplained fluctuations in immune
response in women. A recognition that sexual
activity can cause natural fluctuations in blood
tests results could be useful to physicians treating
patients with immune disorders, Lorenz said.
For more information
Fertility and Sterility
Sexual activity modulates shifts in TH1/TH2 cytokine
profile across the menstrual cycle: an observational
study
Link...
Physiology and Behavior
Interaction of menstrual cycle phase and sexual
activity predicts mucosal and systemic humoral
immunity in healthy women
Link...
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