We mammals have it rough. Especially the humans among us. All
mammals are born helpless — their survival hinges on maternal
care — but compared to many other species, Homo sapiens require
a prolonged childhood. Raising a human being is no joke.
|The beneficial effects of “the
bonding hormone” on maternal blood pressure are now being
measured. From the collection of U.S. Children’s Bureau
c. 1945. Photo: Georg Jones. Courtesy National Library of Medicine.
Consider the mice of the field. A prairie vole (a critter resembling
a mouse) weans its young at the tender age of 3 weeks or so, when
the youngster departs to seek its fortune. But weaned human tots
can't be cast out, so a lack of maternal bonding can be dire. It
is, to put it mildly, a risk factor.
So, too, is an unhappy marriage.
This is a true-love story. It's about the rapport between mother
and infant. It's also about romantic love — not the kind
that made Romeo and Juliet risk everything, double or nothing,
but rather the contentment they might have found with a longer-term
deal. And it's about how maybe, if we're lucky, we can cultivate
How do scientists analyze the effects of loving care on health?
One way is to look at the role of oxytocin, a pituitary hormone,
and measure its relation to blood pressure and heart rate, as well
as to blood levels of stress hormones.
is produced only in mammals. A peptide hormone which exhibits neurotransmitter-like
actions, it has receptors in various sites, including the cardiovascular
system. In the female body it stimulates the contraction of uterine
muscle and the secretion of milk. Discovered at the turn of the
20th century, it was eventually synthesized in the 1950s and found
clinical uses in labor, delivery and postpartum recovery.
Now Dr. Kathleen Light stands among the first scientists worldwide
to study oxytocin in human social relationships. Funded through
an NIH grant at the University of North Carolina, Chapel Hill,
she recently traveled here to deliver her lecture "Loving Family
Relationships and Oxytocin: New Human Findings."
Light described oxytocin as "the bonding hormone" known to enhance
pair-bonding in the 5 percent of mammals that are monogamous. Humans,
she reminded us, are serially monogamous.
"If you are in love," she explained, "that contact becomes rewarding
because of pathways in the brain activated by oxytocin." So if
you give oxytocin to the females in a monogamous species like prairie
voles, they are more likely to pair-bond with males. (Vasopressin,
a related hormone, works this way on the males.) Oxytocin is also
involved with social recognition and behavior, pain and stress
regulation, mood and affect.
Light noted that there is extensive literature on animals and
oxytocin, but "few studies look at oxytocin in humans, and even
fewer in the context of social relations." There have been human
studies showing that social support is good for you, that marriage
has a salutary effect on health, but these didn't look at oxytocin.
She designed studies using "warm contact" in which couples sit
close together, hips touching, in a love seat. They hold hands,
talk to each other about a happy memory, then hug for 20 seconds.
Light found that the warm contact raised oxytocin blood levels
in both men and women if they had supportive partners. These elevations
were related to a decrease in blood pressure (BP) in women, but
not, she said, in men.
|Le Mari Malade [The Sick Husband]. Lithographic
print by Charles Motte, after A. Maurin, c. 1815. Courtesy
National Library of Medicine.
Study Design Crucial in Couples Work
Studying human subjects can be tricky, since folks
being observed may feel uncomfortable and behave in ways that
are altered by the observation itself. When asked how she designed
her studies, UNC's Dr. Kathleen Light offered these details: "There
are lots of different ways to design the couple studies. We
tried for a naturalistic setting, like couples sitting together
at the movies. We also left the couples alone during their
warm contact period so they would feel comfortable and behave
normally. For the mother/baby interactions, we told the moms
to behave as they usually do at home with their babies. This
is one reason why our findings in the lab are linked to what
happens at home — why how often the couples hug at home
or how often the mom picks up her baby at home is related to
the oxytocin and blood pressure measures we see in the lab
studies. For these initial studies, being naturalistic was
our highest priority. In future studies, we can examine whether
it was the positive verbal interaction or the physical closeness
and warm touch that was the specific component needed to see
Oxytocin levels were also linked to a reduction in women's levels
of the stress hormone norepinephrine but, again, not in men's levels. "This
makes us wonder: is oxytocin a more important regulator of stress
responses in women?" she queried.
Her study couples were no strangers. They were monogamous co-habiting
couples (not necessarily married) who had lived together for more
than one year. Forty percent were African American; the rest were
"The benefit to the women's blood pressure was linked to partner
relationship quality, and to physical affection expressed as frequent
partner hugs," said Light. "Not all marriages are equally advantageous.
It's the relationship quality that determines if marriage has health
benefits over being single."
In a separate study monitoring BP and heart rate, Light found
that warm contact had a positive effect across all race and gender
groups. Men and women benefited equally, and even if the partner
was no longer present, warm contact had an enduring effect.
Asked why she is among the first to study people this way, Light
replied: "Many studies failed because they were trying to find
an oxytocin change in response to a single event. It takes more
than one exposure; it's a cumulative effect of the way supportive
couples habitually interact together and hug each other."
Studying infants and mothers, Light found that mothers whose oxytocin
increased after they held their infants closely showed lasting
positive effects on the moms' blood pressure. Even without the
babies present, the oxytocin's effect on maternal BP endured. She
replicated the study and found that there was a much stronger effect
if the infant was under 5 months.
Looking at prenatally cocaine-exposed versus non-exposed mother/infant
pairs, she found that the cocaine-exposed mothers had lower oxytocin
levels before and after baby contact, held their babies less at
home and ran higher blood pressures. "They also had higher BPs
in the lab except when they were holding their babies," Light noted. "Many
of the mothers were bottle-feeders, but they were different from
other bottle-feeders," she said. When interacting with their infants,
or when separated briefly from them, as well as when exposed to
tape-recorded baby cries or pictures of babies in danger, a second
preliminary study showed that their oxytocin levels were consistently
lower. They were also not as stressed during separation from their
infants, but more stressed and overwhelmed when they listened to
the tape-recorded baby cries, and interestingly, when seeing pictures
of happy babies.
Because their oxytocin levels were relatively low, Light concluded,
holding their babies was less rewarding and separation less aversive.
So why not give people oxytocin to enhance social behavior? "Last
year's article in Nature by M. Kosfeld et al. showed that
inhaled oxytocin in male subjects increased one kind of trusting
behavior," she said, "but remember, oxytocin makes the uterus contract.
And an uncontrolled decrease in blood pressure can be dangerous." She
noted that nasal oxytocin administration approved for use in Germany
may minimize adverse peripheral effects of oxytocin while allowing
it to influence the brain.
But there are other, more hopeful, implications.
"There are implications for the mother-child bond," Light said. "Even
in the cocaine-exposed mothers, the system was not broken. Their
BPs decreased when instructed to hold their babies." Intervention
is possible, she said.