Chapter 5. Hormones and the Brain
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Laura Sanders Taking a pregnancy hormone staves off multiple sclerosis relapses, a small clinical trial suggests. The results hint at a potential therapy for women who suffer from MS, a debilitating disease in which the body’s immune system attacks the insulation that wraps around nerve cell fibers. A curious observation kicked off this line of research: Pregnancy offers a temporary reprieve for women with MS. Since that discovery, in the 1990s, scientists have been testing whether certain pregnancy hormones might combat MS in women who aren’t pregnant. In addition to a standard MS drug, 164 women with MS received either a placebo or estriol, an estrogen made by the placenta that peaks toward the end of pregnancy. After two years, women who received estriol had an average of 0.25 relapses a year, while women who received the placebo had 0.37 relapses a year, UCLA neurologist Rhonda Voskuhl and colleagues write online November 24 in Lancet Neurology. Researchers don’t know whether estriol would have similar effects in men with MS. The results warrant a larger clinical trial, the authors say. An accompanying commentary in the same issue of Lancet Neurology questions the results, though. MS specialist Annette Langer-Gould of Kaiser Permanente in Pasadena, Calif., raises methodological issues and writes that pregnancy comes with a host of changes that could be responsible for protection from MS. © Society for Science & the Public 2000 - 2015.
By Hanae Armitage CHICAGO, ILLINOIS—When prairie voles choose a mate, there’s no turning back—the “love chemical” oxytocin increases in their brains and they devote themselves to only each other. Although scientists have observed the behavioral and chemical side of prairie vole love, the neural networks behind commitment are still a mystery. Now, a group of scientists are working toward clearing up the neuronal backdrop of long-term love, and yesterday, presented their findings here at the annual meeting of the Society for Neuroscience. Studies have long suggested the nucleus accumbens, a part of the brain involved in reward processing, plays a crucial role in this type of devotion. To get a better look at the neuronal activity of this region, the scientists mounted a small-scale microscope that monitors calcium flux on top of a male prairie vole’s head (the more calcium into the neuron, the more neuronal activity). They saw that when male prairie voles interacted with their special lady vole, neuronal activity in the nucleus accumbens jumped 20% compared with when they interacted with a random female. Upon closer inspection, scientists saw that specific neurons that fired when the voles interacted with their mates stayed silent when they interacting with a different female. The result, though preliminary, indicates that mates stimulate the brain’s reward center in ways that nonmates cannot. © 2015 American Association for the Advancement of Science.
Sara Reardon Naked mole rats are among the ugliest creatures in the animal kingdom, and they engage in acts that seem repulsive — such as eating one another’s, and their own, faeces. Now researchers have found one biological motivation for this behaviour. When a queen mole rat’s subordinates feed on her hormone-filled faeces, the resulting oestrogen boost causes the beta rats to take care of the queen’s pups, according to results presented on 18 October at the Society for Neuroscience meeting in Chicago, Illinois. Like bees, naked mole rats live in eusocial colonies, with only one queen rat and a few males that can reproduce. The rest of the colony consists of dozens of infertile subordinates that help with tasks such as foraging and defending the nest. The subordinate rats also take care of the queen’s pups as though the babies were their own: they build the nests, lick the pups and keep them warm with their body heat. Because they have no mature sex organs, subordinate rats cannot produce the hormones that would usually drive parenting behaviour. To look at what generates the rats’ caring ways, animal biologist Akiyuki Watarai and behavioural scientist Takefumi Kikusui at Azabu University in Japan played recordings of crying mole-rat pups to subordinate rats. Animals whose queens had just given birth paid more attention to the crying than those from other groups, suggesting that the pregnancy itself triggered subordinates’ maternal instincts. © 2015 Nature Publishing Group
Susan Milius Bachelor prairie voles can’t tell females of their species apart. Yet the clueless fellows can change, forming pair-bonds for life with the opposite sex and even distinguishing between two female strangers. Bachelors aren’t blind or stupid; they recognize individual males among their fellow short-tailed Microtus ochrogaster rodents scurrying through old fields in the center of North America. And males are certainly interested in the interchangeable females. In lab tests, bachelors claw and bite at cage dividers between the sexes, says Alexander Ophir of Cornell University. Conquering the divide and mating with a female after just six hours of her company can form a lifelong pair-bond between voles. Only about 5 percent of mammal species live this socially monogamous lifestyle, and the voles have played starring roles in studies of the neurobiology of bonding. (Social monogamists, including both voles and some Homo sapiens, don’t entirely forgo extra-pair encounters.) A pair-bonded couple can crowd three litters of young into their roughly six to nine months of life in the wild, Ophir says. One aid to speeding through family life: Females can get pregnant as soon as they give birth. “You sometimes see pups being delivered as males are trying to copulate with the female,” he says. Pair-bonding requires recognizing at least one female. “It’s all well and good to fall in love, but if you don’t know who you fell in love with, it’s worthless,” Ophir says. And paired-up voles can go further. Tests show they notice the difference between two females they have never mated with, Ophir and former student Tomica Blocker report in the October Animal Behaviour. © Society for Science & the Public 2000 - 2015
By Puneet Kollipara The list of health problems that scientists can confidently link to exposure to hormone-disrupting chemicals has grown to include diabetes, cardiovascular disease, and obesity, a new scientific statement suggests. The statement, released today by the Endocrine Society, also adds support to the somewhat controversial idea that even minute doses of these chemicals can interfere with the activity of natural hormones, which play a major role in regulating physiology and behavior. But the report—which updates a similar statement released in 2009—is drawing sharp criticism from the chemical industry. An executive summary of the new statement, which synthesizes 1300 studies on endocrine disrupters, posits that scientists are more confident than ever before in linking these substances to a host of known health issues, including reproductive and developmental problems, thyroid impairment, certain reproductive cancers, and neurodevelopmental problems such as decreased IQ. But studies suggest those links can now be extended to heart and weight problems, and diabetes, says the executive summary's first author, Andrea C. Gore, a professor of pharmacology and toxicology at the University of Texas, Austin. Six years ago, scientists couldn’t make such a strong case for those links, Gore says, because there weren’t enough good studies. “But this has really been an emerging field where there is much stronger evidence now,” Gore told reporters today on a conference call. Still, some toxicologists and industry groups have long disputed the assertion that endocrine disrupters can trigger effects at minimal doses; this idea can be tough to test in lab animals, which are usually exposed to high doses in toxicology studies. © 2015 American Association for the Advancement of Science
Nancy Shute There have been suggestions that low levels of vitamin D might be a factor in cognitive decline and Alzheimer's disease, but there's no proof that the lack of D is actually causing the problems. A study published Monday doesn't prove that link, but it does find that people with low levels of vitamin D lost key thinking skills more quickly than people with enough. The study is notable because of the diversity of the participants: 62 percent were women, 30 percent were African-American, 25 percent Hispanic and 41 percent white. Most earlier studies looking at cognitive decline and vitamin D were in white people. The participants lived in California's Sacramento Valley and were mostly in their 70s when they entered the study. The researchers followed up with them for about five years, having them take annual neurological exams and neuropsychological testing at the University of California, Davis, Alzheimer's Disease Center. Most of the 382 people in the study were low on vitamin D, tested by measuring 25-hydroxyvitamin D in the blood. One-quarter of the participants were deficient in vitamin D, and 35 percent had levels deemed insufficient. That's not a surprise — most older people are below the "adequate" level of 20 to less than 50 ng/ml, often because they're not outside much. And most of the people in the study weren't getting the recommended three servings of dairy foods daily that could help. © 2015 NPR
By Elizabeth Landau Ask a physician what the hormone vasopressin is good for, and she will explain that it regulates the volume of water in your body and also affects blood pressure. But since the 1990s, vasopressin has been a hot topic in a very different field: social behavior. And recently it has emerged as a possible target for treating autism spectrum disorders (ASD), which are characterized by social, behavioral and communication impairments. The research is still in early stages, however, and has yielded more questions than answers. Given that one out of 68 children in the U.S. has an autism spectrum disorder, researchers are scrambling to figure out what in the brain might be related to the symptoms, and how they might design an effective treatment. Vasopressin may be a key player in the disorder. But scientists do not yet know whether too much or too little of the hormone—or perhaps some combination of both—is tied to autism. New clinical trials may yield insights. “I think that the work is exciting and important” says Suma Jacob, who leads an autism research laboratory at the University of Minnesota. “I also think we still have a lot more work to do in this field as a whole.” Previous research has shown that vasopressin, like the hormone oxytocin, is associated with parenting behavior and social bonding, including falling in love. In fact, the two hormones are structurally very similar, and there are receptors in the brain that interact with both of them. But high levels of vasopressin are also associated with anxiety and aggression. Intriguingly, some animal studies have found that higher levels of vasopressin increased aggression specifically in males. © 2015 Scientific American
By Melinda Wenner Moyer As many as four out of every five pregnant women say that they suffer from “pregnancy brain”—deficits in memory and cognitive ability that arise during pregnancy, making women more forgetful and slow-witted. Yet studies on the phenomenon have generally not supported these claims: although some have found evidence of problems on certain types of tasks, others, including a recent paper published by researchers in Utah, have found no signs of cognitive problems at all. Some experts believe that pregnancy brain and its postnatal cousin, “baby brain,” could largely be a product of confirmation bias: pregnant women and new moms expect to experience brain fog and therefore believe they are actually affected. Others argue that the mental symptoms might simply be too difficult to confirm in a laboratory setting. In the most recent study, researchers at Brigham Young University gave cognitive and neuropsychological tests to 21 women in their third trimester of pregnancy and then tested them again six months after they gave birth. They administered the same tests at similar intervals to 21 women who had never been pregnant. They found no differences between the groups no matter when they were tested, including before and after giving birth. These findings mesh with those from a 2003 study, which found that pregnant women did not score differently from nonpregnant women on tests of verbal memory, divided attention and focused attention. “There is variety in the results, but overall most studies suggest there are few to no memory impairments associated with pregnancy,” says Michael Larson, a psychologist at Brigham Young and a co-author of the recent paper. He thinks the reason the myth persists may be that women selectively look for evidence that supports the cultural expectation. © 2015 Scientific American
A placebo can make you feel a little better – and now we know how to boost the effect. Drugs based on hormones that make us more cooperative seem to enhance the placebo effect. The finding could lead to changes in the way some trials are performed. Sometimes a sugar pill can be all you need, even when you know it doesn’t contain any medicine. We’re still not entirely sure why. The brain’s natural painkillers, such as dopamine and opioids, seem to be involved, but other factors may be at work too. Evidence that a compassionate, trustworthy carer can speed recovery suggests that there is also a social dimension to the placebo effect. “This interaction between the patient and care provider seems to be based on a more complex system,” says Luana Colloca at the University of Maryland in Baltimore. Hormones that modulate our social behaviour might play a role. Last year, a team led by Ulrike Bingel of the University Duisburg-Essen in Germany, found that oxytocin – the so-called “cuddle chemical” that is thought to help us trust, bond and form relationships – seems to boost the placebo effect, at least in men. In the study, Bingel’s team applied an inert ointment to the arms of male volunteers. Half of them were told that the cream would reduce the degree of pain caused by the painfully hot stimulus subsequently applied. Men who were told that they were receiving pain relief said that the heat was less painful than those who knew that the cream was inert. When oxytocin was squirted up volunteers’ noses, the men reported being in even less pain. The team didn’t test oxytocin in women. © Copyright Reed Business Information Ltd.
By Esther Landhuis The birth of a child leaves its mark on the brain. Most investigations of these changes have focused on mothers, but scientists have recently begun looking more closely at fathers. Neural circuits that support parental behaviors appear more robust in moms a few weeks after the baby is born, whereas in dads the growth can take several months. A study in Social Neuroscience analyzed 16 dads several weeks after their baby's birth and again a few months later. At each check, the researchers administered a multiple-choice test to check for signs of depression and used MRI to image the brain. Compared with the earlier scans, MRI at three to four months postpartum showed growth in the hypothalamus, amygdala and other regions that regulate emotion, motivation and decision making. Furthermore, dads with more growth in these brain areas were less likely to show depressive symptoms, says first author Pilyoung Kim, who directs the Family and Child Neuroscience Lab at the University of Denver. Although some physiological brain changes are similar in new moms and dads, other changes seem different and could relate to the roles of each parent, says senior author James Swain, a psychiatrist at the University of Michigan (brain diagrams below). A 2014 behavioral study of expectant fathers showed that midpregnancy ultrasound imaging was a “magic moment” in the dads' emerging connection with their baby. Yet the emotional bond was different than it is in expectant moms. Instead of thinking about cuddling or feeding the baby, dads-to-be focused on the future: they imagined saving money for a college fund or walking down the aisle at their daughter's wedding. © 2015 Scientific American
By Sarah Schwartz Researchers have developed a chemical that transforms into a powerful hormone once inside a rat — but only in the brain, not the body. A protein in rats’ brains turns a chemical nicknamed DHED into the hormone estrogen, scientists report July 22 in Science Translational Medicine. This targeted treatment could provide estrogen to the brain and avoid potentially dangerous side effects in the body, the researchers say. “This is an interesting breakthrough,” says neuroendocrinologist Bruce McEwen of the Rockefeller University in New York City. The idea of treatments that affect the brain but not the body, or the body but not the brain, could be useful in treating a number of conditions, including cancer, he says. But the implications of this study for hormone replacement therapy in women is up for debate, a number of researchers say. In menopausal women or those who have had their ovaries surgically removed, lack of estrogen in the brain can cause symptoms such as hot flashes and sleep disturbances. Taking estrogen can relieve those symptoms but can cause side effects in the rest of the body, including an increased risk of certain cancers. The chemical DHED is nearly identical to natural human estrogen, but it has an extra oxygen atom. A specialized protein found in rodents’ brains recognizes the chemical and chops off the oxygen, turning DHED into estrogen. The body’s other organs lack this protein, so they can’t turn DHED into estrogen, says study author Laszlo Prokai, a chemical biologist at the University of North Texas Health Science Center in Fort Worth. © Society for Science & the Public 2000 - 2015.
Helen Shen In April 2011, Robert Froemke and his team were reprogramming the brains of virgin mice with a single hormone injection. Before the treatment, the female mice were largely indifferent to the cries of a distressed baby, and were even known to trample over them. But after an injection of oxytocin, the mice started to respond more like mothers, picking up the mewling pup in their mouths. Froemke, a neuroscientist at New York University's Langone Medical Center in New York City, was monitoring the animals' brains to find out why that happened. At first, the mice showed an irregular smattering of neural impulses when they heard the baby's cries. Then, as the oxytocin kicked in, the signal evolved into a more orderly pattern typical of a maternal brain. The study showed in unusual detail how the hormone changed the behaviour of neurons1. “Oxytocin is helping to transform the brain, to make it respond to those pup calls,” Froemke says. Oxytocin has been of keen interest to neuroscientists since the 1970s, when studies started to show that it could drive maternal behaviour and social attachment in various species. Its involvement in a range of social behaviours2, including monogamy in voles, mother–infant bonding in sheep, and even trust between humans, has earned it a reputation as the 'hug hormone'. “People just concluded it was a bonding molecule, a cuddling hormone, and that's the pervasive view in the popular press,” says Larry Young, a neuroscientist at Emory University in Atlanta, Georgia, who has been studying the molecule since the 1990s. “What we need to start thinking about is the more fundamental role that oxytocin has in the brain.” © 2015 Nature Publishing Group,
Steve Connor Having children can permanently affect the brain of women because the surge in female sex hormones during pregnancy can influence the development of key parts of the central nervous system, a series of studies has shown. The findings suggest that childbirth can affect the female brain, but they could also shed light on the controversy over whether hormone replacement therapy in menopausal women affects the risk of developing Alzheimer’s disease in later life, scientists said. The research looked at two of the oestrogen hormones used to treat the symptoms of menopausal women and found that they could have a complex effect depending on the age of the women and whether or not they had previously given birth. Although the work was mostly carried out on laboratory rats, the scientists said that the findings are more widely applicable to humans because the same hormones and brain cells are involved. The scientists found that the surge in oestrogen hormones during pregnancy, where levels can soar to several hundred times normal levels, can alter “neuroplasticity” or the re-growth of nerve cells in a part of the brain called the hippocampus, which is responsible for aspects of memory and spatial awareness. “Our most recent research show that previous motherhood alters cognition and neuroplasticity in response to hormone therapy, demonstrating that motherhood permanently alters the brain,” said Liisa Galea of the University of British Columbia in Vancouver, Canada.
By John Horgan The New York Times "Sunday Review" section has anointed Richard Friedman its go-to guy for touting behavioral genetics--or "gene-whiz science," as I prefer to call it. In March, Friedman, professor of clinical psychiatry at Weill Cornell Medical College, proclaimed that researchers had discovered a "feel-good gene," which "makes some people inherently less anxious, and more able to forget fearful and unpleasant experiences." As I pointed out on this blog, Friedman's claim—like virtually all reported linkages of complex human traits and disorders to specific genes (see Further Reading)--is based on flimsy, contradictory evidence. I'm so naïve, or arrogant, that I actually thought my critique might dissuade the Times from further hype of gene-whiz science. Times editors must care more about traffic than accuracy, because they devoted almost the entire front page of yesterday’s "Sunday Review" to Friedman's latest travesty, "Infidelity Lurks in Your Genes." The core of Friedman's essay is his assertion that some women are "biologically inclined to wander." More specifically, women who carry variants of the gene AVPR1A—which encodes the receptor for the hormone arginine vasopressin--are "much more likely to engage in 'extra-pair bonding,' the scientific euphemism for sexual infidelity." In support of this claim, Friedman cites a study of Finnish twins and non-twin siblings by a team led by Australian psychologist Brendan Zietsch. The team surveyed the Finnish subjects and found that 9.8 percent of the men and 6.4 percent of the women reported engaging in at least one "extra-pair mating." The researchers found an association between five AVPR1A markers and extra-pair mating in women but not in men.
Richard A. Friedman AMERICANS disapprove of marital infidelity. Ninety-one percent of them find it morally wrong, more than the number that reject polygamy, human cloning or suicide, according to a 2013 Gallup poll. Yet the number of Americans who actually cheat on their partners is rather substantial: Over the past two decades, the rate of infidelity among married men has been pretty constant at around 21 percent, while the percentage of married women who admitted to cheating has mostly hovered between 10 and 15 percent, according to the General Social Survey at the University of Chicago’s independent research organization, NORC. We are accustomed to thinking of sexual infidelity as a symptom of an unhappy relationship, a moral flaw or a sign of deteriorating social values. When I was trained as a psychiatrist we were told to look for various emotional and developmental factors — like a history of unstable relationships or a philandering parent — to explain infidelity. But during my career, many of the questions we asked patients were found to be insufficient because for so much behavior, it turns out that genes, gene expression and hormones matter a lot. Now that even appears to be the case for infidelity. We have long known that men have a genetic, evolutionary impulse to cheat, because that increases the odds of having more of their offspring in the world. But now there is intriguing new research showing that some women, too, are biologically inclined to wander, although not for clear evolutionary benefits. Women who carry certain variants of the vasopressin receptor gene are much more likely to engage in “extra pair bonding,” the scientific euphemism for sexual infidelity. © 2015 The New York Times Company
|By Julie Hecht Unlike porcupines, dogs are a relatively hands-on (actually, paws-on) species, both with one another and with us. YouTube has numerous videos of dogs essentially saying, “Just keep petting me, please. Yes, that’s it…more.” But this relationship is not one-sided. Many studies find that positive interactions between people and dogs can be beneficial for both species. Increases in β-endorphin (beta-endorphin), oxytocin and dopamine—neurochemicals associated with positive feelings and bonding—have been observed in both dogs and people after enjoyable interactions like petting, play and talking. Essentially, interacting with a dog, particularly a known dog, can have some of the same psychophysiological markers as when two emotionally attached people spend time together. But do certain types of interactions have an outsized impact? Dogs are incredibly attentive to human faces and, in some cases, even specific facial expressions. This seemingly routine, benign behavior—your dog turning to gaze on your beautiful face as you do his or hers—could actually hold a very important piece of the puzzle in our relationship with dogs, suggests a study published this week in Science. The new study, by Miho Nagasawa of Azabu University in Japan and colleagues, builds on Nagasawa’s previous work, published in Hormones and Behavior in 2009, that found owners and dogs sharing a long mutual gaze had higher levels of oxytocin in their urine than owners of dogs giving a shorter gaze. (Oxytocin, a humble peptide of nine amino acids that is sometimes called the “cuddle hormone,” has been implicated in social bonding and is instrumental to the cascade of hormonal changes leading up to and following birth.) Nagasawa and her colleagues concluded that their finding was “a manifestation of attachment behavior.” © 2015 Scientific American
By Virginia Morell Like many newborn mammals, baby mice cry to get their mother’s attention. But the mother doesn’t instinctively recognize these calls; she must learn the sounds of her offspring—just as human parents must learn the cries of their infants. Now, a team of researchers has discovered that the hormone oxytocin, which has been tied to trust and maternal bonding, holds the key to how this learning occurs. Only after oxytocin tweaks the brain of a female mouse does she respond with a mother’s concern and attentiveness to crying pups. “It’s an exciting study with implications that … could be helpful to certain disorders, such as autism,” says Larry Young, a neuroscientist at Emory University in Atlanta who was not involved in the work. To understand the role oxytocin plays in a mother mouse’s brain, scientists at New York University School of Medicine first investigated how female mice in general respond to the distress calls of baby mice. Pups emit ultrasonic cries when they are separated from the nest, which sometimes happens when a mother carries her babies to a new location. (Moms change nest locations regularly to elude predators.) When a mother hears these cries, she runs to the lost pup, picks it up, and carries it back to her nest. Other scientists have shown that moms respond even to the distress cries of pups that aren’t their own, readily approaching loudspeakers that broadcast the calls. Most virgin female mice, though, couldn’t care less; they seem completely indifferent to the pups’ cries for help. And yet, some virgin females that have either been housed with a mother and her litter or have been injected with oxytocin will retrieve crying infants. © 2015 American Association for the Advancement of Science.
By Nicholas Weiler Killer whales wouldn’t get far without their old ladies. A 9-year study of orcas summering off the southern tip of Vancouver Island in the Pacific Northwest finds that menopausal females usually lead their families to find salmon, particularly when the fish are scarce. Older females’ years of foraging experience may help their clans survive in years of famine, an evolutionary benefit that could explain why—like humans—female orcas live for decades past their reproductive prime. “Menopause is a really bizarre trait. Evolutionarily it doesn’t make sense,” says biologist Lauren Brent of the University of Exeter in the United Kingdom, who led the new study. Most animals keep having babies until they drop, part of the evolutionary drive to spread their genes as widely as possible. Only female humans, pilot whales, and killer whales are known to go through menopause: At a certain age, they stop reproducing, but continue to lead long, productive lives. Like humans, female killer whales stop giving birth by about 40, but can live into their 90s. Anthropologists have proposed a controversial explanation for menopause in humans: that grandmothers contribute to their genetic legacies by helping their children and grandchildren survive and reproduce. In hunter-gatherer and other societies, elders find extra food, babysit, and remember tribal lore about how to live through floods, famines, and other hardships. According to the “grandmother hypothesis,” this contribution is so valuable that it helped spur the evolution of women’s long postreproductive lives. Orcas too depend on their elders: Adult killer whales’ mortality rates skyrocket after their elderly mothers die. But how the menopausal whales might help their children survive was not clear, Brent says. © 2015 American Association for the Advancement of Science.
by Michael Slezak If you want to counteract the effects of getting drunk, a big dose of the so-called "cuddle-chemical" oxytocin might be the answer. Oxytocin has important roles in sexual behaviour and social bonding, and has previously been investigated as a way to help wean alcoholics off drink. While studying this effect in rats, Michael Bowen from the University of Sydney noticed something strange. Rats that had been given oxytocin didn't seem to get drunk. "Those that had the oxytocin were up and moving about as if they hadn't had any alcohol at all, whereas the ones that didn't have oxytocin were quite heavily sedated," Bowen says. This effect was confirmed in a second experiment, in which half the rats were given an injection of oxytocin straight into the brain, at a level about 150,000 times what would normally be found there. They were then given alcohol, after which researchers tested their motor control and reaction times. Oxytocin seemed to completely counteract the effects of the booze – even when a rat had consumed what would be equivalent to about one and a half bottles of wine in humans. "The rats that had received oxytocin, as well as the alcohol, were virtually indistinguishable from the rats that hadn't received any alcohol at all," says Bowen. This could be thanks to the brain's GABA receptors, where alcohol is thought to exert its intoxicating effects. Bowen's team found that oxytocin was binding to two parts of these receptors, blocking alcohol from getting there. "It was actually preventing alcohol affecting these sites in the brain that make you intoxicated." © Copyright Reed Business Information Ltd
By Anne Harding NEW YORK (Reuters Health) - Reduced sexual activity could cause a dip in testosterone levels in older men, new findings suggest. Among men 70 and older, those who reported a decline in sexual activity and desire over a two-year period also showed small declines in serum testosterone, Dr. David Handelsman of the ANZAC Research Institute at the University of Sydney and Concord Hospital in New South Wales, Australia, and colleagues found. They report their findings in the Journal of Clinical Endocrinology and Metabolism, online January 28. "Decline in serum testosterone is more likely to be the result rather than the cause of sexual dysfunction among older men who don't have reproductive disorders," Dr. Handelsman told Reuters Health by email. "The widely prevalent misinterpretation of this (as if the mild lowering of serum testosterone needs or might benefit from testosterone treatment) is one of the main drivers of the massive over-use of testosterone prescriptions in North America over the last decade." While declines in androgens and sexual function are both thought to be aging-related, Dr. Handelsman and his colleagues note in their report, the relationship between androgen levels and sexual function is not clear. To better understand the temporal and predictive relationship between androgen levels and sexual function, the researchers looked at 1,226 men participating in the Concord Health and Ageing in Men Project (CHAMP), measuring their levels of testosterone, dihydrotestosterone, estradiol, and estrone with liquid chromatography-tandem mass spectrometry. Men also reported on their sexual function using standardized questions, at baseline and two years later. © 2015 Scientific American