Archive for the ‘testosterone’ Category

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New study suggests that men may actually suffer more when they have influenza because high levels of testosterone can weaken immune response.

For years women have cried “man flu” when men make a fuss over a few sniffles.

But a new study suggests that men may actually suffer more when they are struck down with flu – because high levels of testosterone can weaken their immune response.

The study by Stanford University School of Medicine, examined the reactions of men and women to vaccination against flu.

It found women generally had a stronger antibody response to the jab than men, giving them better protection against the virus.

Men with lower testosterone levels also had a better immune response, more or less equivalent to that of women.

It has long been suggested that men might be more susceptible to bacterial, viral, fungal and parasitic infection than women are.

The study published in the Proceedings of the National Academy of Sciences, found women had higher blood levels of signaling proteins that immune cells pass back and forth, when the body is under threat.

Previous research has found that testosterone has anti-inflammatory properties, suggesting a possible interaction between the male sex hormone and immune response.

Professor of microbiology and immunology Mark Davis said: “This is the first study to show an explicit correlation between testosterone levels, gene expression and immune responsiveness in humans.

“It could be food for thought to all the testosterone-supplement takers out there.”

Scientists said they were left perplexed as why evolution would designed a hormone that enhances classic male sexual characteristics – such as muscle strength, beard growth and risk-taking propensity – yet left them with a weaker immune system.

Previous studies have found that while women may accuse men of exaggerating when they have flu, females who are more likely to admit to having sniffles and sneezes.

The research, carried out by London School of Hygiene and Tropical Medicine last winter, shows that women are are 16 per cent more likely to say they are ill.

http://www.telegraph.co.uk/health/healthnews/10536083/Man-flu-the-truth-that-women-dont-want-to-hear.html

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Despite a known link between a masculine-looking face and aggression in men, macho-faced soldiers didn’t survive Finland’s World War II Winter War in greater numbers than recruits with less masculine faces.

The macho-looking men did, however, have more children in their lifetimes than thinner-faced guys, suggesting that face shape is a sign of evolutionary fitness.

The new findings, published today May 7 in the journal Biology Letters, reveal nuances in how hormones, genetics and societal structures might work together to influence evolution. For example, the technology of 20th-century warfare may have turned survival into a matter of luck rather than evolutionary fitness, said study leader John Loehr, an evolutionary ecologist at the University of Helsinki Lammi Biological Station.

“You have very little individual ability to change your fate,” Loehr told LiveScience. “You’re put in a situation where you and the 20 other people who are in your trench are hit by a shell, and it’s game over.”

High levels of testosterone during development are linked with a certain macho look: a broad face, strong jaw and narrow eyes. Any number of swaggering movie stars, from Paul Newman to Channing Tatum (“G.I. Joe”), has parlayed this face shape into successful onscreen careers.

Meanwhile, psychologists have found that guys with Newman’s squint or Tatum’s wide cheekbones tend to be higher in aggression than men with thinner faces. One study on Japanese baseball players, released in April, found that wider-faced players hit more home runs. And in 2008, Canadian researchers discovered that hockey players with wider faces spent more time in the penalty box than other players for aggressive behavior.

The hockey player finding got Loehr thinking about whether high testosterone (and thus, aggression) might confer a survival advantage on wider-faced guys.

“The obvious thing, for me, was, ‘Well, can we get some military data?'” he said.

Fortunately, he could. Finland is a country with meticulous record-keeping, and at the library for the Finnish National Defense in Helsinki, Loehr inquired of a librarian where he might find resources with photos of World War II soldiers (for facial width measurements) as well as personal data about those men.

“She sort of walked around the corner and there were rows of these books sitting there with all the pictures and an amazing amount of personal data,” Loehr said.

Over several months, Loehr pulled together other resources, including photo books of dead soldiers compiled during Finland’s three-and-a-half-month Winter War with the Soviet Union in 1939. Using these old books, he was able to measure facial widths of both surviving soldiers and men lost during the war. He also knew these men’s ranks and how many children they had during their lifetimes.

Military service was and still is mandatory in Finland, Loehr said, so World War II soldiers were a good representation of the male population.

Loehr focused on three WWII regiments, for a total of 795 soldiers. He and co-researcher Robert O’Hara of the Biodiversity and Climate Research Center in Germany found that wider-faced soldiers fathered more children than narrower-faced ones. The finding would have been expected by evolutionary researchers, given previous studies suggesting that fertile women are drawn to more masculine men.

The other findings were more surprising. For one, the wider-faced guys were actually less likely than narrow-faced men to rank higher in the military hierarchy. In other words, the higher the rank, the more likely the man was to have a narrow face.

“That’s a curious one,” Loehr said. Ecologically, he said, you’d expect the men who fathered more children in a community to be the socially dominant guys.

“For human species, it’s perhaps more nuanced,” Loehr said. For example, wide-faced guys have been shown in laboratory experiments to be less trustworthy. Trustworthiness might be more important for military leaders than dominance or aggression.

Another possibility is that the wider-faced guys could have moved up the military ranks during periods of conflict, Loehr said, as his findings were based on rank before the Winter War started. A study published in June 2012 found that in competitive situations, macho-faced guys are the most likely to work together to defeat a common enemy. If that’s the case, any testosterone advantage may not have come out until war began.

Second, Loehr and O’Hara found that face shape didn’t affect survival at all. A wider-faced man was equally as likely to die in battle as a man with a narrower face.

Technology may trump testosterone, Loehr said. One study, published in 2012 in the journal Evolution and Human Behavior, found that in fights involving hand-to-hand combat or other physical contact, narrow-faced men were more likely to die than wide-faced men. In conflicts where a gun, poison or other remote weapon was used, face shape made no difference.

The same could be true for Finnish soldiers, who fought and died with guns in the trenches, Loehr said.

“You would think that thousands of years ago, when combat would have been more hand-to-hand, without much use of tools, that you would have a different result,” he said. “It’s possible that humans have changed how selection can operate by developing this technology.”

http://www.livescience.com/29393-macho-faces-war-survival.html

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From a strictly Darwinian viewpoint, homosexuality shouldn’t still be around. It isn’t the best way to pass along one’s genes, and to complicate the picture further, no “gay genes” have even been identified. According to a newly released hypothesis, the explanation may not lie in DNA itself. Instead, as an embryo develops, sex-related genes are turned on and off in response to fluctuating levels of hormones in the womb, produced by both mother and child. This tug of war benefits the unborn child, keeping male or female development on a steady course even amid spikes in hormones. But if these so-called epigenetic changes persist once the child is born and has children of its own, some of those offspring may be homosexual, the study proposes.

Evolutionary geneticist William Rice of the University of California, Santa Barbara, felt there had to be a reason why homosexuality didn’t just fade away down the generations. Research estimates that about 8% of the population is gay, and homosexuality is known to run in families. If one of a set of identical twins is gay, there’s a 20% probability that the other will be, too.

Furthermore, Rice notes, “homosexuality isn’t just a human thing.” Among California gulls, which he watches from his office window, about 14% of pairs are female-female. In Australian black swans, some 6% of pairs are male-male, and 8% of male sheep are attracted exclusively to male partners.

But many genetic screens have failed to turn up genes that are responsible for sexual orientation. So to find out what makes homosexuality persist, Rice and colleagues began a comprehensive survey of the literature.

According to conventional wisdom, an embryo becomes a boy when a gene on the Y chromosome triggers the development of testes, which then begin to produce male sex hormones, including testosterone, at about the 8th week of gestation. With no Y chromosome and hence no testosterone, the embryo becomes a girl.

But testosterone doesn’t explain everything, the researchers found. For one thing, female fetuses are exposed to small amounts of the hormone from their adrenal glands, the placenta, and the mother’s endocrine system. At many key points of gestation, male and female fetuses are often exposed to similar amounts of testosterone. Levels of the hormone can even be higher than normal in females and lower than normal in males without any effect on genital or brain structure.

Rice and his co-workers were more intrigued by studies showing that male and female fetuses respond differently to the hormones that surround them, even when one hormone is temporarily higher. In their study, published online today in The Quarterly Review of Biology, the authors propose that differences in sensitivity to sex hormones result from “epigenetic” changes. These are changes that affect not the structure of a gene but when, if, and how much of it is activated—by chemically altering a gene’s promoter region or “on” switch, for example. Epigenetic changes at key points in the pathway through which testosterone exerts its effects on the fetus could blunt or enhance the hormone’s activity as needed, the authors suggest.

Although epigenetic changes are usually temporary, they involve alterations in the proteins that bind together the long strands of DNA. Thus, they can sometimes be handed down to offspring. According to the hypothesis, homosexuality may be a carry-over from one’s parents’ own prenatal resistance to the hormones of the opposite sex. The “epi-marks” that adjusted parental genes to resist excess testosterone, for example, may alter gene activation in areas of the child’s brain involved in sexual attraction and preference. “These epigenetic changes protect mom and dad during their own early development,” Rice says. The initial benefit to the parents may explain why the trait of homosexuality persists throughout evolution, he says.

“The authors have done a terrific job providing a mechanism for genetic variation, especially a variation that might not be expected to persist because it’s so tightly bound to reproduction,” says evolutionary biologist Marlene Zuk of the University of Minnesota, Twin Cities. But she adds that to go from changes in gene expression to why someone is attracted to a person of the same sex is a question for which science may never fill in all the blanks.

http://news.sciencemag.org/sciencenow/2012/12/homosexuality-may-start-in-the-w.html?ref=hp

Talk about a longevity strategy no man wants to pursue. A recent study published in the journal Current Biology finds that Korean eunuchs — castrated men — lived 14 to 19 years longer than other men, suggesting that male sex hormones play a role in life span.

In the study, the researchers used a genealogy record called the Yang-Se-Gye-Bo that tracked eunuchs who worked in the Korean imperial court during the Chosun Dynasty, which ruled from the 14th to early 20th centuries.

Researchers were able to identify 81 eunuchs, who were castrated as boys, and determined that they lived to an average age of 70, significantly longer than other men of similar social status. Even kings didn’t typically make it to age 50.

Three of the 81 eunuchs lived to 100, a centenarian rate that’s far higher than would be expected in modern society. The current incidence of centenarians is 1 per 3,500 people in Japan, and 1 per 4,400 people in the United States, for instance; thus, the incidence of centenarians among Korean eunuchs was at least 130 times higher than that of present-day developed countries, according to the paper.

TIME.com: Want to live longer? Don’t try caloric restriction

“Our study supports the idea that male sex hormones decrease the lifespan of men,” the authors write.

Based on earlier research, the authors argue that one explanation for this could be that male sex hormones may negatively influence the immune system and “predispose men to adverse cardiovascular attacks.” They note further that the theory helps explain why females — in many species — live longer than males.

But while animal studies have suggested that castration (which removes the testes, the source of male hormones) results in longer lives, studies in humans have been spotty. In one study of castrati singers, there was no difference in lifespan between them and non-castrated singers; in another study of institutionalized, mentally ill men, however, those who were castrated lived some 14 years longer than those who weren’t.

And there are other reasons that women may outlive men, including for example the presence of estrogen, which may help enhance longevity. Also, as ABC News reports:

“Females may have an advantage in longevity because they have a back-up X chromosome, (Dr. L. Stephen Coles, a co-founder of the Los Angeles Gerontology Research Group,) said. A woman’s body is a mixture of cells, half containing an active X chromosome from her mother and the other half from her father, he said. If there is a defect on one X chromosome, half of her cells will be unaffected.”

TIME.com: Health checkup: How to live 100 years

Further, the longevity of the Korean eunuchs could be attributable to lifestyle factors the study didn’t track, like diet, exercise and stress.

The authors think the men’s long lives can’t be chalked up solely to a privileged lifestyle, however. “Except for a few eunuchs, most lived outside the palace and spent time inside the palace only when they were on duty,” study author Kyung-Jin Min of Inha University told Reuters. Meanwhile, they still tended to outlive other royalty who spent their whole lives inside the palace.

Obviously, the study authors don’t advocate becoming a eunuch. There are more sensible and reliable ways to up your chances of a long, healthy life: don’t smoke, eat a healthy diet, get plenty of exercise.

“For better health and longevity, stay away from stresses and learn what you can from women,” the authors said in a statement.

http://www.cnn.com/2012/09/25/health/eunuchs-lifespan/index.html?hpt=hp_bn12