Archive for the ‘Hormomes’ Category

Myostatin (MSTN) is a transforming growth factor-ß (TGF-ß) family member that plays a critical role in regulating skeletal muscle mass [1]. Mice engineered to carry a deletion of the Mstn gene have about a doubling of skeletal muscle mass throughout the body as a result of a combination of muscle fiber hyperplasia and hypertrophy [2]. Moreover, loss of myostatin activity resulting either from postnatal inactivation of the Mstn gene [3], [4] or following administration of various myostatin inhibitors to wild type adult mice [5][7] can also lead to significant muscle growth. Hence, myostatin appears to play as least two distinct roles, one to regulate the number of muscle fibers that are formed during development and a second to regulate growth of muscle fibers postnatally. The function of myostatin appears to have been conserved across species, as inactivating mutations in the myostatin gene have been demonstrated to cause increased muscling in cattle [8][11] , sheep [12], dogs [13] and humans [14]. As a result, there has been considerable effort directed at developing strategies to modulate myostatin activity in clinical settings where enhancing muscle growth may be beneficial. In this regard, loss of myostatin activity has been demonstrated to improve muscle mass and function in dystrophic mice [15][17] and to have beneficial effects on fat and glucose metabolism in mouse models of obesity and type II diabetes [18].

Myostatin is synthesized as a precursor protein that undergoes proteolytic processing to generate an N-terminal propeptide and a C-terminal dimer, which is the biologically active species. Following proteolytic processing, the propeptide remains bound to the C-terminal dimer and maintains it in an inactive, latent complex [6], [19], [20], which represents one of the major forms of myostatin that circulates in the blood [21], [22]. In addition to the propeptide, other binding proteins are capable of regulating myostatin activity in vitro, including follistatin [19], [21], FLRG [22], and Gasp-1 [23]. We previously showed that follistatin can also block myostatin activity in vivo; specifically, we showed that follistatin can ameliorate the cachexia induced by high level expression of myostatin in nude mice [21] and that transgenic mice expressing follistatin in muscle have dramatic increases in muscle mass [19]. Here, I show that overexpression of follistatin can also cause substantial muscle growth in mice lacking myostatin, demonstrating that other TGF-ß related ligands normally cooperate with myostatin to suppress muscle growth and that the capacity for enhancing muscle growth by targeting this signaling pathway is much larger than previously appreciated.

Results

Increased muscle mass in transgenic mice expressing FLRG

Previous studies have identified several proteins that are normally found in a complex with myostatin in the blood [22], [23]. One of these is the follistatin related protein, FLRG, which has been demonstrated to be capable of inhibiting myostatin activity in vitro. To determine whether FLRG can also inhibit myostatin activity in vivo, I generated a construct in which the FLRG coding sequence was placed downstream of a myosin light chain promoter/enhancer. From pronuclear injections of this construct, a total of four transgenic mouse lines (Z111A, Z111B, Z116A, and Z116B) were obtained containing independently segregating insertion sites. Each of these four transgenic lines was backcrossed at least 6 times to C57 BL/6 mice prior to analysis in order to control for genetic background effects. Northern analysis revealed that in three of these lines the transgene was expressed in skeletal muscles but not in any of the non-skeletal muscle tissues examined (Figure 1); in the fourth line, Z111B, the expression of the transgene was below the level of detection in these blots. As shown in Table 1, all four lines exhibited significant increases in muscle weights compared to wild type control mice. These increases were observed in all four muscles that were examined as well as in both sexes. Moreover, the rank order of magnitude of these increases correlated with the rank order of expression levels of the transgene; in the highest-expressing line, Z116A, muscle weights were increased by 57–81% in females and 87–116% in males compared to wild type mice. Hence, FLRG is capable of increasing muscle growth in a dose-dependent manner when expressed as a transgene in skeletal muscle.

The research was funded by grants from the NIH and the Muscular Dystrophy Association and by a gift from Merck Research Laboratories.

See http://www.jhu.edu/sejinlee/%20for%20more%20information for more information.
Citation: Lee S-J (2007) Quadrupling Muscle Mass in Mice by Targeting TGF-ß Signaling Pathways. PLoS ONE 2(8): e789. doi:10.1371/journal.pone.0000789

LINK TO THE PUBLISHED ARTICLE http://www.plosone.org/doi/pone.0000789

Source: Nick Zagorski
Johns Hopkins Medical Institutions

The majority of non-medical anabolic-androgenic steroid (AAS) users are not cheating athletes or risk-taking teenagers. According to a recent survey, containing the largest sample to date and published in the online open access publication, Journal of the International Society of Sports Nutrition, the typical male user is about 30 years old, well-educated, and earning an above-average income in a white-collar occupation. The majority did not use steroids during adolescence and were not motivated by athletic competition or sports performance.

The study, conducted by a collaboration of researchers from around the country coordinated by Jason Cohen, Psy.D. candidate, used a web-based survey of nearly 2,000 US males. Whereas athletes are tempted to take anabolic steroids to improve sports performance, the study suggests that physical self-improvement motivates the unrecognized majority of non-medical AAS users who particularly want to increase muscle mass, strength, and physical attractiveness. Other significant but less highly ranked factors included increased confidence, decreased fat, improved mood and attraction of sexual partners.

Although often considered similar to abusers of narcotics and other illicit drugs (e.g., heroin or cocaine), non-medical AAS users are remarkably different. These users follow carefully planned drug regimens in conjunction with a healthy diet, ancillary drugs and exercise. As opposed to the spontaneous and haphazard approach seen in abusers of psychotropic drugs, everything is strategically planned to maximize benefits and minimize harm. “This is simply not a style or pattern of use we typically see when we examine substance abuse” said Jack Darkes, Ph.D., one of the authors. “The notions of spontaneous drug seeking and loss of control do not apply to the vast majority of AAS users,” added co-author Daniel Gwartney, M.D.

“These findings question commonly held views of typical AAS users and their underlying motivations,” said Rick Collins, one of the study’s authors. “The focus on ‘cheating’ athletes and at risk youth has led to irrelevant policy as it relates to the predominant group of non-medical AAS users. The vast majority of AAS users are not athletes and hence, are not likely to view themselves as cheaters. The targeting of athletes through drug testing and other adolescent or sports-based interventions has no bearing on non-competitive adult users.” The study concludes that these AAS users are a driven and ambitious group dedicated to gym attendance, diet, occupational goals and educational attainment. “The users we surveyed consider that they are using directed drug technology as one part of a strategy for physical self-improvement within a health-centered lifestyle,” said Collins. “Effective public policy should begin by accurately identifying who’s using steroids and why. We hope our research – the largest adult survey of non-medical AAS use we know of – is a significant step forward in that direction.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Charlotte Webber
BioMed Central

Article:
A League of Their Own: Demographics, Motivations and Patterns of Use of 1,955 Male Adult Non-Medical Anabolic Steroid Users in the United States
Jason Cohen, Rick Collins, Jack Darkes and Dan Gwartney
Journal of the International Society of Sports Nutrition (in press)

During embargo, article available at: http://www.jissn.com/imedia/1374735248154681_article.pdf?random=454689

After the embargo, article available from the journal website at: http://www.jissn.com

When it comes to coaching, the pep talk is better than the locker room tirade, University of Florida researchers have found.In a project that applied methods previously used only in classroom settings, a team headed by Professor Robert Singer found that changing people’s attributions, or how they think about themselves, influenced their performance in sports tasks they sought to learn.

“How we think about how we will do and how we’ve just done can very much affect our persistence, our attitudes and our achievements,” said Singer, chair of UF’s department of exercise and sport sciences. “It’s not only a belief in what you can do, it’s also an understanding of thinking more objectively.”

The technique is known as attribution training, which involves using people’s self-perceptions and the extent to which they feel they can control their own behavior to help them succeed at various tasks. Those who believe they can control and change how they feel about themselves are said to have constructive attributions.

In the study, scheduled to be published in March in The Sport Psychologist, Singer and UF colleague Iris Orbach divided 35 college-age beginning tennis players into three groups, each of which was given different instructions regarding personal failure. The first was told they could control their attributions and effort and could change their performance. The second was told their failures were due to a lack of innate ability. The third group was told nothing.

In four trials, the first group scored consistently better in performance, expectation, success perception and emotional control, Singer said. For example, on a test to measure feelings of personal control over behavior, the first group scored twice as high as the control group, while the second group scored below the control group.

In a related study in 1997 that focused on basketball time trials, the first group improved their final time between the first and fourth trials more than twice as much as the control group and more than nine times as much as the second group did.

“When it comes down to it, the primary thing is that you really have to understand what helps you to achieve and what’s under your control,” Singer said. “What has been observed is that those individuals who tend to have more constructive attributions tend to persist longer and tend to achieve more than those who do not have constructive attributions.”

Most studies associated with attribution training techniques have been conducted in the area of education, with the goal of raising the standards for children who are underachievers in the classroom. Singer and Orbach were among the first in the world to apply the techniques to sports.

“Why not try this in a sports setting?” Singer said. “The typical design is to train one group with an attributional orientation that reflects that if you try harder and you try smarter, you’ll have a greater chance of doing well. You’ll learn the skills better and think better things will happen.”

Although it is a common perception that believing in yourself can lead you to success, Singer said his study could have a significant impact on the way people teach and learn athletic activities.

“A lot of times in sports, there’s a negative attitude and a lot of criticism that goes on,” he said. “Probably many athletes and coaches don’t realize the significance of what we’re talking about and the relevance of how people think … I believe that if there’s a better understanding by coaches as to the kind of feedback they give to athletes and how stuff is delivered to them, it could make a difference.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Kristin Harmel
University of Florida

Use of growth hormone to boost athletic performance can lead to diabetes, reports a study published ahead of print in the British Journal of Sports Medicine.

The study reports the case of a 36 year old professional body-builder who required emergency care for chest pain.

He had lost 40 kg in 12 months, during which he had also experienced excessive urination, thirst, and appetite.

He admitted to using anabolic steroids for 15 years and artificial growth hormone for the past three. He had also taken insulin, a year after starting on the growth hormone.

This was done to counter the effects of high blood sugar, but he had stopped taking it after a couple of episodes of acute low blood sugar (hypoglycaemia) while at the gym.

Tests revealed that his liver was inflamed, his kidneys were enlarged and that he had very high blood sugar. He was also dehydrated, and diagnosed with diabetes.

He was given intravenous fluids and gradually increasing amounts of insulin over five days, after which he was discharged. His symptoms completely cleared up, and he was no longer diabetic.

The use of growth hormone has steadily risen among amateur athletes and bodybuilders all round the world, say the authors, because it is easy to buy online and difficult to detect in screening tests—unlike anabolic steroids.

The authors believe that this is the first reported case of diabetes associated with the use of high dose growth hormone, and urge anyone taking high doses to regularly check their blood sugar levels.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Emma Dickinson
BMJ Specialty Journals

Female athletes often lose their menstrual cycle when training strenuously, but researchers have long speculated on whether this infertility was due to low body fat, low weight or exercise itself. Now, researchers have shown that the cause of athletic amenorrhea is more likely a negative energy balance caused by increasing exercise without increasing food intake.”A growing proportion of women are susceptible to losing their menstrual cycle when exercising strenuously,” says Dr. Nancy I. Williams, assistant professor of kineseology and physiology at Penn State. “If women go six to 12 months without having a menstrual cycle, they could show bone loss. Bone densities in some long distance runners who have gone for a prolonged time period without having normal menstrual cycles can be very low.”

In studies done with monkeys, which show menstrual cyclicity much like women, researchers showed that low energy availability associated with strenuous exercise training plays an important role in causing exercise-induced amenorrhea. These researchers, working at the University of Pittsburgh, published findings in the Journal of Clinical Endocrinology and Metabolism showing that exercise-induced amenorrhea was reversible in the monkeys by increasing food intake while the monkeys still exercised.

Williams worked with Judy L. Cameron, associate professor of psychiatry and cell biology and physiology at the University of Pittsburgh. Dana L. Helmreich and David B. Parfitt, then graduate students, and Anne Caston-Balderrama, at that time a post-doctoral fellow at the University of Pittsburgh, were also part of the research team. The researchers decided to look at an animal model to understand the causes of exercise-induced amenorrhea because it is difficult to closely control factors, such as eating habits and exercise, when studying humans. They chose cynomolgus monkeys because, like humans, they have a menstrual cycle of 28 days, ovulate in mid-cycle and show monthly periods of menses.

“It is difficult to obtain rigorous control in human studies, short of locking people up,” says Williams.

Previous cross-sectional studies and short-term studies in humans had shown a correlation between changes in energy availability and changes in the menstrual cycle, but those studies were not definitive.

There was also some indication that metabolic states experienced by strenuously exercising women were similar to those in chronically calorie restricted people. However, whether the increased energy utilization which occurs with exercise or some other effect of exercise caused exercise-induced reproductive dysfunction was unknown.

“The idea that exercise or something about exercise is harmful to females was not definitively ruled out,” says Williams. “That exercise itself is harmful would be a dangerous message to put out there. We needed to look at what it was about exercise that caused amenorrhea, what it was that suppresses ovulation. To do that, we needed a carefully controlled study.”

After the researchers monitored normal menstrual cycles in eight monkeys for a few months, they trained the monkeys to run on treadmills, slowly increasing their daily training schedule to about six miles per day. Throughout the training period the amount of food provided remained the standard amount for a normal 4.5 to 7.5 pound monkey, although the researchers note that some monkeys did not finish all of their food all of the time.

The researchers found that during the study “there were no significant changes in body weight or caloric intake over the course of training and the development of amenorrhea.” While body weight did not change, there were indications of an adaptation in energy expenditure. That is, the monkeys’ metabolic hormones also changed, with a 20 percent drop in circulating thyroid hormone, suggesting that the suppression of ovulation is more closely related to negative energy balance than to a decrease in body weight.

To seal the conclusion that a negative energy balance was the key to exercise-induced amenorrhea, the researchers took four of the previous eight monkeys and, while keeping them on the same exercise program, provided them with more food than they were used to. All the monkeys eventually resumed normal menstrual cycles. However, those monkeys who increased their food consumption most rapidly and consumed the most additional food, resumed ovulation within as little as 12 to 16 days while those who increased their caloric intake more slowly, took almost two months to resume ovulation.

Williams is now conducting studies on women who agree to exercise and eat according to a prescribed regimen for four to six months. She is concerned because recreational exercisers have the first signs of ovulatory suppression and may easily be thrust into amenorrhea if energy availability declines. Many women that exercise also restrict their calories, consciously or unconsciously.

“Our goal is to test whether practical guidelines can be developed regarding the optimal balance between calories of food taken in and calories expended through exercise in order to maintain ovulation and regular menstrual cycles,” says Williams. “This would then ensure that estrogen levels were also maintained at healthy levels. This is important because estrogen is a key hormone in the body for many physiological systems, influencing bone strength and cardiovascular health, not just reproduction.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: A’ndrea Elyse Messer
Penn State

Women who undertake a long-term weight training program produce more biologically active growth hormone, a finding that allows physiologists to understand why weight training improves muscle tone and optimizes metabolic function.A study published in the December issue of the American Journal of Physiology-Endocrinology and Metabolism looked at different forms of growth hormone, used different testing methods, and varied weight training regimens. The research found that the role of growth hormone in women’s muscle development may be more complicated than previously thought.

“We found that growth hormone was responsive to moderate and heavy exercise regimens having 3-12 repetitions with varying weight loading,” said the study’s principal author, William J. Kraemer. “Women need to have heavy loading cycle or workout in their resistance training routines, as it helps to build muscle and bone.”

The study, “Chronic resistance training in women potentiates growth hormone in vivo bioactivity: characterization of molecular mass variants,” was carried out by Kraemer, Jeff S. Volek, Barry A. Spiering and Carl M. Maresh of the University of Connecticut, Storrs; Bradley C. Nindl, U.S Army Research Institute of Environmental Medicine, Natick, Mass.; James O. Marx, The University of Pennsylvania, Philadelphia; Lincoln A. Gotshalk, University of Hawaii at Hilo; Jill A. Bush, University of Houston, Texas; and Jill R. Welsch, Andrea M. Mastro and Wesley C. Hymer, The Pennsylvania State University, University Park, Penn. The The American Physiological Society published the study.

Hormone comes in different formsGrowth hormone, produced in the pituitary, plays an important role in bone and muscle development, particularly in women. Men, on the other hand, rely to a greater extent on muscle-building testosterone. Since women rely on growth hormone to increase muscle and bone strength, the more growth hormone stimulated by a type of exercise, the better its outcome. Growth hormone also plays a role in fighting tissue breakdown, staving off stress fractures and improving metabolic function.

The growth hormone molecule is composed of 191 amino acids, but sometimes the molecules break apart to form smaller pieces. Other times these smaller pieces join together into larger pieces, including pieces that are larger than the original molecule. In addition, growth hormone can attach to binding proteins. It has been shown that there are more than 100 variants of the growth hormone molecule.

This study looked at growth hormone variants using two different tests that measured an immune response, known as immunoassays. Immunoassays are the tests physiologists have traditionally used in such studies. The researchers added a third test, the tibia line rat growth assay, to detect the biological action of the hormones, a novel approach to the study of growth hormones in exercise.

Type of growth hormone varies with exerciseThe researchers divided the participants into two groups: an upper body training group and a total body training group. The two groups were then subdivided: Half used heavier weights with fewer repetitions (up to eight) while the other half used lighter weights with a greater number of repetitions (up to 12).

The researchers took blood samples before and after the initial training (acute exercise) session that all participants did as the start of the study. They also obtained blood samples before and after the final training session 24 weeks later (chronic exercise). One of the unique aspects of the study was that it continued over a relatively long time.

The researchers made these findings:

  • The presence of growth hormone varied with the training regimen.
  • The presence of growth hormone varied with the test used to detect it. This suggests that pituitary function and the release of different sizes of growth hormone is altered with weight training.
  • The body can adapt and produce more or less of certain sizes of growth hormone with weight training. In this study, the larger sized growth hormone variants appear to increase with heavy resistance training.

“This study shows that not every form of growth hormone responds in the same way, but is dependent upon the exercise protocol,” Kraemer explained. “This may forever change the way we look at growth hormone in the circulation with exercise and training.”

Next stepThe researchers will next examine growth hormone and weight training in women who are using oral contraceptives.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Christine Guilfoy
American Physiological Society

Funding

This study was supported by a grant from the US Department of Defense Women’s Health Initiative.

The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has 10,500 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.

APS provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In 2004, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring.

We could not survive without hormones. They are among the most common and vital chemical messengers in the body. From head to toe, each moment of life, they signal cells to perform tasks that range from the ordinary to the extraordinary. Among their many roles, hormones help regulate body temperature, blood pressure, and blood sugar levels. In childhood, they help us “grow up.” In the teen years, they are the driving force behind puberty.

What Is A Hormone?

Hormones are powerful chemicals that help keep our bodies working normally. The term hormone is derived from the Greek word, hormo, which means to set in motion. And that’s precisely what hormones do in the body. They stimulate, regulate, and control the function of various tissues and organs. Made by specialized groups of cells within structures called glands, hormones are involved in almost every biological process including sexual reproduction, growth, metabolism, and immune function. These glands, including the pituitary, thyroid, adrenals, ovaries, and testes, release various hormones into the body as needed.

Levels of some hormones like parathyroid hormone, which helps regulate calcium levels in the blood and bone, actually increase as a normal part of aging and may be involved in bone loss leading to osteoporosis. But the levels of a number of other hormones, such as testosterone in men and estrogen in women, tend to decrease over time. In other cases, the body may fail to make enough of a hormone due to diseases and disorders that can develop at any age. When this occurs, hormone supplements—pills, shots, topical (rub-on) gels, and medicated skin patches—may be prescribed.

How Hormones Work

Most hormones exist in very low concentrations in the bloodstream. Each hormone molecule travels through the blood until it reaches a cell with a receptor that it matches. Then, the hormone molecule latches onto the receptor and sends a signal into the cell. These signals may instruct the cell to multiply, to make proteins or enzymes, or to perform other vital tasks. Some hormones can even stimulate a cell to release other hormones. However, no single hormone affects all cells in the same way. One hormone, for example, may stimulate a cell to perform one task, while the same hormone can have an entirely different influence over another cell. The response of some cells to hormonal stimulation also may change throughout life.

DHEA

Dehydroepiandrosterone or DHEA is made from cholesterol by the adrenal glands, which sit on top of each kidney. Production of this substance peaks in the mid-20s, and gradually declines with age in most people. What this drop means or how it affects the aging process, if at all, is unclear. In fact, scientists are somewhat mystified by DHEA and have not fully sorted out what it does in the body. However, researchers do know that the body converts DHEA into two hormones that are known to affect us in many ways: estrogen and testosterone.

Human Growth Hormone

Human growth hormone (hGH) is made by the pituitary gland, a pea-sized structure located at the base of the brain. It is important for normal development and maintenance of tissues and organs and is especially important for normal growth in children.

Studies have shown that injections of supplemental hGH are helpful to certain people. Sometimes children are unusually short because their bodies do not make enough  GH. When they receive injections of this hormone, their growth improves. Young adults who have no pituitary gland (because of surgery for a pituitary tumor, for example) cannot make the hormone and they become obese. When they are given hGH, they lose weight.

Like some other hormones, blood levels of hGH often decrease as people age.Although there is no conclusive evidence that hGH can prevent aging, some people spend a great deal of money on supplements. These supplements are claimed by some to increase muscle, decrease fat, and to boost an individual’s stamina and sense of well being. Shots—the only proven way of getting the body to make use of supplemental hGH—can cost more than $15,000 a year. They are available only by prescription and should be given by a doctor. Some dietary supplements, known as human growth hormone releasers, are marketed as a low-cost alternative to hGH shots. But claims that these over-the-counter products retard the aging process need to be examined. While some studies have shown that supplemental hGH does increase muscle mass, it seems to have less impact on muscle strength or function in older adults.

Testosterone

Ask an average man about testosterone, and he might tell you that this hormone helps transform a boy into a man. Or, he might tell that you that it has something to do with sex drive.   Or, if he has read news stories in recent years, he might mention male menopause, a condition thought to be caused by diminishing testosterone levels in aging men.

Testosterone is indeed a vital sex hormone that plays an important role in puberty. In men, testosterone not only regulates sex drive (libido), it also helps regulate bone mass, fat distribution, muscle mass and strength, and the production of red blood cells and sperm.But contrary to what some people believe, testosterone isn’t exclusively a male hormone.  

Women produce small amounts of it in their bodies as well. In men, testosterone is produced in the testes, the reproductive glands that also produce sperm. The amount of testosterone produced in the testes is regulated by the hypothalamus and the pituitary gland.

As men age, their testes often produce somewhat less testosterone than they did during adolescence and early adulthood, when productionof this hormone peaks. In fact, many of the changes that take place in older men often are incorrectly blamed on decreasing testosterone levels. Some men who have erectile difficulty (impotence), for instance, may be tempted to blame this problem on lowered testosterone. However, in many cases, erectile difficulties are due to circulatory problems, not low  testosterone. Still, some men may be helped by testosterone supplementation. For these few men who have extreme deficiencies, testosterone therapy in the form of patches, injections, or topical gels may offer substantial benefit.

Testosterone products may help a man with exceptionally low testosterone levels maintain strong muscles and bones, and increase sex drive. However, what effects testosterone replacement may have in healthy older men without these extreme deficiencies requires more research.The NIA is investigating the role of testosterone therapy in delaying or preventing frailty. Results from preliminary studies involving small groups of men have been inconclusive, and it remains unclear to what degree supplementation of this hormone can sharpen memory or help men maintain stout muscles, sturdy bones, and robust sexual activity.

Many other questions remain about the use of this hormone in late life. It is unclear, for example, whether men who are at the lower end of the normal range of testosterone production would benefit from supplementation.Some investigators are also concerned about the long-term harmful effects that supplemental testosterone might have on the aging body. While some epidemiologic studies suggest that higher levels of testosterone are not associated with the higher incidence of prostate cancer, it is not yet known if testosterone therapy increases the risk of such cancer, the second leading cause of cancer death among men.

The bottom line: Although some older men who have tried testosterone therapy report feeling more energetic or younger, testosterone supplementation remains a scientifically unproven method for preventing or relieving any physical and psychological changes that men with normal testosterone levels may experience as they get older. The NIA is expanding its research to gather more evidence on the risks and benefits of testosterone supplementation in aging men with low testosterone levels.

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Article adapted by MD Only Sports Weblog from original press release.
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Source:  National Institute on Aging