Nosso atleta e Médico Eduardo Zaeyen, separou um artigo bem interessante sobre Hormonios do Crescimento. Aproveite a leitura...
fonte:www.health.harvard.edu/newsletters/Harvard_Mens_Health_Watch/2010/May/growth-hormone-athletic-performance-and-aging
MAY 2010
In 1513, the Spanish explorer Juan Ponce de León
arrived in Florida to search for the fountain of youth. If he got any benefit
from his quest, it was due to the exercise involved in the search.
Few men today believe in miraculous waters, but
many, it seems, believe in the syringe of youth. Instead of drinking
rejuvenating waters, they inject human growth hormone to slow the tick of the
clock. Some are motivated by the claims of the "anti-aging" movement,
others by the examples of young athletes seeking a competitive edge. Like Ponce
de León, the athletes still get the benefit of exercise, while older men may
use growth hormone shots as a substitute for working out. But will growth
hormone boost performance or slow aging? And is it safe?
Human growth hormone: Up
close and personal
Growth hormone (GH) is a small protein that is made
by the pituitary gland and secreted into the bloodstream. GH production is
controlled by a complex set of hormones produced in the hypothalamus of the
brain and in the intestinal tract and pancreas.
The pituitary puts out GH in bursts; levels rise
following exercise, trauma, and sleep. Under normal conditions, more GH is
produced at night than during the day. This physiology is complex, but at a
minimum, it tells us that sporadic blood tests to measure GH levels are
meaningless since high and low levels alternate throughout the day. But
scientists who carefully measure overall GH production report that it rises
during childhood, peaks during puberty, and declines from middle age onward.
GH acts on many tissues throughout the body. In
children and adolescents, it stimulates the growth of bone and cartilage. In
people of all ages, GH boosts protein production, promotes the utilization of
fat, interferes with the action of insulin, and raises blood sugar levels. GH
also raises levels of insulin-like growth factor-1 (IGF-1).
Therapeutic use
GH is available as a prescription drug that is
administered by injection. GH is indicated for children with GH deficiency and
others with very short stature. It is also approved to treat adult GH
deficiency — an uncommon condition that almost always develops in conjunction
with major problems afflicting the hypothalamus, pituitary gland, or both. The
diagnosis of adult GH deficiency depends on special tests that stimulate GH
production; simple blood tests are useless at best, misleading at worst.
Adults with bona fide GH deficiencies benefit from
GH injections. They enjoy protection from fractures, increased muscle mass,
improved exercise capacity and energy, and a reduced risk of future heart
disease. But there is a price to pay. Up to 30% of patients experience side
effects that include fluid retention, joint and muscle pain, carpal tunnel
syndrome (pressure on the nerve in the wrist causing hand pain and numbness),
and high blood sugar levels.
GH doping
Adults who are GH deficient get larger muscles,
more energy, and improved exercise capacity from replacement therapy. Athletes
work hard to build their muscles and enhance performance. Some also turn to GH.
It's not an isolated problem. Despite being banned
by the International Olympic Committee, Major League Baseball, the National
Football League, and the World Anti-Doping Agency, GH abuse has tainted many
sports, including baseball, cycling, and track and field. Competitive athletes
who abuse GH risk disqualification and disgrace. What do they gain in return?
And do they also risk their health?
Because GH use is banned and athletic performance
depends on so many physical, psychological, and competitive factors, scientists
have been unable to evaluate GH on the field. But they can conduct randomized
clinical trials that administer GH or a placebo to healthy young athletes and
then measure body composition, strength, and exercise capacity in the lab.
A team of researchers from California conducted a
detailed review of 44 high-quality studies of growth hormone in athletes. The
subjects were young (average age 27), lean (average body mass index 24), and
physically fit; 85% were male. A total of 303 volunteers received GH
injections, while 137 received placebo.
After receiving daily injections for an average of
20 days, the subjects who received GH increased their lean body mass (which
reflects muscle mass but can also include fluid mass) by an average of 4.6
pounds. That's a big gain — but it did not translate into improved performance.
In fact, GH did not produce measurable increases in either strength or exercise
capacity. And the subjects who got GH were more likely to retain fluid and
experience fatigue than were the volunteers who got the placebo.
If you were a jock in high school or college,
you're likely to wince at the memory of your coach barking "no pain, no
gain" to spur you on. Today, athletes who use illegal
performance-enhancing drugs risk the pain of disqualification without proof of
gain.
GH for aging
Among its many biological effects, GH promotes an
increase in muscle mass and a decrease in body fat. As men age, GH levels fall.
During the same time span, muscle mass declines and body fat increases. And so,
the theory goes, the way to arrest these effects of aging is to inject GH.
Similar claims have been made for other hormones
that decline with age, including testosterone and dehydroepiandrosterone (DHEA)
in men, and estrogen in women. Research shows that estrogen replacement does
more harm than good in older women, and there is no solid evidence that
testosterone and DHEA are safe and effective for healthy older men. But that
has not stopped the growth of "anti-aging" and "regenerative
medicine" clinics and Web sites.
Expensive injections of growth hormone are offered
by many practitioners, even though the FDA has not approved the use of GH for
anti-aging, body building, or athletic enhancement, and the marketing or
distribution of the hormone for any of these purposes is illegal in the U.S.
According to one estimate, 20,000 to 30,000 Americans used GH as
"anti-aging" therapy in 2004 alone; according to another, 100,000
people received GH without a valid prescription in 2002.
To evaluate the safety and efficacy of GH in
healthy older people, a team of researchers reviewed 31 high-quality studies
that were completed after 1989. Each of the studies was small, but together
they evaluated 220 subjects who received GH and 227 control subjects who did
not get the hormone. Two-thirds of the subjects were men; their average age was
69, and the typical volunteer was overweight but not obese.
The dosage of GH varied considerably, and the
duration of therapy ranged from two to 52 weeks. Still, the varying doses succeeded
in boosting levels of IGF-1, which reflects the level of GH, by 88%.
As compared to the subjects who did not get GH, the
treated individuals gained an average of 4.6 pounds of lean body mass, and they
shed a similar amount of body fat. There was a slight drop in total cholesterol
levels, but no significant changes in LDL ("bad") cholesterol, HDL
("good") cholesterol, triglycerides, aerobic capacity, bone density,
or fasting blood sugar and insulin levels. But GH recipients experienced a high
rate of side effects, including fluid retention, joint pain, breast
enlargement, and carpal tunnel syndrome. The studies were too short to detect
any change in the risk of cancer, but other research suggests an increased risk
of cancer in general and prostate cancer in particular.
Beat the clock
"Every man desires to live long," wrote
Jonathan Swift, "but no man would be old." He was right, but the
fountain of youth has proved illusory. And while more study is needed, GH does
not appear to be either safe or effective for young athletes or healthy older
men. But that doesn't mean you have to sit back and let Father Time peck away
at you. Instead, use the time-tested combination of diet and exercise. Aim for
a moderate protein intake of about .36 grams per pound of body weight; even big
men don't need more than 65 grams (about 2¼ ounces) a day, though athletes and
men recovering from illnesses or surgery might do well with about 20% more.
Plan a balanced exercise regimen; aim for at least 30 minutes of moderate exercise,
such as walking, a day, and be sure to add strength training two to three times
a week to build muscle mass and strength. You'll reduce your risk of many
chronic illnesses, enhance your vigor and enjoyment of life, and — it's true —
slow the tick of the clock.
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