Garcinia cambogia sports research

Garcinia cambogia sports research
In addition to this, HCA helps lift depression and mood disorders, which can be very impactful for those who are emotional eaters.

Garcinia (hydroxycitric acid)

Scientific Name(s): Garcinia cambogia (Gaertn.) Desr. Family: Clusiaceae (Guttiferae)

Common Name(s): Malabar tamarind , hydroxycitric acid ( HCA )

The medical literature primarily documents weight loss and lipid-lowering activity for the plant. However, trials supporting its use are limited.

The dosages of G. cambogia extract in clinical trials ranged from 1,500 to 4,667 mg/day (25 to 78 mg/kg/day). The equivalent hydroxycitric acid (HCA) dose in the trials ranged from 900 to 2,800 mg/day (15 to 47 mg/kg/day). G. cambogia is available in capsule or tablet form with a maximum dose of 1,500 mg/day.

Contraindications

Avoid use if there is a known allergy or hypersensitivity to any components of G. cambogia .

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

The herb has documented drug interactions.

Adverse Reactions

At least 15 clinical studies involving approximately 900 patients document very mild adverse reactions. Most adverse reactions included headache, dizziness, dry mouth, and GI complaints such as nausea and diarrhea.

Toxicology

Toxicology studies resulted in no toxicity or deaths in animals at dosages of HCA 5,000 mg/kg, equivalent to 350 g or 233 times the maximum dosage of 1.5 g/day of HCA. In patients taking certain combination weight-loss supplements containing G. cambogia , severe or even fatal hepatotoxicity may occur.

The genus Garcinia is mainly distributed in tropical regions and includes approximately 200 species. G. cambogia belongs to the family Guttiferae and is found in India, Malaysia, and Africa. G. cambogia is commonly found in evergreen or semievergreen forests of southwest India, where 36 other species have been documented. 1 , 2 The plant species has variability in its branching pattern, fruit color, shape, and size. 1 The tree is small-to-medium in size with drooping branches. The leaves are dark green and glossy, oval-shaped with a narrow end, 5 to 12 cm in length, and 2 to 7 cm around. The tree is tolerant to drought and flowers during the hot season. The yellow, orange, or red fruit ripens during the rainy season and contains HCA. It is ovoid in shape, 5 centimeters around, has 6 to 8 seeds, and is listed in the US Department of Agriculture inventory of perennial edible fruits. 2

Dried fruit rinds have been used extensively for centuries throughout Southeast Asia for culinary purposes as a condiment and flavoring agent in place of tamarind or lemon. Additional culinary uses include the flavoring of curries, meat, and seafood. The fruit extract has been used as a flavoring agent for beverages and gourmet spices, as well as a carminative, thereby helping to prevent the formation of gas in the GI tract after a meal. HCA and other organic acids from the dried rind combined with salt help lower pH and provide a bacteriostatic effect used in curing fish. The herb is considered beneficial for overall health in the traditional Ayurvedic medical system. Rheumatism and bowel complaints are treated with a decoction of the fruit rind. A rinse is used from the herbal extract in veterinary medicine for some diseases of the mouth in cattle. HCA has also become popular as an ingredient for weight loss. 2 , 3 , 4

HCA is the primary medicinal component contained in the fruit rinds of G. cambogia . 5 HCA is present as up to 30% by weight in the pericarp of G. cambogia fruit. 6 Xanthones, xanthone derivatives, and polyisoprenylated benzophenones have been isolated. 6 , 7 Some salts used in commercial products are water soluble and bioavailable, and are a good source of calcium (495 mg) and potassium (720 mg). 8 Studies also document interest in production of HCA by using microorganisms. 9 , 10

Uses and Pharmacology

The medical literature primarily documents research on the weight loss and lipid-lowering activity of the plant.

In vitro and animal data

In 2 experiments using the human hepatoma cell line HepG2, overnight exposure to G. cambogia extract caused an upregulation of low-density lipoprotein (LDL) receptor activity and an upregulation of the level of HMG-CoA reductase resulting in decreased cholesterol synthesis. 11 Flavonoids from the plant reduced lipid levels in normal and hypercholesterolemic rats. 7 Reductions were also documented in triglycerides, phospholipids, and free fatty acids. The mechanism of action for the flavonoids may involve: (1) reducing the rate of lipogenesis by reducing the activities of lipogenic enzymes, glucose-6-phosphate dehydrogenase, and isocitrate dehydrogenase; and (2) increasing the rate of degradation of cholesterol leading to higher levels of hepatic and fecal bile acids, as well as neutral sterols in rats treated with the herb. While dexamethasone typically elevates lipid profiles, G. cambogia extract maintained normal lipid levels in rats administered dexamethasone. 12

In a 4-week randomized, double-blind, placebo-controlled trial, 150 obese patients were treated with a dietary supplement ( G. cambogia extract 55 mg, chitosan 240 mg, and chrome 19 mg) together with a weight reduction regimen. Treatment groups administered the dietary supplement showed statistically significant dose-related reductions in weight, total and LDL cholesterol, and triglycerides, and improvement in high density lipoprotein cholesterol. 13

The suggested mechanism of action involves HCA-inhibiting lipogenesis, increasing lipid oxidation, and reducing food intake. 3 , 14

A study in obese rats found high doses of HCA-containing G. cambogia (154 mmol HCA/kg diet) effective in suppressing epididymal adipose tissue. This same study also found testicular atrophy and toxicity at dosages of 778 mg HCA/kg body weight/day (102 mmol HCA/kg diet) and higher. 4 Another study in rats administered a high-fat diet and a mixture of G. cambogia extract, soypeptide, and L-carnitine, led to a reduction in body weight and accumulation of visceral fat mass. 15 The mixture also improved blood and hepatic lipid concentrations or the induced dyslipidemia in the rats.

This will at least insure that the manufacturer providing garcinia cambogia has certain standards, and provides high levels of HCA.

Other combination products with G. cambogia are also effective in reducing weight gain and improving dyslipidemia, hyperinsulinemia, hyperleptinemia, and fatty liver in mice. 16 The antiobesity effect involves modulation of several genes associated with visceral adipogenesis. One study in adult, nonobese cats found no effect on fat-free mass or energy expenditure. 17

In an 8-week randomized clinical trial, 40 patients were given either placebo or G. cambogia extract (500 mg/capsule) by mouth before each meal. Patients administered the extract exhibited weight loss and improvement in cholesterol and triglycerides when compared with the placebo group. 2

In a 12-week, randomized, double-blind, placebo-controlled study, 40 obese patients were treated with a combination supplement containing G. cambogia 50 mg as well as a 1,200 calorie diet per day. Two tablets of the supplement were taken by mouth 3 times a day after meals. The treatment group attained a 3.5 kg weight loss versus 1.2 kg on placebo, and a more than 85% reduction in fat loss in body composition measurements. The majority of the active group participants did not follow the diet regimen. 18

In a 12-week, double-blind, placebo-controlled, parallel group trial, 89 mildly overweight women were treated with a 1,200 kcal diet along with 2 caplets of G. cambogia 400 mg or matched placebo 3 times a day before each meal. At the end of the trial, both groups lost weight, but the treatment group achieved greater reduction in body weight. G. cambogia had no effect on appetitive variables. 14

Numerous studies document the safety profile of the calcium-potassium double salt of 60% HCA preparation (HCA-SX), as well as its bioavailability and efficacy in helping patients attain a healthy body weight. 3 , 19 , 20 , 21 , 22 , 23

An 8-week, randomized, placebo-controlled, double-blind study examined the efficacy of HCA-SX in 54 overweight patients. The treatment group was administered a combination supplement containing G. cambogia 500 mg 3 times a day while the control group received the placebo. All patients were asked to maintain a low-fat diet and drink 64 oz of water per day. The treatment group lost an average weight of 11.14 lb/person as compared with the control group, which lost an average of 4.2 lb/person. 19

Another 8-week, randomized, placebo-controlled, double-blind study examined the efficacy of HCA in 60 obese patients. The dosage regimen for HCA was 400 mg 3 times a day before each meal. All patients were on a low-fat diet and also instructed to exercise 3 times a week. Results indicated weight loss for the experimental group compared with the placebo group and that 87% of the weight loss in the HCA group was because of fat loss. Appetite scores were also reduced in the HCA-treated group. 19

Visceral, subcutaneous, and total fat accumulation were reduced in 39 patients over 16 weeks in a double-blind, randomized, placebo-controlled trial. The dosage regimen included HCA 1,000 mg/day versus placebo. At the end of the treatment, both groups were administered placebo for 4 weeks and no rebound effect was documented. 24

Another clinical study documented that treatment with HCA failed to produce weight change and fat mass change in patients. 25 However, the design of the clinical trial, the lack of bioavailability, and dosage of HCA used have been criticized. 2

Other pharmacologic activity

Some studies found that supplementation with G. cambogia can reduce oxidative damage. 26

The fruit contains xanthones, which inhibit pre-neoplastic lesions in mammary and colon cancer. The xanthones may also induce apoptosis in mouth, leukemia, breast, gastric, and lung cancer cell lines in vitro. 27

Glucose metabolism may be improved by lowering serum insulin levels in mice treated with G. cambogia . Leptin is a hormone associated with appetite control. G. cambogia may have leptin-like activity as mice treated with G. cambogia had decreased serum leptin levels and a reduced leptin/white adipose tissue ratio. 28 HCA treatment delayed and reduced intestinal glucose absorption in rats; the treatment causes delayed intestinal absorption of glucose rather than delayed gastric emptying. 29

HCA promoted lipid oxidation and reduced carbohydrate use in mice at rest and during running. 30 The utilization of respiratory gases was reduced for mice treated with HCA at rest and during exercise. Some studies on herbal coffee supplements with HCA showed an increase in resting energy expenditure to enhance metabolic rates and promote weight and fat loss. 31 , 32

Antiulcer activity was observed against induced gastric mucosal injury in rats with pretreatment of G. cambogia extract that decreased volume and acidity of gastric juice. 33 A similar study in rats found activity against indomethacin-induced gastric ulcers. 34 The anti-inflammatory activity of G. cambogia protected against induced colitis in rats. 35

Red blood cell count

A G. cambogia extract caused an increase in the red blood cell (RBC) count in rat tissue. The activity may be (1) associated with the iron in G. cambogia , as iron is an erythropoietic agent; (2) antioxidant activity and may decrease the rate of oxidant-induced hemolysis, which increases the life span of the RBC; or (3) the content of bioflavonoids in the plant, which may increase the level of peripheral testosterone, which can stimulate erythropoiesis in humans. 36

The dosages of G. cambogia extract in clinical trials ranged from 1,500 to 4,667 mg/day (25 to 78 mg/kg/day). The equivalent HCA dose in the trials ranged from 900 to 2,800 mg/day (15 to 47 mg/kg/day). 2 , 14 , 18 , 19 , 23 , 24 , 25 G. cambogia is available in capsule or tablet form with a maximum dose of 1,500 mg/day.

Pregnancy/Lactation

Due to lack of clinical and scientific information, use should be avoided during pregnancy and lactation.

And the best thing about getting fit, you not only achieve your goals of dropping the excess pounds but turn your life around too.

Although not a huge problem, most people would rather sit at their computer and have their questions answered live without being verbal over the phone.

One animal study in rats documented decreased maternal body weight gain during gestation. 37

Interactions

In patients taking medications for diabetes by mouth or insulin, G. cambogia may lower blood sugar levels. 28 , 29

G. cambogia contains iron and thus may have additive adverse reactions for patients taking medications for anemia. 36

Potassium and calcium supplements

Some commercial G. cambogia products contain adequate amounts of potassium and calcium. 8 Caution is advised for patients taking medications for heart disease, high blood pressure, or arrhythmia while supplementing with any product containing this herb.

A mouse study using a commercial polyherbal product containing G. cambogia found a potential serotonergic effect on food intake. Caution is advised for patients being treated for pain or taking medications for any psychiatric condition. 38

Singulair (or leukotriene receptor antagonists)

One case report documented fatal liver failure in a patient taking Singulair and 2 dietary supplements, one of which included G. cambogia and citrus derivatives. 39

A case report of rhabdomyolysisis is documented in a patient taking a combination herbal medicine containing G. cambogia . 40

In one case report, the international normalized ratio of a patient returned to normal after he stopped taking a combination herbal product containing G. cambogia . 41

Adverse Reactions

A total of 15 clinical studies involving approximately 900 patients documented very mild adverse reactions. Most adverse reactions included headache, dizziness, dry mouth, and GI complaints such as nausea and diarrhea. 2 , 42

Toxicology

Toxicology studies resulted in no toxicity or deaths in animals at HCA dosages of 5,000 mg/kg, equivalent to 350 g or 233 times the maximum dose of 1.5 g/day of HCA. 5 In patients taking certain combination weight-loss supplements containing G. cambogia , severe or even fatal hepatotoxicity may occur. 43 , 44 Some animal studies document testicular toxicity, 4 , 45 while other studies do not. 46 , 47

No unusual electrocardiographic effects (QTc interval or other electrocardiograph variables) were seen over 5 hours in patients taking half the recommended dose of a multicomponent weight loss supplement containing G. cambogia . 48 Patients receiving G. cambogia extract (1,667.3 mg/kg equivalent to 1,000 mg HCA/day) for 12 weeks exhibited no reproductive toxicity on serum testosterone, estrone, and estradiol levels. 49

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15. Kim YJ, Kim KY, Kim MS, Lee JH, Lee KP, Park T. A mixture of the aqueous extract of Garcinia cambogia , soy peptide and L: -carnitine reduces the accumulation of visceral fat mass in rats rendered obese by a high fat diet. Genes Nutr . 2008;2(4):353-358.

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17. Leray V, Dumon H, Martin L, et al. No effect of conjugated linoleic acid or Garcinia cambogia on fat-free mass, and energy expenditure in normal cats. J Nutr . 2006;136(suppl 7):1982S-1984S.

18. Thom E. A randomized, double-blind, placebo-controlled trial of a new weight-reducing agent of natural origin.

It’s best to check with your doctor first if you want to combine the two so your physician can provide the right dosage for your medications and ensure your safety.

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19. Lau FC, Bagchi M, Sen C, Roy S, Bagchi D. Nutrigenomic analysis of diet-gene interactions on functional supplements for weight management. Curr Genomics . 2008;9(4):239-251.

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21. Bagchi D, Deshmukh NS, Soni MG, Bagchi M. Safety of a novel calcium/potassium salt of (-)-hydroxycitric acid: I. Two generation reproduction toxicity study. Toxicol Lett . 2007;172(suppl 1):S190.

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26. Yonei Y, Takahashi Y, Hibino S, Watanabe M, Yoshioka T. Effects on the human body of a dietary supplement containing L-carnitine and Garcinia cambogia extract: a study using double-blind tests. J Clin Biochem Nutr . 2008;42(2):89-103.

27. Mazzio EA, Soliman KF. In vitro screening for the tumoricidal properties of international medicinal herbs. Phytother Res . 2009;23(3):385-398.

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29. Wielinga PY, Wachters-Hagedoorn RE, Bouter B, et al. Hydroxycitric acid delays intestinal glucose absorption in rats. Am J Physiol Gastrointest Liver Physiol . 2005;288(6):G1144-G1149.

30. Ishihara K, Oyaizu S, Onuki K, Lim K, Fushiki T. Chronic (-)-hydroxycitrate administration spares carbohydrate utilization and promotes lipid oxidation during exercise in mice. J Nutr . 2000;130(12):2990-2995.

31. Hoffman JR, Kang J, Ratamess NA, Jennings PF, Mangine G, Faigenbaum AD. Thermogenic effect from nutritionally enriched coffee consumption. J Int Soc Sports Nutr . 2006;3:35-41.

32. Taylor LW, Wilborn CD, Harvey T, Wismann J, Willoughby DS. Acute effects of ingesting Java Fittrade mark energy extreme functional coffee on resting energy expenditure and hemodynamic responses in male and female coffee drinkers. J Int Soc Sports Nutr . 2007;4:10.

33. Mahendran P, Sabitha KE, Devi CS. Prevention of HCl-ethanol induced gastric mucosal injury in rats by Garcinia cambogia extract and its possible mechanism of action. Indian J Exp Biol . 2002;40(1):58-62.

34. Mahendran P, Vanisree AJ, Shyamala Devi CS. The antiulcer activity of Garcinia cambogia extract against indomethacin-induced gastric ulcer in rats. Phytother Res . 2002;16(1):80-83.

35. dos Reis SB, de Oliveira CC, Acedo SC, et al. Attenuation of colitis injury in rats using Garcinia cambogia extract. Phytother Res . 2009;23(3):324-329.

36. Oluyemi KA, Omotuyi IO, Jimoh OR, Adesanya OA, Saalu CL, Josiah SJ. Erythropoietic and anti-obesity effects of Garcinia cambogia (bitter kola) in Wistar rats. Biotechnol Appl Biochem . 2007;46(pt 1):69-72.

37. Deshmukh NS, Bagchi M, Yasmin T, Bagchi D. Safety of a novel calcium/potassium salt of (-) hydroxycitric acid (HCA-SX): II. Developmental toxicity study in rats. Toxicol Mech Methods . 2008;18(5):443-451.

38. Kaur G, Kulkarni SK. Investigations on possible serotonergic involvement in effects of OB-200G (polyherbal preparation) on food intake in female mice. Eur J Nutr . 2001;40(3):127-133.

39. Actis GC, Bugianesi E, Ottobrelli A, Rizzetto M. Fatal liver failure following food supplements during chronic treatment with montelukast. Dig Liver Dis . 2007;39(10):953-955.

40. Mansi IA, Huang J. Rhabdomyolysis in response to weight-loss herbal medicine. [Published correction appears in: Am J Med Sci . 2004;328(2):129.] Am J Med Sci . 2004;327(6):356-357.

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45. Anno T, Oono H, Tamura K. Improvement of testicular toxicity in F/344DuCrj male rats fed Ca-type Garcinia cambogia extract by zinc supplemented diets. Nippon Shokuhin Kagaku Gakkaishi . 2005;12(3):121-127.

46. Shara M, Ohia SE, Yasmin T, et al. Dose- and time-dependent effects of a novel (-)-hydroxycitric acid extract on body weight, hepatic and testicular lipid peroxidation, DNA fragmentation and histopathological data over a period of 90 days. Mol Cell Biochem . 2003;254(1-2):339-346.

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Here are some of my favorite tips for losing weight using reliable methods that really work: Get good sleep!

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Copyright © 2009 Wolters Kluwer Health

Skipping Rope Doesn't Skip Workout

When was the last time you jumped rope? It's cheap and portable – and burns more calories than you might think. Give it a whirl!

WebMD archives content after 2 years to ensure our readers can easily find the most timely content.

">From the WebMD Archives

What piece of exercise equipment sells for under $20, fits into a briefcase, can be used by the whole family, and improves cardiovascular fitness while toning muscle at the same time? And using it for just 15-20 minutes will burn off the calories from a candy bar? The answer: a jump rope.

Jumping rope is a great calorie-burner. You'd have to run an eight-minute mile to work off more calories than you'd burn jumping rope. Use the WebMD Calorie Counter to figure out how many calories you'll burn for a given activity, based on your weight and the duration of exercise.

"It's certainly good for the heart," says Peter Schulman, MD, associate professor, Cardiology/Pulmonary Medicine, University of Connecticut Health Center in Farmington. "It strengthens the upper and lower body and burns a lot of calories in a short time, but other considerations will determine if it's appropriate for an individual."

He sees rope-jumping as something fit adults can use to add spice to their exercise routine. "You're putting direct stress on knees, ankles, and hips, but if done properly it's a lower-impact activity than jogging."

Basic Requirements

For novices, a beaded rope is recommended because it holds its shape and is easier to control than a lightweight cloth or vinyl rope.

  • Adjust the rope by holding the handles and stepping on the rope.
  • Shorten the rope so the handles reach your armpits.
  • Wear properly fitted athletic shoes, preferably cross-training shoes.

You'll need a four-by-six-foot area, and about 10 inches of space above your head. The exercise surface is very important. Do not attempt to jump on carpet, grass, concrete, or asphalt. While carpet reduces impact, the downside is it grabs your shoes and can twist your ankle or knee. Use a wood floor, piece of plywood, or an impact mat made for exercise.

How To Jump

If you haven't jumped rope since third grade, it can be humbling. It demands (and builds) coordination. Initially, you should practice foot and arm movements separately.

  • Hold both rope handles in one hand and swing the rope to develop a feel for the rhythm.
  • Next, without using the rope, practice jumping.
  • Finally, put the two together. You'll probably do well to jump continuously for one minute.

Alternate jumping with lower intensity exercise, such as marching, and you'll be able to jump for longer periods. You'll probably never want to jump for a solid 10 minutes. Rather, incorporate it into a varied exercise routine, such as one developed by Edward Jackowski, PhD, author of Hold It! You're Exercising Wrong. He uses rope-jumping intervals, initially 50-200 repetitions, in a combined aerobic and strengthening program.

The highest intensity workout involves one jump each time the rope passes. Slowing the rope to adding an extra little jump reduces the intensity. Pay attention to your target heart-rate zone. That's where you're exercising with enough intensity to benefit from the exercise and not so vigorously as to endanger your health.

Here's how to determine your maximal heart rate: 220 minus your age. The high end of your target zone is 85% of that number; the low end is 70% . If you're 40 years old, your maximal heart rate is 180, and your target zone is 126-153 beats per minute.

Preventing Injury

Check with your doctor if you have any doubts about your ability to withstand the impact and high aerobic intensity of rope-jumping. As mentioned, shoes and jumping surface are important. As with all exercise, warming up, stretching and cooling down are important. How you jump will determine the impact on your body.

"The real key is to make sure you jump properly," says Roger Crozier. He teaches physical education at Fox Run Elementary School in San Antonio, Texas, and coaches a competitive jump-rope team. "Stay high on the toes. When you walk or run, you impact your heel. With rope jumping you stay high on your toes and use your body's natural shock absorbers." Crozier says rope-jumping is lower impact than jogging or running if done properly. If not, it's considerably more impact.

"Beginners usually jump higher than necessary. With practice, you shouldn't come more than one inch off the floor.

Jump Rope for Heart

For nearly 25 years, Jump Rope for Heart has promoted fitness among elementary school students and raised money for heart research and education. It's sponsored by the American Heart Association, and Crozier is a volunteer who's developed training videos for participating schools. His students raised $11,000 in 2002.

"Jump Rope for Heart fits so well with physical education because we're fighting heart disease, the number one killer, and stroke, the number three killer," he says. "It's a chance to improve their own health while doing something good for someone else."

He teaches rope-jumping to kids in kindergarten through sixth grade.

[Effect of chromium yeast and chromium picolinate on body composition of obese, non-diabetic patients during and after a formula diet].

To say Crozier is enthusiastic about rope-jumping would be an understatement. "If you took all my P.E. equipment away except one thing, I can teach more with a jump rope than with any other piece of equipment."

He says besides being a great exercise in its own right, rope-jumping skills transfer to most athletic endeavors. "One of the key things as an educator I didn't realize until I started working with it is how it builds body awareness. With rope-jumping, you have to be aware of what your body is doing, and it's a great skill for connecting the brain's neurons."

While boxers come to mind as macho guys who jump rope, the U.S. Amateur Jump Rope Federation's national competition is televised. Yet there's still something of a gender issue. "The idea of it as a little girls' recess game is fading as the sport of jump rope grows," Crozier says. "Our competitive team is more heavily weighted with girls, but part of that is because boys have more options. In P.E. classes, it appeals to boys and girls equally."

Crozier says some parents become inspired to jump rope after watching their kids. "They're usually amazed at how hard it is," he says.

SOURCES: Roger Crozier, physical education teacher, Fox Run Elementary School, San Antonio, Texas, and training video advisor, American Heart Association "Jump Rope for Heart" • Peter Schulman, MD, associate professor, cardiology/pulmonary medicine, University of Connecticut Health Center, Farmington, Conn.

When to Treat a Sluggish Thyroid

By INGFEI CHEN

The symptoms are a laundry list of vague, common and easily overlooked complaints: tiredness, weight gain, ice-cold hands, thinning hair, constipation, depression and forgetfulness, to name a few. But for more than 10 million Americans, more often women than men, such woes are signs of something seriously wrong — a full-blown case of hypothyroidism, in which an underactive thyroid gland fails to crank out enough hormones.

By the Numbers

The deficiency is easily treated by replenishing the missing hormones with synthetic ones. The benefits can be stunning, almost instantly restoring some patients to their former selves and reversing the heart risks that can come with long-term unchecked hypothyroidism.

But despite the availability of a highly successful therapy for hypothyroidism, calibrating the correct drug dosage remains a challenge for patients and their doctors. And for certain patients with thyroids that are only slightly out of whack, determining whether treatment is warranted at all remains a subject of intense debate.

Roughly 20 percent of people on thyroid replacement therapy receive more hormone than they need. “It’s easy to inadvertently overtreat people with too much medication, which may have deleterious effects,” said Dr. David S. Cooper, director of the Johns Hopkins Thyroid Clinic in Baltimore.

Potential problems include irregular heart rhythms, especially for those over 60. Over-replacement may also weaken bones, with older patients and postmenopausal women at particular risk.

Undertreatment is also a worry — 20 percent of people on thyroid hormone don’t take enough medication. This can be particularly problematic in pregnant women, because an inadequate thyroid hormone supply raises the risk of miscarriage and premature birth and may harm brain development in the fetus. There is strong consensus that many pregnant women with hypothyroidism need an increase in their dose of thyroid medication. But that hazard has touched off a debate over whether every woman who is newly pregnant or contemplating pregnancy should be screened and treated for thyroid abnormalities.

Perhaps the most difficult issue in hypothyroidism is whether to treat one group of patients at all: those with a mildly lethargic thyroid, a condition known as subclinical hypothyroidism.

Some experts, and many patient advocates, urge that anyone with mild hypothyroidism be treated to relieve any symptoms and stave off overt thyroid failure and future cardiovascular trouble. Other clinicians think treatment is unwarranted, saying there is insufficient evidence that replacement therapy protects the heart in these patients, let alone makes them feel better.

Much of the controversy surrounds the question of what constitutes “normal” thyroid function.

The standard test for diagnosing hypothyroidism checks for blood levels of a hormone called thyroid-stimulating hormone, or T.S.H., that is secreted by the brain. Acceptable levels of the hormone, which does exactly what its name says, are considered to be roughly 0.5 to 4.1 milliunits per liter.

But some groups advocate lowering the upper limit of normal. The American Association of Clinical Endocrinologists, for instance, calls for dropping that value to 3.0 to identify otherwise undiagnosed cases — a controversial move that would more than double the count of all Americans considered to have abnormal thyroid function.

Complicating the picture is recent research suggesting that a normal T.S.H. level changes with age, and that the upper limit of normal may be much higher in the elderly.

Experts previously thought that subclinical hypothyroidism cropped up much more commonly in older people than in younger age groups, with roughly 15 percent of those 70 and above showing abnormal T.S.H. readings. A 2007 analysis, however, found that the upper limit of normal for an otherwise healthy person over 80 was 7.5, nearly double the current level.

The results imply that unless age-specific T.S.H. ranges are established, many people could be misclassified with hypothyroidism and receive unnecessary lifelong drug therapy.

Furthermore, it’s unclear whether treating subclinical hypothyroidism really helps head off heart trouble, particularly in the elderly.