The reason I started the experiment at that point is because I know a lot of guys who live my last-August lifestyle all the time, and I wanted to see what would happen to an “average” guy who turned things around. At the same time, there was no “normal” time in my life which would have been better for me to start the experiment. My stress level and diet fluctuates throughout the year anyway, so at any point, factors in my current lifestyle would have influenced the results. I wanted to begin at “ground zero.”


Another point I’d like to make for people worried about a link between high testosterone and prostate cancer is that it just doesn’t make sense. Prostate cancer becomes more prevalent in men as they age, and that’s also when their testosterone levels decline. We almost never see it in men in their peak testosterone years, in their 20s for instance. We know from autopsy studies that 8% of men in their 20s already have tiny prostate cancers, so if testosterone really made prostate cancer grow so rapidly — we used to talk about it like it was pouring gasoline on a fire — we should see some appreciable rate of prostate cancer in men in their 20s. We don’t. So, I’m no longer worried that giving testosterone to men will make their hidden cancer grow, because I’m convinced that it doesn’t happen.

At the National Population and Family Development Board in Malaysia, men between the ages of 31 and 52 were given two capsules of the herb (E. longifolia) in Andro400 every day for three weeks. They reported erections were stronger and, in some cases, lasted longer. Overall, they felt more virile. Their levels of testosterone doubled within three weeks.5
Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.[81] The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.[81] Thus it is the challenge of competition among males of the species that facilitates aggression and violence.[81] Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.[81] The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males.[81]
Hello everyone. First off, thank you Dr. Abraham Morgentaler, for the excellent and refreshing article. I do not intend to spill my guts about symptoms or values on here as it has already been done so many times over. I will say that I am an RN BSN and have been on HRT for going on 6 yrs. I live in Oklahoma and when I first started noticing symptoms I knew something was wrong and began to do research myself. With an initial level of 241 no doctor here at that time, would even consider HRT as I was only 35ish at the time.

In summary it’s important to know that this topic is still hotly debated, and there are a lot of inconsistencies in the data. We do know that soy contains phytoestrogens and does seem to have a lot of affects on the body, including some studies that show decreased Testosterone levels. For that reason (and the fact that it tastes like ass) I avoid it, and I recommend you also avoid it (in particular soy isolates!) if you’re seeking higher testosterone.
Costs were, in my opinion, very high especially for Axiron. I began reading all the health issues with drugs of this type. I became concerned and stopped using them. I took several over the counter supplements without much success. But recently I purchased from Briland Brands on amazon PaleoTest. I restarted a workout regimen and now feel great both during the workout and after. I can absolutely tell the difference. And it is a fraction of the price of the prescription drugs I took.
Testosterone is responsible for increased muscle mass. Leaner body mass helps control weight and increases energy. For men with low testosterone, studies that treatment can decrease fat mass and increase muscle size and strength. Some men reported a change in lean body mass but no increase in strength. It’s likely you’ll see the most benefits when you combine testosterone therapy with strength training and exercise.

Other stereotypical "macho" behaviors can affect testosterone in women, according to a 2015 report in the Proceedings of the National Academy of Sciences. For example, posing in a powerful way increases testosterone in both women and men. The 2015 report showed that having women role-play a position of power — acting like a boss — had the same effect.


Insulin causes lower Testosterone levels, so go easy on the carbs and eat more protein right? Well you need to be careful with protein consumption – Excess protein without fat can also cause insulin spikes. So go easy on that chicken breast with a side of egg white omelets washed down with a protein shake. From an insulin point of view you may as well drink a can of soda with some aminos acid! So what should you do? Eat more fat.
This evidence, together with the beneficial effects of testosterone replacement on central obesity and diabetes, raises the question whether testosterone treatment could be beneficial in preventing or treating atherosclerosis. No trial of sufficient size or duration has investigated the effect of testosterone replacement in primary or secondary prevention cardiovascular disease. The absence of such data leads us to examine the relationship of testosterone to other cardiovascular risk factors, such as adverse lipid parameters, blood pressure, endothelial dysfunction, coagulation factors, inflammatory markers and cytokines. This analysis can supply evidence of the likely effects of testosterone on overall cardiovascular risk. This has limitations, however, including the potential for diverging effects of testosterone on the various factors involved and the resultant impossibility of accurately predicting the relative impact of such changes.
To find the best testosterone booster, we collected every supplement available on BodyBuilding.com, and cross-checked our list against the top results on best of lists like MensFitness, BroScience, and BodyNutrition. We only looked at pills since some of the ingredients in testosterone boosters have a reputation for tasting bad, and powders just prolong the experience. There are a lot — 133 of them to be precise — and they all claim to boost testosterone levels. Testosterone (for men) is “thought to regulate sex drive (libido), bone mass, fat distribution, muscle mass and strength, and the production of red blood cells and sperm.” If a supplement can increase your natural testosterone levels, the rest should follow. As we mentioned above, it’s not that simple, and at best, you’ll experience only a short-lived boost.
In 2003, an Institute of Medicine panel concluded that there was insufficient evidence supporting the benefits of testosterone in older men and recommended further research. Consequently, in 2010, the National Institute of Aging, which is part of the NIH, launched the Testosterone Trials (T Trials) to figure out whether testosterone can help with symptoms associated with low levels of testosterone secondary to older age (i.e., symptomatic hypogonadism).
Consuming high amounts of sugary foods raises your blood glucose levels, which causes your body to release insulin as a response to the raised blood glucose levels. If not managed correctly, the body begins to develop a tolerance to insulin and cannot absorb the sugars in the blood stream as it used to, causing you to become insulin resistant. Being insulin resistant releases cortisol, and as you know, cortisol has extremely negative effects, lowering testosterone by quite a bit.
I am 56 and I have been taking 100 mg of Test Cyp IM once a week for the last 4 months. My total T fluctuates between 500 and 1000 and my E2 has been staying under 30 with the help of Arimidex 0.5 mg every 3.5 days. I do not know what my free T is due to the expense but I feel much better than I did. Not great but much better so I will continue. If you are not feeling good on TRT then you should have your E2 checked because it is probably over 30 which will counteract the effects of your free T.
In accordance with sperm competition theory, testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats.[40] This reaction engages penile reflexes (such as erection and ejaculation) that aid in sperm competition when more than one male is present in mating encounters, allowing for more production of successful sperm and a higher chance of reproduction.
My energy level have increased and my muscle mass has also increased, so I have positive results. As I said before I didn’t have a problem with achieving erections or maintaining, but with these injections I am now getting quite a good deal more spontaneous erections, and then when I do get one it does feels harder and stronger. The stronger and harder aspect is great, but the more often spontaneous is a bit annoying. 🙂

Glad to be heard. I have been using 10 times the recommended prescription dose of injectable test over the course of 6 years. Yes, 10 times the recommended dose. I use 250 at the lowest and 1000 mgs a week and sometimes 1200 mgs weekly. I am 50 years old. I look better than 90% of the 25 year olds I see in the gym. I have had zero issues. Acne a little , testicle shrinkage maybe 15%. No big deal. My sex drive is on fire. I bench pressed 340 pound today. I weigh 195 pounds and lean and muscles defined and hard as a rock. Doctors in the USA have no clue what they are doing. They read literature and have no experience or facts about test. They prescribe 50 mgs a week. Way short of what we as men need. Everyone is different, but 250mgs weekly is what we need typically. Injectable is the way to go. Gels are a weak joke. My doctor basically told me he was scared to prescribe more than 50 mgs weekly for fear of being sued if something went wrong. I found my own source and have been on top of the world for 6 years. Father died of prostate cancer. Mine prostate is fine. Prostate cancer from test is another example of ignorance in medical field. I am living proof that one can inject 10 times the recommended rate for the better part of a decade with no probs. I do hope the medical field catches up with the times and stops relying on archaic info.

Testosterone may decrease your chances of Alzheimer’s Disease. Several studies have linked low testosterone levels to an increased risk of Alzheimer’s disease.  In a 2010 study by the University of Hong Kong, researchers studied 153 Chinese men who were recruited from social centers. They were at least 55 years and older, lived in the community, and didn’t have dementia. Of those men, 47 had mild cognitive impairment — or problems with clear thinking and memory loss.


A: Testosterone production declines naturally with age. Low testosterone, or testosterone deficiency (TD), may result from disease or damage to the hypothalamus, pituitary gland, or testicles that inhibits hormone secretion and testosterone production. Treatment involves hormone replacement therapy. The method of delivery is determined by age and duration of deficiency. Oral testosterone, Testred (methyltestosterone), is associated with liver toxicity and liver tumors and so is prescribed sparingly. Transdermal delivery with a testosterone patch is becoming the most common method of treatment for testosterone deficiency in adults. A patch is worn, either on the scrotum or elsewhere on the body, and testosterone is released through the skin at controlled intervals. Patches are typically worn for 12 or 24 hours and can be worn during exercise, bathing, and strenuous activity. Two transdermal patches that are available are Androderm (nonscrotal) and Testoderm (scrotal). The Androderm patch is applied to the abdomen, lower back, thigh, or upper arm and should be applied at the same time every evening between 8 p.m. and midnight. If the patch falls off before noon, replace it with a fresh patch until it is time to reapply a new patch that evening. If the patch falls off after noon, do not replace it until you reapply a new patch that evening. The most common side effects associated with transdermal patch therapy include itching, discomfort, and irritation at the site of application. Some men may experience fluid retention, acne, and temporary abnormal breast development (gynecosmastia). AndroGel and Testim are transdermal gels that are applied once daily to the clean dry skin of the upper arms or abdomen. When used properly, these gels deliver testosterone for 24 hours. The gel must be allowed to dry on the skin before dressing and must be applied at least 6 hours before showering or swimming. Gels cannot be applied to the genitals. AndroGel is available in a metered-dose pump, which allows physicians to adjust the dosage of the medication. Side effects of transdermal gels include adverse reactions at the site of application, acne, headache, and hair loss (alopecia). For more specific information on treatments for low testosterone, consult with your doctor or pharmacist for guidance based on current health condition. Kimberly Hotz, PharmD
This being my initial use of product I do find an overall improvement in mind and body "maleness" related to focused goal and strength improvements. Has it turned me into a super stud..no, but at a recent 60th birthday, increased desire has added to performance and that is what I was looking for.I have reinstated diet and exercise that also has made physical and mental health achievements Will finish current bottle, and evaluate overall products worth once completed. Further evaluation pending...
To get your levels into the healthy range, sun exposure is the BEST way to optimize your vitamin D levels; exposing a large amount of your skin until it turns the lightest shade of pink, as near to solar noon as possible, is typically necessary to achieve adequate vitamin D production. If sun exposure is not an option, a safe tanning bed (with electronic ballasts rather than magnetic ballasts, to avoid unnecessary exposure to EMF fields) can be used.
FITNESS DISCLAIMER: The information contained in this site is for educational purposes only. Vigorous high-intensity exercise is not safe or suitable for everyone. You should consult a physician before beginning a new diet or exercise program and discontinue exercise immediately and consult your physician if you experience pain, dizziness, or discomfort. The results, if any, from the exercises may vary from person-to-person. Engaging in any exercise or fitness program involves the risk of injury. Mercola.com or our panel of fitness experts shall not be liable for any claims for injuries or damages resulting from or connected with the use of this site. Specific questions about your fitness condition cannot be answered without first establishing a trainer-client relationship.
In my late 40’s I was on Androgel. I lost weight and gained muscle; became healthier over all, brighter outlook, more active, and a harder erection that had a mind of it’s own. Then I went on injectable testosterone. My numbers are normal but my weight is up even after eating less. As well everything else is shelter smelter. I intend to get back to Androgel. (this, of course, is my own personal study)

Falling in love decreases men's testosterone levels while increasing women's testosterone levels. There has been speculation that these changes in testosterone result in the temporary reduction of differences in behavior between the sexes.[53] However, it is suggested that after the "honeymoon phase" ends—about four years into a relationship—this change in testosterone levels is no longer apparent.[53] Men who produce less testosterone are more likely to be in a relationship[54] or married,[55] and men who produce more testosterone are more likely to divorce;[55] however, causality cannot be determined in this correlation. Marriage or commitment could cause a decrease in testosterone levels.[56] Single men who have not had relationship experience have lower testosterone levels than single men with experience. It is suggested that these single men with prior experience are in a more competitive state than their non-experienced counterparts.[57] Married men who engage in bond-maintenance activities such as spending the day with their spouse/and or child have no different testosterone levels compared to times when they do not engage in such activities. Collectively, these results suggest that the presence of competitive activities rather than bond-maintenance activities are more relevant to changes in testosterone levels.[58]
2009 had heart attack, placed coronary stent, everything okay. Put on statins to keep lipid levels down to prevent further artery blockage. One year later developed Peyronie’s disease, low sex drive, fatigue, testicles withdrawn and hurting. Testosterone level was 85. Diagnosed with hypogonadism. Started Androgel, felt normal after a couple of weeks. I believe statins is the cause of my low T, you need lipids for hormone transport. Androgel could only bring my T level in the 250 range. Switched to Axiron (better, less messy), and my T level stays around 500 range. I get samples of Testim every now and then, it has a manly woody fragrance that women like. At present, I’m feeling a little fatigue, and mild dehydration. My lab work is always normal, except my red blood cells is always on the high side, almost abnormal. Next week I am going to donate some blood, to bring my RBC count down, and see if that will help.
It goes without saying that a healthy diet, quality sleep, productive lifestyle, and regular exercises can contribute to the overall increase of testosterone. However, it is also true that these activities are very often not enough for guys who have the problems with naturally low testosterone levels. This situation also includes people who want to boost their existing testosterone levels.
NHT works to reach a targeted level of hormones in your body, restoring your body’s natural ability to keep healthy and fit. Hormones are beneficial at any age, but most commonly we administer the therapy to people in their 40’s, when your body naturally begins to slow production of certain hormones. Supplementing these declining hormones can keep your body fit and active for much longer. Bio-identical hormones are made from plants and are identical to the hormones naturally produced by your own body. We never use synthetic hormones, which have been shown to increase your risk of heart disease and diabetes.
I need an answer regarding getting testoroene after having your Prostate removed. I had my Prostate removed 3 months ago and my PSA levels are zero. I want to go back on testoroene because I felt great when I was on it before having my prostate taken out. I am 44 years old and I workout 4-5 days a week hard. I am in excellent shape and I didn’t have any symptoms of prostate cancer other then my PSA levels went up.

It doesn’t get more natural than getting a good night’s sleep. Research published in the Journal of the American Medical Association showed that lack of sleep can greatly reduce a healthy young man’s testosterone levels. That effect is clear after only one week of reduced sleep. Testosterone levels were particularly low between 2 and 10 p.m. on sleep-restricted days. Study participants also reported a decreased sense of wellbeing as their blood testosterone levels dropped.
First, it’s important to note that these tactics and practices to boost testosterone naturally probably won’t work with men who have hypoandrogenism. If the glands and cells responsible for producing testosterone are damaged or defective, no amount of eggs or sleep will help you raise testosterone levels. You’ll likely need to use testosterone replacement therapy to get your T levels to a healthy place.
Tongkat ali (a.k.a. Longjack, a.k.a. Eurycoma Longifolia) is a foundational compound of Ayurveda, commonly used as an aphrodisiac. Similar to DHEA, longjack has been found to be effective in both men and women for improving libido, total and free testosterone concentrations as well as muscle mass and strength in men and women! And, unlike many of the other old world herbs commonly touted as natural testosterone boosters, longjack actually has a fair amount of human research denoting its benefits.
Xenoestrogen is a chemical that imitates estrogen in the human body. When men are exposed to too much of this estrogen-imitating chemical, T levels drop significantly. The problem is xenoestrogen is freaking everywhere — plastics, shampoos, gasoline, cows, toothpaste. You name it and chances are there are xenoestrogen in it. The ubiquitous nature of this chemical in our modern world is one reason some endocrinologists believe that testosterone levels are lower in men today than in decades past. It’s also a reason doctors say the number of boys born with hypospadias — a birth defect in which the opening of the urethra is on the underside of the penis and not at the tip — has doubled.  Note to expecting parents: make sure mom stays away from xenoestrogens during the pregnancy.
We scoured the database of the National Center for Biotechnology Information (part of the U.S. National Library of Science) for articles. Of the many ingredients marketed as boosting testosterone levels, we only found four backed by multiple articles based on human testing. For the best chance of boosting testosterone levels, a supplement needs to contain magnesium, fenugreek, and longjack — and some zinc wouldn’t go astray, either.
There are the testosterone deficiency signs, such as loss of sexual desire, erectile dysfunction, impaired fertility, chronic fatigue, etc. But it’s not always possible to understand which medical condition caused the decrease in testosterone levels. For example, if you always feel exhausted and have no sexual desire, it may provide evidence of depression.
I am generally dubious about supplement claims & have tried a few other Testosterone boosters which had no effect I could tell. Being desperate to find something to help me feel better, I ordered Dr Martin's T Booster. It arrived on May 14th and after the first day I felt better & noticeably had more energy. I don't have that tired dead feeling every morning now when trying to get out of bed. I am able to do some work & physical activities without being exhausted to the point of being sick. I have been taking Dr Martin's T-Booster for 8 days now. While I am not out running marathons yet, I am feeling much better & hope to continue getting better as I keep taking it

Infertility in men and women Infertility or a couple being unable to conceive a child can cause significant stress and unhappiness. There are numerous reasons for both male and female infertility but many ways in which medical assistance can overcome problems that people may face. Everything concerning infertility is discussed and explained here. Read now


• In a trial of men with anemia, 58% percent were no longer anemic after a year of therapy, compared to 22% who received a placebo. In addition, testosterone therapy was associated with higher hemoglobin levels. Hemoglobin is a protein in the blood that carries oxygen from the lungs to other areas of the body. It also brings carbon dioxide back to the lungs.

In non-human primates, it may be that testosterone in puberty stimulates sexual arousal, which allows the primate to increasingly seek out sexual experiences with females and thus creates a sexual preference for females.[39] Some research has also indicated that if testosterone is eliminated in an adult male human or other adult male primate's system, its sexual motivation decreases, but there is no corresponding decrease in ability to engage in sexual activity (mounting, ejaculating, etc.).[39]
Zinc is an essential mineral that plays an important role in improving testosterone levels as well as sperm production. Oysters are rich sources of this mineral. An increase in testosterone levels also helps improve your sexual desire and energy, which means that you are going to derive more pleasure from your sexual encounters besides having higher chances of conceiving.
2009 had heart attack, placed coronary stent, everything okay. Put on statins to keep lipid levels down to prevent further artery blockage. One year later developed Peyronie’s disease, low sex drive, fatigue, testicles withdrawn and hurting. Testosterone level was 85. Diagnosed with hypogonadism. Started Androgel, felt normal after a couple of weeks. I believe statins is the cause of my low T, you need lipids for hormone transport. Androgel could only bring my T level in the 250 range. Switched to Axiron (better, less messy), and my T level stays around 500 range. I get samples of Testim every now and then, it has a manly woody fragrance that women like. At present, I’m feeling a little fatigue, and mild dehydration. My lab work is always normal, except my red blood cells is always on the high side, almost abnormal. Next week I am going to donate some blood, to bring my RBC count down, and see if that will help.
Shilajit in its natural state has no chemical definition. In order to yield a consistent and efficacious form of shilajit, the shilajit is obtained from carefully selected rocks and is put through a patented technology where it is purified and standardized. This form of shilajit is now assured of optimal levels of bioactive components such as fulvic acid and dibenzo-pyrones, and is known as the patented PrimaVie.
For example, in February 2017, scientists reported on trials involving men over age 65 who had low testosterone due to aging. Each trial included a different number of men depending on the subject of the research. Roughly half of the participants received testosterone therapy for a year; the rest underwent a placebo treatment. The researchers discovered the following:
Smoking doesn’t promote maintaining male hormone levels healthy. The study has shown that smoking deprives the body from zinc. Zinc deficiency is dangerous for men because it is fraught with testosterone deficiency. The matter is that zinc is a kind of structural material for building the testosterone molecules. So, smoking combined with unhealthy diet strikes a blow against normal testosterone production.
Ginger is considered a safe herbal medicine with only few and insignificant adverse/side effects [1]. Some minor adverse effects such as mild diarrhea have been associated with the use of ginger in humans [19]. Ginger may also cause heartburn and at much higher doses act as a gastric irritant [19]. One study carried out on male diabetic rats concluded that extracts of Zingiber officinale have high safety and intake of Zingiber officinale roots as a drink may be useful for diabetic patients who suffer from sexual impotency [20].
That said, a group of researchers at the National University of Malaysia did a systemic literature review of longjack, looking for clinical research that demonstrated a relationship between the shrub and testosterone levels. Of 150 articles, only 11 met their inclusion criteria — involving humans and scientifically rigorous. However, of those 11 studies, seven “revealed remarkable association” between using longjack and improving male sexual health, while the remaining four “failed to demonstrate sufficient effects.” The team concluded that longjack looks “promising” when it comes to raising low testosterone, and that there is convincing evidence that it works.
It doesn’t get more natural than getting a good night’s sleep. Research published in the Journal of the American Medical Association showed that lack of sleep can greatly reduce a healthy young man’s testosterone levels. That effect is clear after only one week of reduced sleep. Testosterone levels were particularly low between 2 and 10 p.m. on sleep-restricted days. Study participants also reported a decreased sense of wellbeing as their blood testosterone levels dropped.
This common kitchen spice can actually play a role in testosterone production.  It has been said that through supplementing with ginger, that users have the ability to not only increase testosterone production naturally, but also improve sexual function and drive, improve sperm health, as well as increasing sperm count.  This is great for infertile men as well as those looking for another avenue when it comes to boosting natural testosterone levels.  

In the 2nd study, short-term testosterone treatment in older men significantly increased noncalcified coronary artery plaque volumes, possibly raising their risk of cardiovascular (CV) events,2 according to Matthew J. Budoff, MD, a professor of medicine at the David Geffen School of Medicine at UCLA and the Los Angeles Biomedical Research Institute in Torrance, California, and colleagues. 


With the ever-increasing interest in IGF-1, a growing number of legal, over-the-counter supplements have emerged which are aimed at amplifying the body’s own supply of this age-reversing hormone. The most common tend to be in the form of deer antler velvet extracts, delivered as a spray, due to the naturally occurring IGF-1 contained in the velvet itself.
“However, the parallels don’t necessarily follow logically, creating a real need to bring more evidence to this area so that physicians and patients would be able to make more  informed decisions based on the best possible evidence,” said Dr. Gill, a professor of medicine and the lead investigator at the Yale study site, the largest site participating in the TTrials, and coauthor of all 4 TTrials. 

The regular intake of testosterone boosters is known for the high level of safety comparing to the hormone injections and the use of illegal steroids. But still to protect yourself against any possible adverse reactions, you should remember that the supplementation can’t be continuous. The breaks from time to time are required. Such an approach to the use of boosters is healthy and best-working if you aspire to enhance own hormone production without any harm.


If you are serious about losing weight, you have got to strictly limit the amount of processed sugar in your diet, as evidence is mounting that excess sugar, and fructose in particular, is the primary driving factor in the obesity epidemic. So cutting soda from your diet is essential, as is limiting fructose found in processed foods, fruit juice, excessive fruit and so-called "healthy" sweeteners like agave.
Nutritional developers formulated Nugenix® with Testofen®, a key natural ingredient to help boost “free” testosterone along with resistance training. This key ingredient is carefully extracted from the fenugreek plant. A Testofen® study in Irvine, California indicated positive free testosterone-related results. Nugenix also includes L-Citrulline Malate, Tribulus, Zinc, plus Vitamins B6 and B12 to help promote overall health and performance.*
Before assessing the evidence of testosterone’s action in the aging male it is important to note certain methodological considerations which are common to the interpretation of any clinical trial of testosterone replacement. Many interventional trials of the effects of testosterone on human health and disease have been conducted. There is considerable heterogenicity in terms of study design and these differences have a potential to significantly affect the results seen in various studies. Gonadal status at baseline and the testosterone level produced by testosterone treatment in the study are of particular importance because the effects of altering testosterone from subphysiological to physiological levels may be different from those of altering physiological levels to supraphysiological. Another important factor is the length of treatment. Randomised controlled trials of testosterone have ranged from one to thirty-six months in duration (Isidori et al 2005) although some uncontrolled studies have lasted up to 42 months. Many effects of testosterone are thought to fully develop in the first few months of treatment but effects on bone, for example, have been shown to continue over two years or more (Snyder et al 2000; Wang, Cunningham et al 2004).
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