Below are brief descriptions of the papers referenced in this website. To see the abstract of a paper, click on the link where cited in the pertinent website pages
Abou-agag, 2005: Moderate alcohol increased vascular NO. Muscle relaxation was enhanced by moderate but reduced by more than moderate alcohol.
Agostini, 2011: In men who did not exercise, the incidence of some degree of reduced erectile function was increased 10-fold. Exercise is the single most important lifestyle factor that will improve erectile function, mainly through decreasing oxidative stress and preventing NO from being reduced by lack of antioxidant protection. Increasing age showed only a 20% increase whereas for inactivity the increase was over 1,000%! In other words, being physically active completely overwhelmed the relatively small impact of increasing age.
Akkus, 2002: In this study, moderate exercise decreased ED by two-thirds and severe exercise by 80%.
Aydioglu, 2008: In the mouse, alcohol reduced NO in the vascular lining but not neural NO. ED has not been reported to be increased with excessive alcohol. Perhaps that is because neural NO and therefore the increased blood flow from sexual arousal remains intact, while constriction of the penile arteries from stress may be blocked by the effects of alcohol on the central nervous system.
Bacon, 2003: Smoking, alcohol consumption and television viewing time as an indicator of inactivity were associated with ED.
Baumhakel, 2008: In patients with hypertension and metabolic syndrome, an angiotensin receptor blocker (ARB), irbesartan, improved erectile function, orgasmic function, and sexual satisfaction. Other hypertensive meds reduce erectile function. A man with hypertension and ED should make his desires clear for a choice of treatment that will be positive for his sex life.
BMI: The body mass index is a reasonable estimate of obesity, although more muscle tissue can elevate the index without indicating more fat. You can find your BMI by entering height and weight into the calculator on the link provided.
Brewis, 2005: It may be obvious to most but this study did document the decrease of intercourse with age. That is in part due to decreased erectile function, but it contributes to ED by less frequent and prolonged erections (Koskimaki, 2008).
Cayan, 2004: In this study after the treatment of male ED, the authors observed significant improvements in sexual arousal (p = 0.001), lubrication (p = 0.002), orgasm (p = 0.000), satisfaction (p = 0.000), and pain (p = 0.002) in the women. All were highly significant. While such effects may seem to be expected, it is difficult to overemphasize the effect of improved erectile function on a couple's relationship (sexual and in total).
Cheng, 2005: Using a sophysticated technique, the effect of sheer stress was shown on NO production in the artery lining. Sheer stress is the wrinkling of the artery lining resulting from faster blood flow as with exercise in the circulation as a whole or with the much larger increase in blood flow into the penis with sexual arousal.
Cheng, 2007: This meta-analysis showed a small decrease of ED with moderate alcohol intake.
Ciftci, 2007: This study of 40 men with ED compared the levels of PON-1 with those of 30 sexually active age-matched control men. Paraoxinase, a major circulating antioxidant, was highly significantly lower (119), compared to the controls (185), p=0.001. Antioxidants (within the body or ingested) protect NO during its formation and from being broken down.
David R Meldrum, 2012: In this review, we focused on metabolic aspects of ED. For example, diabetes, obsesity, smoking, and high fat and high sugar intake increase oxidative stress (OS), and exercise, antioxidants, and Viagra-like drugs can decrease OS. OS interfears with NO production and stability and therefore decreases blood flow to the penis. Excessive alcohol directly impairs NO in the vascular lining, but because neural NO release is not affected, it does not cause ED (decreased attention to stress may also preserve blood flow to the penis).
Dorey, 2004: In this landmark and exquisitely well-done study, pelvic floor exrecises were shown to significantly improve erectile function, and to a similar degree to the benefit of Viagra. The latter increases inflow of blood while the former decreases outflow of blood and increases erection hardness far above what can be achieved with inflow pressure alone. Any logical analysis would dictate that the maximum benefit will be achieved by combining efforts to maximize both increased inflow and decreased outflow (see Meldrum, 2014).
Dorey, 2005: This paper was based on the same study originally reported the year before. It is remarkable that 3/4 of the subjects had resolution or improvement of their ED without medication, yet 15 years later this fairly simple adjunct has enjoyed relatively little use. It's an old story that lifestyle changes are in general poorly promoted and utilized. With expensive pills it's an easy and quick measure to just write a prescription, and the large profits assure that the public is heavily exposed to promoting them (for example, statins rather than diet). However, in this case there are men with poor inflow that will not respond to PFE's and men with wide open penile veins that will not respond to efforts to increase inflow. The key is to do both.
Doumas, 2006: Men with hypertension (high blood pressure) were 2-3 times more likely to have ED and the ED was more severe. The ED increased with duration and severity of the HTN and with hypertensive medication. Men should have early treatment to prevent ED but also to lessen atherosclerosis, heart attacks and strokes. With HTN the arteries are constricted and blood flow to the tissues, including the penis, is decreased. Medications for HTN increase ED except with angiotensin II blockers (ARBs), which can improve erectile function at the same time as treating the HTN.
Esposito, 2002: In increase of inflammation caused by a sugar load was blocked with an antioxidant, confirming that the action of sugar in causing systemic inflammation is through oxidative stress.
Esposito, 2004: In this landmark study, 110 obese men with ED lost weight by reducing caloric intake and exercising. ED was strongly related to waist circumference. Weight loss improved ED and inflammation in the body compared with controls.
Esposito, 2006: In men with ED and metabolic syndrome the Mediterranean diet improved erectile function, lowered inflammation, insulin, triglycerides, LDL cholesterol, serum glucose, and blood pressure and increased vascular NO and HDL cholesterol. These remarkable effects indicate that dietary changes are likely to improve erectile function and health in many men.
Faridi, 2008: Sugar markedly decreases vascular NO due to oxidative stress. In this study a large sugar load (similar to a full sugar soda) only blocked about 2/3 of the increase of NO due to an amount of chocolate in a 40 gram portion of 55% cocoa. The study showed the high potency of chocolate and also confirmed, because an antioxidant blocked sugar's effect, that the harmfull effect of sugar on the vascular system is through oxidative stress. Practically, a desert with chocolate or berries is far better than taking the sugar load alone.
Feldman, 1994: The predictive value of ED for cardiovascular disease was high in young men (fifty-fold at ages 40-49) but dropped to just over 1% for men over age 70
Feldman, 2000: Smoking approximately doubled the risk of moderate to complete ED. Second hand smoke also increased ED. Smoking causes extreme oxidative stress. As with numerous other studies, smoke/smoking correlated with heart disease.
Ferrini, 2007: Long term continuous use of sildenafil (Viagra) helped to reduce age-related erectile dysfunction and penile fibrosis in a rat model. With age, both penile fibrosis, which prevents full distention of the penis with blood (and the secondary pressure on the penile veins) and decreased smooth muscle have been noted.
Ferrucci, 2006: "total n-3 fatty acids, were independently associated with lower levels of proinflammatory markers (IL-6, IL-1ra, TNFalpha, C-reactive protein) and higher levels of antiinflammatory markers (soluble IL-6r, IL-10, TGFbeta) independent of confounders; n-3 fatty acids may be beneficial in patients affected by diseases characterized by active inflammation."
Fisher, 2003: In healthy subjects, a flavinol-rich preparation of cocoa given for 4 days markedly increased NO (p = 0.009), with an additional dose causing a further rise 90 minutes after a dose (p = 0.01). Cocoa is the main ingredient of chocolate, which has been shown to be a strong antioxidant. The amount of sugar in a typical soda was only able to block about 2/3 of the NO rise induced a 40 gm amount of 55% cocoa chocolate (Katz, 2011). This study suggested that antioxidants may be of benefit for erectile performance in men without ED.
Gazzaruso, 2008: ED was a strong predictor of cardiac events and death in diabetics with angiographically proven but otherwise silent coronary artery disease. New onset of ED in a diabetic should indicate the need for assesment of the coronary arteries.
Goldberg, 2004: In this review you can find ways you can limit the buildup of these AGE's in your blood. They are implicated in aging and increase oxidative stress.
Halvorsen, 2006: This is a very helpful analysis of antioxidant potency in foods consumed in the U.S. The king is blackberries, which had twice as much per weight as blueberries (which are widely and inacurately considered to wear that crown). Note that cooking of vegetables and fruits (tomato is a fruit) increase antioxidant content. Spices are also strong antioxidants, but less is consumed.
Janszky, 2009: Consumption of chocolate twice or more per week was associated with a 2/3 reduction of dying after a first heart attack.
Katz, 2011: This is an excellent review of the health benefits of chocolate.
Koskimaki, 2008: Having intercourse less than once per week doubled the chance of having ED. That could be due to the ED, but the very large increase of blood flow into the penis greatly stimulated NO and would be expected to enhance erectile function. "Use it or lose it!"
Lavoisier, 1986: The pressure within the erection was measured. During voluntary contractions of the pelvic floor muscles the pressure increased by 100-525 mmHg. The normal blood pressure is 120, so these pressures were 2-4 times higher! Those higher pressures would markedly contribute to erectile quality and hardness.
Meldrum, 2010: This was our first review to emphasize that there are many lifestyle factors affecting erectile function and that the best results will be obtained when all are optimized.
Meldrum, 2011: In this review, in the American Journal of Cardiology, we highlighted erectile dysfunction as a critical warning sign of vascular disease. For example, cardiovascular disease is diagnosed an average of 39 months after the onset of ED. Blood tests and diseases that are often abnormal in cardiac patients (high cholesterol, low HDL cholesterol, elevated CRP, decreased nitric oxide (NO) in the lining of the arteries, an unhealthy diet, obesity, diabetes, high blood pressure) are also common in men with ED. Men with new onset of ED should be evaluated by their primary physician, with more extensive testing when the onset occurs before age 60.
Meldrum, 2012: This review focused on the metabolic changes underlying ED, proposed lifestyle changes, and treatments. Oxidative stress, insulin resistance and inflammation all play key roles in causing ED, and exercise, weight control, diet, and cessation of smoking are key interventions. Antioxidants, omega-3's, and the Viagra-like group of drugs are key treatments.
Meldrum, 2014: In this review we stressed that good erectile function depends on both maximizing inflow of blood and limiting outflow of blood. We therefore highlighted a study showing that pelvic floor exercises (PFE's), which help to constrict the penile veins, are as effective as the Viagra-like drugs (PDE-5 inhibitors) in treating ED. These two major ways to maximize erection hardness are not competitive, but add together because they apply to entirely different aspects of erectile hydraulics. As important is that there are men with poor inflow that will not respond to PFE's, and men with excessive outflow who will not respond to measures to increase inflow. The highest percentages of men will be helped by attacking both problems.
Meldrum, 2017: This review pointed out that lifestyle factors influencing semen quality/male infertility and ED are remarkably similar. Oxidative stress is a key factor in both, and omega-3's are helpful for both. A poor diet contributes to both. Exercise helps both. ED and male infertility are wake-up calls to improve lifestyle and health for many men. You can download a pdf (to the right of the screen when you click on the link).
Montorsi, 2002: In a study of men averaging 63 years of age, 2/3 had prior onset of ED. In those men it was an average 39 months before the diagnosis of diseased coronary artery/s.
O'leary, 2003: Aging is strongly correlated with ED (10% at age 40 rising to 80% for over 70). However, most of that increase is related to poor lifestyle factors such as increasing body weight, decreased frequency of coitus, decreased muscle mass, decreased exercise and pelvic floor strength, increased inflammation, and increased oxidative stress. All of those factors lead to cardiovascular disease and all can potentially be improved or prevented as discussed on the male aging page.
Okuda, 1997: Using the lining cells of human arteries (umbilical cord), an omega-3 raised NO production 3-fold.
Pace, 2010: Sildenafil (Viagra) was shown to help preserve erectile function following radical prostatectomy. That could be due to the helpful effects of penile exercise with its increased blood flow, but the Viagra-like drugs also may reduce oxidative stress. Preservation of erectile potency would also decrease the stress of worrying whether his love life might be over, which could help to make that true.
Pellufo, 2009: Smoking markedly decreases vascular NO. Those effects were completely reversed with 1,000 mg vitamin C and 800 IU vitamin E. It is therefore possible that emphasizing antioxidant intake and exercise may also reverse the ED and vascular disease in smokers. Clearly it is far better to quit, with smoking increasing multiple cancers and causing numerous other problems for themselves and others.
Rajfer, 1992: In this landmark study, Lou Ignarro studied penile tissue from human males and showed that NO was responsible for the neural stimulation of NO and that the action of NO was mediated by cyclic GMP. This showed that NO is a main stimulator of the erectile response caused by sexual arousal. Because the increase in blood flow was blocked by an inhibitor of cyclic GMP breakdown, their study led to the development of Viagra and other PDE-5 inhibitors. This study was part of the reason that Lou shared the 2008 Nobel Prize for the discovery of nitric oxide.
Salonia, 2012: Use of viagra-like drugs helps to preserve erectile function following radical prostatectomy by inducing spontaneous and intentional erectile activity. It may also help by decreasing both oxidative stress and psychological stress.
Segal, 2012: L-arginine, the raw material for NO production, is broken down by arginase. This study found that arginase increased with age. That could reduce erectile function. Men with low protein intake should take L-arginine tablets, 3,000 mg per day, which are widely available. Chicken and turkey are excellent sources in the diet.
Selvin, 2007: Diabetes and lack of physical activity were associated with ED. Using hours of TV watching as an excellent indicator of inactivity, lack of exercise was associated with a 2 to 3-fold increase of ED.
Senti, 2003: PON-1 is a principal circulating antioxidant. This study showed it was higher in active compared to inactive subjects. Of course the active group would have many individuals who did not exercise at optimal levels. Their findings fit with the stimulation of HDL cholesterol (beneficial for prevention of vascular disease) by physical activity. PON-1 is associated with HDL in the circulation and may explain part of its role in health.
Shafik, 2006: In this study, pressures within the erection greater than peak systolic pressure were shown to be reflex in nature. In another study, both distention of the penis and pressure on the tip (glans penis) caused these reflex contractions.
Sinclair Institute: This is an online service for couples to increase sexual arousal and enjoyment. They have instructional DVDs featuring various techniques (using couples in committed relationships) and sex toys available for purchase. As we pointed out, it is difficult to overemphasize the importance of sexual arousal in stimulating NO and inflow of blood into the penis, which is why this link is included.
Sousa, 2018: Walking was found to be associated with decreased strength of the pelvic floor muscles. There may be a tendency to relax those muscles during a relaxing walk. Walk briskly and contract those muscles. It's an easy way to do your pelvic floor exercises without taking any more time from your day.
Stanislavov, 2008: In this double-blinded, placebo contolled crossover study of men with mild to moderate ED, erectile quality markedly improved, intercourse frequency doubled, and serum cholesterol and blood pressure were reduced. The treatment was 80 mg of pycnogenol and 3 gm of L-arginine. Pycnogenol is a well-characterized mixture of polyphenolic antioxidants (like in berries, chocolate and red wine) shown to increase NO. The benefit of L-arginine alone is uncertain at this dose. However, men with low protein intake, such as vegetarians, should take 3 gm of L-arginine along with increasing antioxidants.
Stull, 2016: In this review, blueberries increased the body's sensitivity to insulin, and therefore glucose tolerance. Consumption of blueberries has also been linked to a decrease in type 2 diabetes, one of the most difficult and hazardous complications of obesity and aging.
Suh, 2004: Glutathione, a principal tissue antioxidant, decreases with age. This paper defined the mechanism and showed it was reversed by a strong antioxidant, lipoic acid. That means that ingesting strong antioxidants, like berries and pycnogenol (or lipoic acid), may decrease oxidative stress and support NO not only themselves, but also by preserving the body's own natural antioxidant protection. That is very much like the effect of exercise on Pon-1, a major circulating antioxidant.
Tagliabue, 2005:. The average levels of the active form of glutathione (1782) were highly significantly lower in men with ED compared to men without ED (2269), p < 0.001. GSH is a major natural antioxidant system in the body, providing protection for NO during synthesis and allowing it to last long enough to maximize lood flow into the penis. GSH was also lower in diabetics and moreso with diabetes and ED.
Tajkarimi, 2011: This paper gives a very detailed description of the pelvic floor muscles, which surround the lower penis. In young, presumably sexually active men the muscle attachment points to the penile sheath were significantly thicker, showing more muscle action. The younger men exercised those muscles during physical exercise and/or during intercourse, both of which decrease with age.
Tonetti, 2007: In this landmark study in the NEJM aggressive treatment of gingivitis (gum infection/inflammation previously linked to heart disease) decreased vascular NO and increased inflammatory markers compared to untreated controls. After 6 months the gingivitis was improved and NO increased to a level significantly above that of untreated controls. This paper shows both the vascular harm due to gingivitis, but also the benefit of treatment, which is what got it into such a prestigious journal.
Verit, 2010: With a dose of 20 mg of tadalafil (Cialis), total antioxidant status increased 45%, total serum oxidant status decreased 33% and serum PON-1 activity increased 50% (all p < 0.0001). The PDE-5 inhibitors improve erections by increasing cyclic-GMP, which has been shown to reduce oxidative stress.
Yang, 2006: Although done in rats, this study showed the importance of regular exercise. Acute exercise increased NO for 48 hours but daily exercise increased NO four-fold, lasting for a week.
Zuo, 2011: In this animal study, induced gingivitis increased inflammatory markers, decreased pressure in the erection, and decreased NO activity and cyclic GMP in penile tissue. These fundings clearly show that gingivitis can adversely affect erectile function.