Testosterone makes a contribution to nitric oxide formation. Nitric oxide, released from penile nerves stimulates guanylate cyclase which catalyzes the transformation of guanosine-5-triphosphate into 3′,5′-cyclic, guanosine monophosphate (cyclic GMP). Gyclic GMP causes vasodilatation and hence erection formation (Morelli et al 2005). The breakdown of cyclic GMP to GMP is mediated by the enzyme, phosphodiesterase type-5, the inhibitors of which (eg, sildenafil citrate) enhance erection formation and maintanence (Carson and Lue 2005).
Trials of testosterone treatment in men with type 2 diabetes have also taken place. A recent randomized controlled crossover trial assessed the effects of intramuscular testosterone replacement to achieve levels within the physiological range, compared with placebo injections in 24 men with diabetes, hypogonadism and a mean age of 64 years (Kapoor et al 2006). Ten of these men were insulin treated. Testosterone treatment led to a significant reduction in glycated hemoglobin (HbA1C) and fasting glucose compared to placebo. Testosterone also produced a significant reduction in insulin resistance, measured by the homeostatic model assessment (HOMA), in the fourteen non-insulin treated patients. It is not possible to measure insulin resistance in patients treated with insulin but five out of ten of these patients had a reduction of insulin dose during the study. Other significant changes during testosterone treatment in this trial were reduced total cholesterol, waist circumference and waist-hip ratio. Similarly, a placebo-controlled but non-blinded trial in 24 men with visceral obesity, diabetes, hypogonadism and mean age 57 years found that three months of oral testosterone treatment led to significant reductions in HbA1C, fasting glucose, post-prandial glucose, weight, fat mass and waist-hip ratio (Boyanov et al 2003). In contrast, an uncontrolled study of 150 mg intramuscular testosterone given to 10 patients, average age 64 years, with diabetes and hypogonadism found no significant change in diabetes control, fasting glucose or insulin levels (Corrales et al 2004). Another uncontrolled study showed no beneficial effect of testosterone treatment on insulin resistance, measured by HOMA and ‘minimal model’ of area under acute insulin response curves, in 11 patients with type 2 diabetes aged between 33 and 73 years (Lee et al 2005). Body mass index was within the normal range in this population and there was no change in waist-hip ratio or weight during testosterone treatment. Baseline testosterone levels were in the low-normal range and patients received a relatively small dose of 100 mg intramuscular testosterone every three weeks. A good increase in testosterone levels during the trial is described but it is not stated at which time during the three week cycle the testosterone levels were tested, so the lack of response could reflect an insufficient overall testosterone dose in the trial period.
In fact, testosterone supplements might cause more problems than they solve. Studies have suggested a connection between supplements and heart problems. A 2010 study reported in The New England Journal of Medicine showed that some men over age 65 had an increase in heart problems when they used testosterone gel. A later of men younger than 65 at risk for heart problems and heart-healthy older men showed that both groups had a greater risk of heart attack when taking testosterone supplements.
Men on long-term testosterone appear to have a higher risk of cardiovascular problems, like heart attacks, strokes, and deaths from heart disease. For example, in 2010, researchers halted the Testosterone in Older Men study when early results showed that men on hormone treatments had noticeably more heart problems. "In older men, theoretical cardiac side effects become a little more immediate," Dr. Pallais says.
Dr. Anthony’s Notes: Vitamin D has about 100 other beneficial body functions outside of it's impact on testosterone. Make sure you take the active Vitamin D3 (not D2 – from plant sources!) It’s also advisable to get 20 minutes of sunshine daily (weather permitting) – without sunscreen. Verdict: this is one of the natural testosterone supplements that work. Best Food Sources of Vitamin D3: Wild Alaskan Salmon (#1), Sardines, Eggs How To Take Vitamin D3: Using 3000-5000IU of Vitamin D3 per day is a good safe, research supported dose. Your physician can also test your blood for D3 levels for more precise monitoring.
Some of these signs and symptoms can be caused by various underlying factors, including medication side effects, obstructive sleep apnea, thyroid problems, diabetes and depression. It's also possible that these conditions may be the cause of low testosterone levels, and treatment of these problems may cause testosterone levels to rise. A blood test is the only way to diagnose a low testosterone level.