The oldest form is an injection, which we still use because it’s inexpensive and because we reliably get good testosterone levels in nearly everybody. The disadvantage is that a man needs to come in every few weeks to get a shot. A roller-coaster effect can also occur as blood testosterone levels peak and then return to baseline. [See “Exogenous vs. endogenous testosterone,” above.]
When females have a higher baseline level of testosterone, they have higher increases in sexual arousal levels but smaller increases in testosterone, indicating a ceiling effect on testosterone levels in females. Sexual thoughts also change the level of testosterone but not level of cortisol in the female body, and hormonal contraceptives may affect the variation in testosterone response to sexual thoughts.
Hypogonadism is highly prevalent amongst men with diabetes mellitus type 2 or symptoms of the metabolic syndrome, including insulin resistance, impaired glucose regulation, obesity, and hypertension.1,6,13,14,17,18 Low testosterone in many men with diabetes remains undiagnosed and untreated, and current guidelines recommend measurement of testosterone levels in such patients and, equally, that such chronic diseases should be investigated and treated in men with hypogonadism.1,6 It is not yet fully known whether diabetes is a cause or a consequence of low testosterone, and the full effects of testosterone administration on glycemic control in hypogonadal men with diabetes are unclear. However, there are indications that treating hypogonadism may have benefits on metabolic status in men with diabetes, and there is evidence that testosterone replacement therapy has a beneficial effect on risk factors for diabetes such as central obesity, insulin sensitivity, glucose control and blood lipid profiles in hypogonadal men with type 2 diabetes.14,19,20
Another study in 2015 by Melville and friends gave subjects either three or six grams of DAA per day for a 14 days (2 weeks). Researchers noted that the 3g dose of D-aspartic acid did not result in any meaningful changes in testosterone levels (or any other anabolic hormones for that matter). However, the group of men receiving 6g per day experienced a significant reduction in both total testosterone and free testosterone levels, with no concurrent change in other hormones tested.
Around age 30, men’s testosterone levels begin a long, gradual decline. (According to the FDA, normal T range is between 300 to 1,000 nanograms per deciliter (ng/dl) of blood serum. Anything below 300 ng/dl is considered low.) If a blood test confirms you have low T, your doctor may recommend a prescription testosterone supplement or replacement therapy.
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.