HDL particles perform myriad functions, including immunomodulatory roles, the regulation of endothelial cell function and removal of cholesterol from the artery wall through reverse cholesterol transport . Importantly too, HDL-c concentrations in isolation may not be a reliable marker of CVD risk, since no long-term clinical data have established a link between the lower HDL-c concentrations caused specifically by TRT and increased incidence of CVD. In contrast, normalization of circulating T levels with transdermal TRT did not affect HDL-c levels in older, hypogonadal men . The HDL-c lowering effect appears variable with age, dose, and route of T administration and it is most striking with high-dose, oral therapy. Nonetheless, this HDL-c lowering effect has raised concern regarding the cardiovascular safety of TRT. The Annals of the New York Academy of Sciences has found that the use of anabolic steroids (which increases testosterone) among teenagers is correlated with increased likelihood of using violence. One study proposed that natural selection may have caused men to be more sensitive to situations in which their status is challenged, and that testosterone is the key factor that causes these situations to spark into aggression. The rise in testosterone during competition predicted aggression in males, but not in females. Studies have found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression. Testosterone and other androgens have evolved to motivate men to pursue competition, even when doing so leads to risk. Studies conducted have found direct correlation between testosterone and dominance, especially among the most violent criminals in prison who had the highest testosterone. A positive correlation exists between HDL-c and circulating T concentrations, as seen in multiple studies including the San Antonito Heart study , the Tromso study , the Turku Male Aging study , the Rancho Bernardo study , MRFIT and a study from Ghent, Belgium . The study endpoints include coronary artery plaque volume as measured by CT scan as well as serum lipids; thus, although resultant data merit interest, this study is underpowered to provide additional information regarding cardiovascular events. Overall, these types of retrospective analyses do not substantiate conclusions assigning a causal role for TRT in the development of cardiovascular morbidity but they clearly underscore the need for larger, randomized trials of TRT and CVD. In a second study, Finkle et al. used a large healthcare database and also reported an association between T prescriptions and myocardial infarction in older men in the immediate 90-day postprescription period . In contrast to the cross-sectional studies mentioned above, these studies have attempted to analyze large populations of men who received exogenous T, presumably as TRT. Nonetheless, the results of the TOM trial provide important cautionary information regarding the potential for TRT to be harmful in at least some populations of older men and points to the need for larger studies. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game. Higher testosterone levels in men reduce the risk of becoming or staying unemployed. Serious side effects may include liver toxicity, heart disease (though a randomized trial found no evidence of major adverse cardiac events compared to placebo in men with low testosterone), and behavioral changes. Preliminary evidence suggests that low testosterone levels may be a risk factor for cognitive decline and possibly for dementia of the Alzheimer's type, a key argument in life extension medicine for the use of testosterone in anti-aging therapies. Exercise is another powerful lifestyle factor that works with testosterone therapy. When men start testosterone therapy, they often want to feel stronger, have more energy, or improve their quality of life. For men who already have heart disease, the relationship between TRT and cholesterol becomes more sensitive. Diabetes and metabolic syndrome (a condition involving high blood pressure, high blood sugar, and abnormal cholesterol) often go hand in hand with low testosterone. Fat tissue, especially around the belly, lowers natural testosterone levels. Older men are more likely to already have heart disease, diabetes, or high blood pressure. A combination of healthy fats, regular exercise, proper diet, weight management, and lifestyle modifications can help counteract any potential reductions in HDL. A combination of a balanced diet and regular exercise can help achieve and sustain a healthy weight. Maintaining a healthy weight is crucial for optimal lipid balance. The degree of change often depends on factors such as dosage, duration of therapy, lifestyle habits, and individual metabolic responses. Managing SHBG is difficult, as there body typically tries to make more or less depending on many factors. The primary way to treat triglycerides is through diet. The Organon group in the Netherlands were the first to isolate the hormone, identified in a May 1935 paper "On Crystalline Male Hormone from Testicles (Testosterone)". Suffering the ridicule of his colleagues, he abandoned his work on the mechanisms and effects of androgens in human beings. He reported in The Lancet that his vigor and feeling of well-being were markedly restored but the effects were transient, and Brown-Séquard's hopes for the compound were dashed. Testosterone has been detected at variably higher and lower levels among men of various nations and from various backgrounds, explanations for the causes of this have been relatively diverse. Testosterone's bioavailable concentration is commonly determined using the Vermeulen calculation or more precisely using the modified Vermeulen method, which considers the dimeric form of sex hormone-binding globulin. Two of the immediate metabolites of testosterone, 5α-DHT and estradiol, are biologically important and can be formed both in the liver and in extrahepatic tissues. Certain cytochrome P450 enzymes such as CYP2C9 and CYP2C19 can also oxidize testosterone at the C17 position to form androstenedione.
