Longitudinal studies in male aging studies have shown that serum testosterone levels decline with age (Harman et al 2001; Feldman et al 2002). Total testosterone levels fall at an average of 1.6% per year whilst free and bioavailable levels fall by 2%–3% per year. The reduction in free and bioavailable testosterone levels is larger because aging is also associated with increases in SHBG levels (Feldman et al 2002). Cross-sectional data supports these trends but has usually shown smaller reductions in testosterone levels with aging (Feldman et al 2002). This is likely to reflect strict entry criteria to cross-sectional studies so that young healthy men are compared to older healthy men. During the course of longitudinal studies some men may develop pathologies which accentuate decreases in testosterone levels.
There is a negative correlation of testosterone levels with plasminogen activator inhibitor-1 (PAI-1) (Glueck et al 1993; Phillips 1993), which is a major prothrombotic factor and known to be associated with progression of atherosclerosis, as well as other prothrombotic factors fibrinogen, α2-antiplasmin and factor VII (Bonithon-Kopp et al 1988; Glueck et al 1993; Phillips 1993; De Pergola et al 1997). There is a positive correlation with tissue plasminogen activator (tPA) which is one of the major fibrinolytic agents (Glueck et al 1993). Interventional trials have shown a neutral effect of physiological testosterone replacement on the major clotting factors (Smith et al 2005) but supraphysiological androgen administration can produce a temporary mild pro-coagulant effect (Anderson et al 1995).
Male hypogonadism becomes more common with increasing age and is currently an under-treated condition. The diagnosis of hypogonadism in the aging male requires a combination of symptoms and low serum testosterone levels. The currently available testosterone preparations can produce consistent physiological testosterone levels and provide for patient preference.
What you eat has a major impact on testosterone as well as other hormone levels. Therefore, you must pay attention to your long-term calorie intake and diet strategy. Constant dieting or overeating may disrupt your testosterone levels. Eating enough protein can help maintain healthy levels and aid in fat loss, which is also associated with your testosterone. Carb intake also plays a role, with research showing carbs can help optimize testosterone levels during resistance training.

You should also know that a lot of people are deficient in Vitamin D. In the USA & many other western regions in the world, vitamin D deficiency is at epidemic proportions. The best way to increase your D levels is sun exposure. You only need 20-30 minutes of exposure to a large amount of skin (i.e., take your shirt off and go for a walk during the day).
Experts have also found that fertile men have a lot of D-aspartic acid. D-aspartic acid is a complex amino acid linked with virility not found commonly. Oysters not only hold a good dose of D-aspartic acid but also has N-methyl-D-aspartate. N-methyl-D-aspartate sparks the production of sex hormones. Eating daily oysters has shown to be raising testosterone levels a lot in as little as six weeks.
Testosterone is an important enzyme that is most often associated with the process of puberty. However, both men and women have testosterone, and it is responsible for more than just transforming boys into men. Testosterone is also involved in maintaining bone density and regulating the levels of your red blood cells. Testosterone has also been shown to have a positive effect on muscle protein synthesis, essentially meaning that more testosterone can result in bigger muscles.
DHEA (dehydroepiandrosterone) extract - this is a chemical that used in your body which a ‘hormone precursor’. This means it’s the chemical used by the body to create hormones like oestrogen or testosterone. When taken as supplement it is believed to boost testosterone levels, but DHEA has not been shown to increase testosterone in men. DHEA comes in two form:
Zinc plays a variety of roles in regulating the functions of enzymes and chemicals as well as your immune system. Zinc is also a potent antioxidant and can reduce the frequency of illnesses. Studies show that zinc may actually increase testosterone production. Large doses of zinc have actually been found to inhibit aromatase, thus reducing estrogen levels and increasing the effects of testosterone.
The aim of treatment for hypogonadism is to normalize serum testosterone levels and abolish symptoms or pathological states that are due to low testosterone levels. The exact target testosterone level is a matter of debate, but current recommendations advocate levels in the mid-lower normal adult range (Nieschlag et al 2005). Truly physiological testosterone replacement would require replication of the diurnal rhythm of serum testosterone levels, but there is no current evidence that this is beneficial (Nieschlag et al 2005).

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Overall there is evidence that testosterone treatment increases lean body mass and reduces obesity, particularly visceral obesity, in a variety of populations including aging men. With regard to muscle changes, some studies demonstrate improvements in maximal strength but the results are inconsistent and it has not been demonstrated that these changes lead to clinically important improvements in mobility, endurance or quality of life. Studies are needed to clarify this. Changes in abdominal obesity are particularly important as visceral fat is now recognised as predisposing the metabolic syndrome, diabetes and cardiovascular disease.
"Some say it's just a part of aging, but that's a misconception," says Jason Hedges, MD, PhD, a urologist at Oregon Health and Science University in Portland. A gradual decline in testosterone can't explain a near-total lack of interest in sex, for example. And for Hedges' patients who are in their 20s, 30s, and early 40s and having erectile problems, other health problems may be a bigger issue than aging.