Michael T. Murray, ND, is widely regarded as one of the leading authorities on natural medicine. He is the author of many books, including the classic Encyclopedia of Nutritional Supplements. His latest book is What the Drug Companies Won’t Tell You and Your Doctor Doesn’t Know. Visit him online at doctormurray.com.   Article Courtesy of Better Nutrition  
Any day that you don’t get 20 minutes of direct sunlight on your skin, you want to supplement with 5,000 IUs of vitamin D3. If you get your blood levels tested and you’re extremely low — below 50 IUs — you typically want to do 5,000 IUs twice a day for three months until you get those numbers up. You can do everything in the world, but if your vitamin D levels aren’t right, your testosterone levels will stay low.
A team led by Dr. Joel Finkelstein at Massachusetts General Hospital investigated testosterone and estradiol levels in 400 healthy men, 20 to 50 years of age. To control hormone levels, the researchers first gave the participants injections of a drug that suppressed their normal testosterone and estradiol production. The men were randomly assigned to 5 groups that received different amounts (from 0 to 10 grams) of a topical 1% testosterone gel daily for 16 weeks. Half of the participants were also given a drug to block testosterone from being converted to estradiol.

Testosterone is observed in most vertebrates. Testosterone and the classical nuclear androgen receptor first appeared in gnathostomes (jawed vertebrates).[189] Agnathans (jawless vertebrates) such as lampreys do not produce testosterone but instead use androstenedione as a male sex hormone.[190] Fish make a slightly different form called 11-ketotestosterone.[191] Its counterpart in insects is ecdysone.[192] The presence of these ubiquitous steroids in a wide range of animals suggest that sex hormones have an ancient evolutionary history.[193]
Afrisham, R., Sadejh-Nejadi, S., SoliemaniFar, O., Kooti, W., Ashtary-Larky, D., Alamiri, F., … Khaneh-Keshi, A. (2016, November 24). Salivary testosterone levels under psychological stress and its relationship with rumination and five personality traits in medical students. Psychiatry Investigations, 13(6), 637–643. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5128352/
The effects of testosterone in humans and other vertebrates occur by way of multiple mechanisms: by activation of the androgen receptor (directly or as DHT), and by conversion to estradiol and activation of certain estrogen receptors.[109][110] Androgens such as testosterone have also been found to bind to and activate membrane androgen receptors.[111][112][113]
When testosterone and endorphins in ejaculated semen meet the cervical wall after sexual intercourse, females receive a spike in testosterone, endorphin, and oxytocin levels, and males after orgasm during copulation experience an increase in endorphins and a marked increase in oxytocin levels. This adds to the hospitable physiological environment in the female internal reproductive tract for conceiving, and later for nurturing the conceptus in the pre-embryonic stages, and stimulates feelings of love, desire, and paternal care in the male (this is the only time male oxytocin levels rival a female's).[citation needed]
It may be unlikely to completely eliminate products with EDCs, but there are a number of practical strategies that you can try to limit your exposure to these gender-bending substances. The first step would be to stop using Teflon cookware, as EDCs can leach out from contaminated cookware. Replace them with ceramic ones. Stop eating out of cans, as the sealant used for the can liner is almost always made from powerful endocrine-disrupting petrochemicals known as bisphenols, e.g. Bisphenol A,
Testosterone may prove to be an effective treatment in female sexual arousal disorders,[52] and is available as a dermal patch. There is no FDA approved androgen preparation for the treatment of androgen insufficiency; however, it has been used off-label to treat low libido and sexual dysfunction in older women. Testosterone may be a treatment for postmenopausal women as long as they are effectively estrogenized.[52]
Cross-sectional studies have found a positive association between serum testosterone and some measures of cognitive ability in men (Barrett-Connor, Goodman-Gruen et al 1999; Yaffe et al 2002). Longitudinal studies have found that free testosterone levels correlate positively with future cognitive abilities and reduced rate of cognitive decline (Moffat et al 2002) and that, compared with controls, testosterone levels are reduced in men with Alzheimer’s disease at least 10 years prior to diagnosis (Moffat et al 2004). Studies of the effects of induced androgen deficiency in patients with prostate cancer have shown that profoundly lowering testosterone leads to worsening cognitive functions (Almeida et al 2004; Salminen et al 2004) and increased levels of serum amyloid (Gandy et al 2001; Almeida et al 2004), which is central to the pathogenesis of Alzheimer’s disease (Parihar and Hemnani 2004). Furthermore, testosterone reduces amyloid-induced hippocampal neurotoxity in vitro (Pike 2001) as well as exhibiting other neuroprotective effects (Pouliot et al 1996). The epidemiological and experimental data propose a potential role of testosterone in protecting cognitive function and preventing Alzheimer’s disease.
Ashwagandha is shown to be effective at reducing cortisol which in turn helps with testosterone production. There are also numerous studies showing the effects on improving testosterone in infertile men (ref 80).  If you are using the Aggressive Strength product you don't need to supplement with ashwagandha as it's included in the test booster formula. Likewise if you're using Tian Chi (my daily herb drink).
Sprinting has been shown numerous times that it has positive effects on testosterone levels. One 2011 study (ref 84) looked at weightlifters who performed 4x35m sprints twice a week. In contrast to the control group (who continued lifting but did not sprint), it was found that “After the 4-week training program, total testosterone and the total testosterone/cortisol ratio increased significantly in the (sprinters) EXP group”.

A recent study compared total and bioavailable testosterone levels with inflammatory cytokines in men aged 65 and over. There was an inverse correlation with the pro-inflammatory soluble interleukin-6 receptor, but no association with interleukin-6 (IL-6), highly sensitive CRP (hsCRP), tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β (Maggio et al 2006). Another trial found that young men with idiopathic hypogonadotrophic hypogonadism had higher levels of proinflammatory factors interleukin-2 (IL-2), interleukin-4 (IL-4), complement C3c and total immunoglobulin in comparison to controls (Yesilova et al 2000). Testosterone treatment in a group of hypogonadal men, mostly with known coronary artery disease, induced anti-inflammatory changes in the cytokine profile of reduced IL-1β and TNF-α and increased IL-10 (Malkin, Pugh, Jones et al 2004).

Falling in love decreases men's testosterone levels while increasing women's testosterone levels. There has been speculation that these changes in testosterone result in the temporary reduction of differences in behavior between the sexes.[53] However, it is suggested that after the "honeymoon phase" ends—about four years into a relationship—this change in testosterone levels is no longer apparent.[53] Men who produce less testosterone are more likely to be in a relationship[54] or married,[55] and men who produce more testosterone are more likely to divorce;[55] however, causality cannot be determined in this correlation. Marriage or commitment could cause a decrease in testosterone levels.[56] Single men who have not had relationship experience have lower testosterone levels than single men with experience. It is suggested that these single men with prior experience are in a more competitive state than their non-experienced counterparts.[57] Married men who engage in bond-maintenance activities such as spending the day with their spouse/and or child have no different testosterone levels compared to times when they do not engage in such activities. Collectively, these results suggest that the presence of competitive activities rather than bond-maintenance activities are more relevant to changes in testosterone levels.[58]

Tribulus terrestris is an ingredient commonly presented as improving testosterone levels, but has not been found to be more effective than a placebo or possess any testosterone increasing properties. WebMD cautions that it interferes with Lithium and diabetes medications, and in general, not enough is known about tribulus terrestris to recommend a dosage for anyone.
Many studies demonstrate an improvement in mood of hypogonadal men treated with testosterone (Wang et al 1996; Azad et al 2003). The relationship between testosterone status and mood, particularly depression, remains unresolved. Using Beck’s Depression Inventory, Barrett-Connor and colleagues found that the depression score worsened as men aged, exactly at a time when testosterone levels are decreasing (Barrett-Connor et al 1999). Pope and colleagues found that testosterone treatment in men with refractory depression lowered the Hamilton Depression rating scale and the Clinical Global Impression severity rating (Pope et al 2003). The Beck Depression Inventory remained unchanged in Pope’s study.
Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.[77] The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.[77] Thus it is the challenge of competition among males of the species that facilitates aggression and violence.[77] Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.[77] The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males.[77]
A related issue is the potential use of testosterone as a coronary vasodilator and anti-anginal agent. Testosterone has been shown to act as a vasodilator of coronary arteries at physiological concentrations during angiography (Webb, McNeill et al 1999). Furthermore men given a testosterone injection prior to exercise testing showed improved performance, as assessed by ST changes compared to placebo (Rosano et al 1999; Webb, Adamson et al 1999). Administration of one to three months of testosterone treatment has also been shown to improve symptoms of angina and exercise test performance (Wu and Weng 1993; English et al 2000; Malkin, Pugh, Morris et al 2004). Longer term studies are underway. It is thought that testosterone improves angina due its vasodilatory action, which occurs independently of the androgen receptor, via blockade of L-type calcium channels at the cell membrane of the vascular smooth muscle in an action similar to the dihydropyridine calcium-channel blockers such as nifedipine (Hall et al 2006).
A loophole in FDA regulations allows pharmaceutical marketers to urge men to talk to their doctors if they have certain "possible signs" of testosterone deficiency. "Virtually everybody asks about this now because the direct-to-consumer marketing is so aggressive," says Dr. Michael O'Leary, a urologist at Harvard-affiliated Brigham and Women's Hospital. "Tons of men who would never have asked me about it before started to do so when they saw ads that say 'Do you feel tired?'"