From the publication:
Many factors, including external, environmental and internal factors, influence testosterone levels. The impact of energy intake derived from a testosterone-boosting diet depends on a human body mass. In the case of people of healthy body mass, insufficient energy intake may result in a reduction in testosterone levels in men. The same energy deficit in obese people, may, in turn, result in a neutral or positive impact on the levels of the hormone. Undoubtedly, nutritional deficiency, and particularly of such nutrients as zinc, magnesium, vitamin D, together with low polyphenols intake, affects the HPG [hypothalamic–pituitary–gonadal] axis. The levels of mental and oxidative stress can also adversely impact the axis. The higher the cortisol levels in a human body, or the higher its daily fluctuation, the lower the testosterone levels. What is more, the effect seems to be strengthened by excessive body weight, which is related to the increased oxidative stress affecting the functions of the Leydig cells. Other factors which might disrupt testosterone synthesis may be the length and quality of sleep. Even though the issue is relatively unknown, it appears that both sleep deprivation (shorter than five hours) and low quality of sleep (sleeping with the light on, sleeping during the day, under the influence of alcohol) impact the testosterone levels negatively.