What is Testosterone? 
Testosterone is the primary male hormone that stimulates the advancement of secondary sexual characteristics in men such as increased bone mass, muscle mass and hair growth. Apart from sexual characteristics, it also aids in general well-being.  Higher levels of testosterone not only improves body composition but also the quality of life. 



Symptoms of low testosterone 
Erectile Dysfunction(ED)-problem maintaining or having an erection
Loss of hair
Difficulty sleeping
Decreased energy or feeling fatigue
Increased body fat(generally around the lower belly for men)
Mood swings

What Causes a decline in Testosterone in Young Men 
Excessive drinking of alcohol
Abusing illegal drugs and anabolic steroids
Excessive masturbation
High level of cholesterol and blood pressure

The low activity of testicles can also be inherited trait or gotten through illnesses or accident.

The inherited conditions are:

Undescended testicles: at times, the testicles may not descend from abdomen before birth.

Klinefelter’s syndrome:  this is an instance whereby a man is born having the common sex chromosomes, for example, X, X OR Y.

Hemochromatosis: this is a condition whereby your body has so much iron in the blood which leads to testicular failure or damage in the pituitary glands.

Various damages happen on the testicles leading to low testosterone which include:

An injury physically on the testicles:  an injury on the testicles may cause low levels of testosterone
Mumps orchitis:  mumps infection is likely to lead to injuries on the testicles.

Treatment of cancer: chemotherapy and other radiations can cause damage to the testicles.

Additionally, low levels of testosterone may be a cause resulting from damage in the hypothalamus or the pituitary glands since it is the part of the brain responsible for production and control of hormone by the testes. Inherited conditions such as: may cause this

Pituitary disorders result from small tumors, drug abuse or kidney failure.

Kallmann syndrome: this is a condition abnormally related to hypothalamus functioning.

Inflammatory diseases, for instance, tuberculosis can impact negatively on the hypothalamus and the pituitary glands.

What Can You Do Naturally to Help Boost Testosterone?
There are several natural ways you can employ to aid in improving the testosterone levels which include:

Minimizing or avoiding smoking, alcohol consumption, and masturbation
Exercise: Endurance training as well as resistance training, for instance, weight lifting is known to boost testosterone levels to some extent. For example, physical activity such as Olympic lifts, bench presses, and squats are ideal for use. 
Healthy eating: There are several foods recommended for substantial improvement on the testosterone levels in the body. The foods with the potential to improve the testosterone level include natural compliments such as tuna which is rich in vitamin D. Other foods include milk containing low-fat content but containing vitamin D. Certain foods such as the egg yolk, fortified cereals, milk, oysters and shellfish contain vitamin D. 
Sleeping: Testosterone rises during sleep and starts to decline during waking hours. Therefore getting enough of quality sleep will ensure the body produces testosterone efficiently. Studies have proven that sleep restriction in men reduces the level of testosterone. 
Use of supplements: It is recommended to seek doctor’s approval before consuming supplements but testosterone boosters, according to BroScience, help prepare the body for the anabolic state. It plays a significant role in improving the levels of testosterone in the body.

References:

  "Testosterone - Wikipedia." https://en.wikipedia.org/wiki/Testosterone. Accessed 9 Jan. 2019.
  "Testosterone and weight loss: the evidence - NCBI - NIH." 28 Aug. 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4154787/. Accessed 9 Jan. 2019.
  "Low testosterone: 12 signs and symptoms - Medical News Today." 1 Aug. 2018, https://www.medicalnewstoday.com/articles/322647.php. Accessed 9 Jan. 2019.
  "Signs of Low Testosterone in Men Under 30 - Healthline." 29 Sep. 2016, https://www.healthline.com/health/low-testosterone/signs-men-under-30. Accessed 9 Jan. 2019.
  "Exercise and Testosterone Levels - WebMD." 6 May. 2015, https://www.webmd.com/men/features/exercise-and-testosterone. Accessed 9 Jan. 2019.
  "Low testosterone: 12 signs and symptoms - Medical News Today." 1 Aug. 2018, https://www.medicalnewstoday.com/articles/322647.php. Accessed 9 Jan. 2019.
  "Effect of 1 Week of Sleep Restriction on Testosterone Levels in Young ...." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4445839/. Accessed 9 Jan. 2019.