From a cellular level, testosterone is a key hormone in male biology. It is responsible for a man's ability to reproduce and characterises muscle and bone mass, facial hair and sexual function. Testosterone production increases during puberty, however typically declines from the age of 30 years old.
Red light therapy shows great promise as a natural and safe form of treatment to boost testosterone levels. Before we dive into the benefits of RLT, lets investigate why increasing these levels is so important for optimal health.
So, what is testosterone?
Testosterone is a hormone produced by the human body. It’s mainly produced in men by the testicles. A man's appearance and sexual development is all influenced by Testosterone. It stimulates sperm production and sexual function. It also helps build muscle and bone mass.
The Problem with Decreased Testosterone
A range of symptoms can occur if testosterone production drastically drops below normal. These include:
Research suggests that the level of testosterone begins to drop for men around the age of 30. . Some contributing factors to a decline in testosterone include a lack of sleep, poor nutrition, a sedentary lifestyle and stress.
Red Light therapy also known as low-level laser therapy or photobiomodulation, uses concentrated wavelengths of light to increase energy production.
Red and NIR light wavelengths have been shown to stimulate energy production within the Leydig cells. The Leydig cells are responsible for producing testosterone in the testicles. Enhanced energy production in your cells is believed to help naturally increase testosterone production. This powerful effect on the body’s mitochondria has been shown in hundreds of clinical studies.
Sperm motility is also associated with cellular energy. The more energy, the stronger the sperm will swim. This is incredibly important in reproductive health, and vital in improving sperm motility.
Let’s check out some of the most recent clinical trials that show the benefits red light therapy has on testosterone production.
Increased Sex Drive
A group of researchers from the University of Siena, led by Dr. Andrea Fagiolini conducted a placebo-controlled pilot study in 2016 to ascertain the impact of Red Light Therapy in the increment of testosterone in men with low sexual desire.
For the purpose of the study, they gathered 38 men with low sex drive and divided them into two groups, with one receiving clinical doses of the Red Light Therapy at dawn, and the other going along with the control measure.
In the end, the light therapy group’s testosterone level grew from 2.1 ng/ml to about 3.6 ng/ml within two (2) weeks. 
Dr. Andrea Fagiolini, the leader of The Italian Pilot research group concluded that the Red Light Therapy boosted the sexual performance of the examined men by increases their testosterone. 
Boosts Male Fertility
With a reduction in sex drive, caused by reduced testosterone, research shows that Red Light Therapy helps increase the movement of spermatozoa (sperm motility) in male testes. RLT is a very effective physical therapy method and is recommended as an integral part of the complex treatment of infertility. RLT can significantly improve the survival, motility and speed of movement of spermatozoa. [4, 5, 6, 7]
Further research such as that of a 2017 report published in Scientific Reports strongly recommended natural light for sperm motility because they don’t pose oxidative DNA damage to the testes and sperm. 
Red Light Therapy on Mammals
This clinical trial was conducted to examine the effects of RLT on the testis in elevating serum T level in rats. The study used a 670-nm diode laser which was found to be effective in increasing serum T in the rats without causing any histopathological side effects.
In conclusion, the scientists believe that RLT may be a successful alternative treatment to the conventional types of testosterone replacement therapy . 
In 2013, another red light therapy laboratory research on mammals paved the way for the submission that red light therapy has a lot to offer in improving the testosterone levels of other mammals.
The report, which was published in the Nepal Medical College Journal stated that the two hormones that produce natural sex steroids and testosterone in mammals, which are the Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) were increased within a 70-day timeframe after the application of red light therapy. 
Researchers also studied the impact of natural light on boar sperm and the motility of dogs. The outcomes further laid credence to the established notion that red light therapy improves testosterone levels in both humans (males) and mammals. [11, 12]
Natural and Safe
The quest for a natural method of boosting testosterone has stemmed from the fact that most medications have side effects that are detrimental to patients’ health. Red light therapy is a natural therapy that is safe, painless and non-invasive. RLT has is shown to increase sperm motility and does not cause harm to the sperm or the testes.
These other natural remedies work extremely well when combined with daily Red Light Therapy sessions:
Resistance training is a fantastic way to increase testosterone. The more muscle mass built, the more your body stimulates the production of testosterone.
Eating a whole food diet rich in micronutrients. As the saying goes, you are what you eat. Packaged food and takeaway can interfere with the balance of sex hormones in the body.
Stress is a primary factor that contributes to many chronic diseases. Stress creates an overload of cortisol which causes an imbalance to hormonal system. Too much cortisol increases insomnia and imbalances your hormones. Managing stress is essential for optimal health. Meditation, yoga and relaxing hobbies are fantastic ways to decrease stress.
As shown in clinical trials and by numerous scientists, red light therapy naturally increases testosterone. As well as increasing testosterone, RLT also provides a wide range of health benefits to help optimise your health.