The Link Between Parkinson’s Disease and Testosterone

Overview of the Endocrine System

endocrine glands

The endocrine system is composed of glandular tissues

The endocrine system is composed of glandular tissues that produce and secrete chemical messengers in the form of hormones that communicate with virtually every system of the human body.  These hormones number more than 30 and together they exert influence over processes including human growth, maturation, appetite, male or female reproduction, etc.  Many hormones are most frequently associated with athletic performance; however, their influence extends well beyond performance enhancing effects…most importantly their effect upon the human nervous system.

Overview of Parkinson’s Disease


Parkinson’s Disease is a disorder that initially affects the motor or movement functions

Parkinson’s Disease is a disorder that initially affects the motor or movement functions that are controlled by the nervous system.  The disease typically is associated with older age groups with men be affected slightly more frequently than women are.  Initial symptoms are subtle and include shakiness, shuffling gait (walking) or tremors and weakness (motor activity symptoms) but as the disease progresses speech, mood disorders including anxiety and depression, and disorders of thinking, memory, and concentration (non-motor activity symptoms) often occur.  While not life threatening, this disease can be debilitating, causing significant disability and distress for someone afflicted.  This disease is progressive and without treatment, an individual can suffer for many years.

Historically many causes have been investigated including environmental toxins and other substances foreign to the human body.  Specifically, carbon monoxide, pesticides, certain street drugs, certain medications (in particular antipsychotics), free radicals, and exposures to metals such as lead and those used in industrial or welding occupations have all been associated with the development of Parkinson’s Disease.


Reduction in a critical brain hormone called dopamine can cause symptoms consistent with Parkinson’s Disease

Heredity or genetics have been implicated in the development of some cases of Parkinson’s Disease but this pathway is less significant than the pathways or causes noted above.  What we do know definitively is that a reduction in a critical brain hormone or neurotransmitter called dopamine can cause symptoms consistent with Parkinson’s Disease.  We also know that Parkinson’s Disease occurs more frequently in men and those individuals with a history of head injury are more likely to develop Parkinson’s Disease.  We also know that age plays a significant role with most cases occurring over the age of 60.  In fact, approximately 1% of individuals over the age of 60 have symptoms consistent with Parkinson’s Disease.

Overview of Testosterone

Testosterone is a hormone most typically associated with males however; it is present throughout the lifespan in both men and women although in significantly higher levels in males.  Testosterone plays a vital role in sexual development and arousal, development of muscle, energy levels, and mood.  This vital role is mediated via the pituitary gland (chief controller of all endocrine gland activities) located in part of the brain.

As noted above, the endocrine system is complex and two-way communication between the endocrine system and the nervous system occurs through a variety of messenger chemicals including dopamine.  A review of the complex relationship between these two systems is beyond the scope of this article but it is important to understand that communication between these systems occurs and that this communication occurs both ways with the endocrine system directing certain nervous system functions and vice versa.  For example, as dopamine levels (neurotransmitter) increase, testosterone (endocrine hormone) levels increase with the pituitary gland in the brain directly exerting influence on the production and release of prolactin (another endocrine hormone).  This is a simple explanation of the pathway but helps to understand the reciprocal (but complex) relationship that occurs.

The Science behind the Relationship between Testosterone and Parkinson’s Disease

If Parkinson’s Disease (and Parkinsonian symptoms) occurs when levels of dopamine decrease then any environmental or hormonal influences that reduce dopamine may precipitate the onset of symptoms.  More recently, scientists have conducted numerous experiments to test this relationship.  This experimentation has occurred in part because anecdotally low levels of testosterone were demonstrated in many patients suffering with Parkinson’s Disease.  In particular, rapidly decreasing levels of testosterone in men demonstrates a strong link to the onset of Parkinson’s Disease symptoms although even individuals experiencing predictable decreases in testosterone levels that occur during the aging process are not spared from developing the disease.  This precipitated much scientific inquiry and to date numerous scientists have noted this heretofore-unrecognized link between low testosterone levels and Parkinson’s Disease in both humans and animals.  In science, replication of scientific findings is critically important to make certain that the findings are accurate.  Scientists have been able to replicate this link repeatedly.

Treatment of Parkinson’s Disease

If you recall the complex relationship between the nervous system and the endocrine system then it would be logical to predict that increasing the levels of testosterone in men who demonstrate symptoms of Parkinson’s Disease would lessen the disease symptoms.  This is true.  Initially, scientists and physicians noted a decrease in non-motor Parkinson’s Disease symptoms, but more recently, testosterone replacement therapy has demonstrated improvement in both non-motor symptoms and in motor function symptoms.  These improvements have been noted when all other known treatments for Parkinson’s Disease in these individuals have failed to provide relief in either symptom group.  These findings of improvement in both symptom groups have also been replicated repeatedly.

What does this all mean to men suffering with Parkinson’s Disease symptoms?  It means first that a relationship between a neurologist and an endocrinologist will be instrumental in gathering history and other data (including other factors that may be contributing to symptom onset) and to obtaining and interpreting an individual’s testosterone levels, (numerous tests over time may be necessary).  Once obtained, if a deficiency of testosterone is noted, then the relationship between that particular individual’s Parkinson’s Disease symptoms and testosterone level must be evaluated prior to initiating treatment.

If treatment is recommended, then most likely it will be in the form of testosterone replacement therapy (often a gel) that is applied to the skin or more rarely the testosterone replacement will be administered via intramuscular injections.  Follow up testing of testosterone levels will need to occur to make certain that the dosage of testosterone being administered is adequate.  At the same time, various tests of motor function and non-motor function will need to occur to evaluate the effect of the replacement therapy.  This is extremely exciting news for men suffering with the disease.  As yet, the relationship between women with the disease and testosterone (or other endocrine hormones more common in women such as estrogen) is still being investigated scientifically but discovering this link between low testosterone levels and Parkinson’s Disease symptoms in men has precipitated much scientific research into the complex relationship between the nervous system and the endocrine system.