Testosterone in the body is either "free" or "bound." Free testosterone is also known as circulating testosterone. Free testosterone levels generally decrease with age and may have functions that relate to your physiological and psychological health. A study published in the "Journal of Cardiac Failure" suggests that free testosterone levels may relate to exercise capacity. The study suggests that men with chronic heart failure and lower levels of free testosterone have higher exercise intolerance.
Neurological Issues
Free testosterone may have neurological functions that counter the effects of degenerative diseases like Alzheimer's. A press release by the National Institute on Aging indicates that older men with lower levels of free testosterone may have a higher risk of developing Alzheimers disease. The press release refers to a study in which a 50 percent increase in free testosterone levels corresponded to approximately a 26 percent reduction in the risk of developing Alzheimer's. According to the Institute, older men with higher levels of circulating free testosterone perform special tasks better and have better visual and verbal memory.
Mobility
Free testosterone may have functions related to physical mobility. A study published in "The Journal of Clinical Endocrinology and Metabolism," suggests that free testosterone levels are associated with mobility limitation and physical performance in men that live in old-age communities. The results of the study indicate that increasing levels of continuous free testosterone were associated with lowering the risk of mobility limitation, and that men with low free testosterone levels were 57 percent more likely to report incidents of mobility limitation. The researchers concluded that lower levels of free testosterone are associated with a higher risk of incident mobility limitation and worsening mobility limitation in community-dwelling older men.
Reproductive Functions
Free testosterone in men may have reproductive functions related to sperm health. A study published on the Informa Healthcare website investigated the relationship between free testosterone and fertility. The study revealed that increasing free testosterone levels affected the concentration and motility of sperm cells. The study concluded that increasing free testosterone levels with a surgical procedure known as "varicocele litigation" improves the sperm concentration and motility in infertile men.
Aggression
According to a study published on the International Scientific Networks and Government Learning Policy Science website, circulating or free testosterone levels may have a causal relationship to aggressive behavioral responses in human males. The study suggests that free testosterone levels during the fetal stage of human development have organizational effects on the male brain, which include increasing readiness to engage in aggressive behavior. The results of the study indicate that higher free testosterone levels in adolescent human males may have a direct causal influence on aggressive response behavior when provoked. The researchers concluded that circulating or free testosterone levels may influence the strength or intensity of aggressive behavior during and perhaps even after puberty.
References
- National Institute on Aging: Low Free Testosterone Levels Linked to Alzheimer's Disease in Older Men
- The Journal of Clinical Endocrinology and Metabolism: The Framingham Offspring Study
- Informa Healthcare: Variococele Ligation on Free Testosterone
- Policy Science: Circulating Testosterone Levels and Agression
