Is Testosterone Genetic? Inherited Factors That Matter

Testosterone plays a crucial role in numerous bodily functions, influencing everything from muscle mass to mood. While lifestyle factors like diet and exercise impact hormone levels, genetics significantly determine individual testosterone production.

Understanding the genetic components behind testosterone provides insight into why levels vary between individuals and how inherited traits influence hormone regulation.

Genetic Influences On Testosterone Levels

Testosterone levels result from a complex interplay of genetic factors regulating hormone synthesis, metabolism, and signaling. Variations in genes involved in steroidogenesis—the biochemical pathway responsible for testosterone production—can lead to significant differences in hormone levels. One of the most studied genes in this process is CYP17A1, which encodes an enzyme critical for converting cholesterol into androgen precursors. Polymorphisms in this gene have been linked to variations in testosterone concentrations, with some alleles associated with higher or lower production rates. Similarly, mutations in HSD3B2, which encodes an enzyme necessary for converting precursors into active androgens, can alter testosterone synthesis, sometimes leading to clinical conditions such as congenital adrenal hyperplasia.

Beyond biosynthesis, genetic differences in testosterone metabolism contribute to individual variability. The SRD5A2 gene encodes 5-alpha reductase, an enzyme that converts testosterone into dihydrotestosterone (DHT), a more potent androgen. Variants in this gene influence the balance between testosterone and DHT, affecting traits such as hair growth, prostate health, and muscle development. Additionally, genes involved in testosterone clearance, such as UGT2B17, determine circulating hormone levels. Individuals with deletions in UGT2B17 exhibit reduced testosterone excretion, leading to higher serum concentrations, which has implications for both natural hormone regulation and anti-doping testing in sports.

The genetic basis of testosterone levels extends beyond individual genes to broader heritability patterns observed in twin and family studies. Research published in the Journal of Clinical Endocrinology & Metabolism estimates that genetic factors account for approximately 50–60% of the variation in testosterone levels among men. Genome-wide association studies (GWAS) have identified multiple loci associated with testosterone regulation, including variants near SHBG, which encodes sex hormone-binding globulin. SHBG influences the bioavailability of testosterone by binding to it in the bloodstream, and genetic differences in SHBG expression can lead to variations in free testosterone levels, which are more biologically active than total testosterone.

Hormone Receptor Variations

Testosterone’s effects depend not only on its production and metabolism but also on how cells respond to it, which is governed by androgen receptors (AR). These receptors, encoded by the AR gene on the X chromosome, mediate testosterone’s influence by binding to it and DHT. Once activated, the receptor complex translocates to the cell nucleus, regulating genes involved in muscle development, bone density, and secondary sexual characteristics. Variations in the AR gene significantly alter receptor sensitivity, leading to differences in how individuals respond to the same circulating testosterone levels.

One of the most well-documented variations in AR is the number of CAG repeats within its coding sequence. These repeats influence receptor function, with shorter CAG repeat lengths generally associated with greater androgen sensitivity and longer repeats linked to reduced receptor activity. Studies published in The Journal of Clinical Endocrinology & Metabolism show that men with shorter CAG repeats exhibit stronger androgenic effects, such as increased muscle mass and lower body fat percentages, even when their total testosterone levels are comparable to those with longer repeat sequences. Conversely, individuals with extended CAG repeats may experience diminished androgenic responses, which has been implicated in conditions like androgen insensitivity syndrome and variations in prostate cancer risk.

Beyond CAG repeat length, single nucleotide polymorphisms (SNPs) within the AR gene also contribute to receptor function diversity. Certain SNPs have been linked to differential transcriptional activity, affecting how efficiently the receptor binds to testosterone and initiates gene expression. Research in Nature Reviews Endocrinology highlights that specific variants modify androgen receptor signaling strength, influencing traits such as hair growth patterns, libido, and behavioral tendencies. These genetic differences may explain why some men experience stronger anabolic effects from testosterone, while others require higher hormone levels to achieve similar physiological outcomes.

Polymorphisms Affecting Regulatory Pathways

Testosterone regulation involves a network of genes controlling hormone synthesis, transport, and signaling, with polymorphisms in these regulatory pathways contributing to individual differences in circulating levels. One of the most influential regulatory genes is SHBG, which determines how much testosterone remains bioavailable. Variants in SHBG can alter its binding affinity, affecting the proportion of free testosterone available to interact with androgen receptors. GWAS have identified SNPs near SHBG that correlate with lower protein expression, leading to increased levels of unbound testosterone and potentially amplifying androgenic effects on muscle growth and metabolism.

Beyond transport mechanisms, polymorphisms in genes encoding enzymes responsible for hormone biosynthesis exert significant influence over testosterone availability. The CYP19A1 gene, which encodes aromatase, plays a role in converting testosterone into estrogen. Variants in this gene can lead to altered enzyme activity, impacting the balance between androgens and estrogens. Some polymorphisms result in increased aromatase expression, hastening testosterone conversion and reducing androgenic effects. This has been observed in conditions such as age-related hypogonadism, where elevated aromatization contributes to declining testosterone levels. Conversely, reduced aromatase activity can lead to excessive androgen accumulation, affecting reproductive and metabolic health.

Regulatory control also extends to genes involved in hypothalamic-pituitary-gonadal (HPG) axis signaling, the system governing testosterone production. The LHCGR gene encodes the receptor for luteinizing hormone (LH), a key regulator of testicular testosterone synthesis. Variants in LHCGR can affect receptor sensitivity, modifying the responsiveness of Leydig cells in the testes to LH stimulation. Certain polymorphisms have been linked to reduced receptor function, leading to lower testosterone production despite normal or even elevated LH levels. These genetic differences may contribute to conditions such as primary hypogonadism, where testosterone deficiency arises from impaired testicular function rather than inadequate hormonal signaling.

Inheritance Patterns

Testosterone levels exhibit a strong hereditary component, with twin and family studies revealing that genetic factors account for a significant proportion of individual variability. Research examining monozygotic and dizygotic twins estimates the heritability of testosterone levels to be between 50% and 60%, indicating that genetic inheritance plays a dominant role in determining baseline hormone concentrations. This genetic contribution is polygenic, meaning multiple genes collectively influence testosterone production, metabolism, and receptor sensitivity.

Parental influence on testosterone inheritance is complex due to the involvement of both autosomal and sex-linked genes. Unlike traits controlled by a single gene, testosterone regulation involves genes located on different chromosomes, including the X-linked AR gene, inherited maternally in males. Since men inherit only one X chromosome, variations in AR from their mothers exert a direct effect on androgen sensitivity. In contrast, genes involved in steroidogenesis, such as CYP17A1 and HSD3B2, follow Mendelian inheritance patterns, meaning mutations or polymorphisms in these genes can be passed down from either parent and contribute to familial trends in testosterone levels.

Environmental Interactions

While genetic factors establish a foundation for testosterone levels, environmental influences shape how these predispositions manifest. Lifestyle choices, exposure to endocrine-disrupting chemicals, and overall health play a substantial role in modulating hormone production and metabolism. Diet affects testosterone synthesis by providing essential nutrients such as zinc, vitamin D, and healthy fats, which are necessary for steroidogenesis. Studies show that individuals with balanced macronutrient intake and sufficient micronutrient levels tend to maintain higher testosterone concentrations. Similarly, resistance training and high-intensity interval training (HIIT) have been linked to acute increases in testosterone, although long-term effects vary based on age, genetics, and training intensity.

Environmental toxins can interfere with testosterone regulation by disrupting endocrine signaling. Chemicals such as bisphenol A (BPA), phthalates, and pesticides reduce testosterone levels by interfering with androgen receptor function or inhibiting steroidogenesis. Occupational exposures to heavy metals like lead and cadmium have also been associated with lower testosterone concentrations due to their toxic effects on Leydig cells, which produce testosterone in the testes. Chronic stress and poor sleep patterns contribute to hormonal imbalances by elevating cortisol levels, suppressing testosterone synthesis through feedback mechanisms in the HPG axis.

Genetic Testing Approaches

Advancements in genetic testing provide insights into individual variations in testosterone regulation. Direct-to-consumer genetic tests and clinical genomic analyses identify polymorphisms in genes related to steroidogenesis, androgen receptor sensitivity, and hormone metabolism. These tests examine variants in genes such as CYP17A1, SHBG, and AR, offering predictions about natural testosterone levels and potential responsiveness to hormonal changes.

Research utilizing GWAS has identified multiple loci associated with testosterone regulation, contributing to more targeted approaches in hormone therapy. However, the clinical utility of genetic testing for testosterone-related traits remains limited, as hormone levels fluctuate due to age, health status, and external factors. Future applications may provide more personalized approaches to optimizing testosterone levels based on an individual’s genetic profile.