Aging and androgens: Physiology and clinical implications

Sexual dissatisfaction and associated factors among middle-aged men-data from the Bavarian Men's Health study

BACKGROUND

Sexual satisfaction is a key aspect of overall well-being, and various factors-including low sexual frequency, poor communication, and societal sexual norms-can contribute to sexual dissatisfaction.

AIM

This study assesses the prevalence of sexual dissatisfaction in middle-aged men and explores its associations with different forms of sexual activity, perceived pressure with regard to sexuality of men, and the perceived importance of sexuality-factors that have been understudied in this population.

METHODS

Data were collected through the Bavarian Men's Health (BMH) Study using validated questionnaires and clinical interviews.

OUTCOMES

Sociodemographic, sexual behavioral, and psychological factors were analyzed using chi-square tests, with multiple logistic regression identifying predictors of sexual dissatisfaction.

RESULTS

Among 5,615 men, 54.6% reported sexual dissatisfaction. At the time of the survey, 86.9% were in a partnership, and 90.1% expressed satisfaction with their partnership. In the preceding 3 months, 84.4% reported partnered sexual activities. Sexual dissatisfaction was significantly associated with the absence of a stable partnership and lower frequency of various partnered sexual interactions (eg, vaginal, oral, anal, and partnered masturbation). Additionally, higher frequencies of solo masturbation and greater perceived pressure with regard to sexuality were associated with increased sexual dissatisfaction (all P < .05).

CLINICAL IMPLICATIONS

Medical interviews should address factors such as diverse forms of partnered sexual activity, perceived pressure with regard to sexuality and perceived importance of sexuality to identify contributors to sexual dissatisfaction effectively.

STRENGTHS AND LIMITATIONS

Strengths include large sample size and robust methodology. Limitations include the cross-sectional design and lack of data on sexual partners.

CONCLUSION

The findings highlight that over half of 50-year-old men report sexual dissatisfaction, emphasizing the importance of comprehensive sexual health assessments in clinical practice.

Testicular aging: mechanism, management and future therapy

Testicular aging results in degeneration in testicular function, including decreased testosterone production and quality of sperm. Decreased testosterone level is associated with a range of systemic diseases and comorbidities, including cardiovascular disease, cognitive decline, depression, osteoporosis, frailty, increased body fat, and metabolic syndrome. In addition, with the rapid development of industrialization and increasing environmental pollution, the quality of male semen continues to decline globally. Currently, the average age of first marriage and childbirth for men is delayed, and the birth rate has been declining year by year. At present, the therapies for testosterone level decline in clinical practice are relatively limited. Therefore, studying the triggering and delaying mechanisms of testicular aging is significant for improving male health and protecting male fertility. This review summarizes the mechanisms and treatment strategies for male reproductive aging.

Biochemical Hypogonadism in Aging Testicular Cancer Survivors: A Clinical Challenge

Background and objective

Few longitudinal studies have described the prevalence and development of biochemical hypogonadism in aging testicular cancer survivors (TCSs) in comparison to men from the general population (control subjects).

Methods

Serum total and free testosterone (Ttotal, Tfree) were measured in 593 TCSs median11 and 27 years after TC diagnosis (Survey-First; Survey-Last). Post-treatment adverse health outcomes (AHOs) were recorded. The results were compared to those in 578 control subjects. Treatment was stratified as surgery alone, radiotherapy alone, or platinum-based chemotherapy. Biochemical hypogonadism was defined as Ttotal <8 nmol/l, or as Ttotal <12 nmol/l and Tfree <225 pmol/l. We used multivariable logistic regression analysis to explore associations with age and treatment intensity. Statistical significance was set at p <0.05.

Key findings and limitations

Between the first and last survey the prevalence of biochemical hypogonadism increased from 12% to 41% in the TSC group and from 5% to 11% in the control group. Three decades after diagnosis, the probability of biochemical hypogonadism was significantly correlated with increasing age and greater treatment intensity. The combined age- and treatment- related probability of hypogonadism was more than threefold higher in the TCS group than in the control group. At the last survey, fewer eugonadal than hypogonadal TCS men reported at least one AHO attributable to androgen deficiency (54% vs 72%; p <0.001). Limitations include the availability of only one blood sample per survey wave.

Conclusions and clinical implications

For aging TCSs, the probability of biochemical hypogonadism depends on age and prior treatment intensity and is threefold higher than for control subjects at 30 yr after diagnosis. As late hypogonadism is associated with AHO incidence, the development of hypogonadism should be monitored via regular blood tests during TCS follow-up.

Patient summary

Depending on the treatment they received, older survivors of testicular cancer (TC) are at persistent risk of lower testosterone levels. Our study revealed low testosterone in 40% of TC survivors older than 60 years compared to 10% of similarly aged men from the general population. Low testosterone is associated with chronic conditions such as diabetes, fatigue, and/or erectile dysfunction. Testosterone should be regularly monitored during follow-up for TC survivors.

Hormones, Age, and Erectile Dysfunction: Should Routine Testing Be Part of the Initial Evaluation?

Background/Objectives: The aim of this study was to investigate the relationship between age, the severity of erectile dysfunction (ED), and the various hormones that may influence erectile function. Methods: A multicenter cross-sectional study was conducted between January 2015 and December 2023. The study assessed age, sexual function using the IIEF-15 questionnaire, and the levels of total testosterone (TT), free testosterone (FT), FSH, LH, estradiol, prolactin (PRL), and SHBG. Results: A total of 411 patients were included in the study. The mean age of the patients was 63.19 years. The vast majority (91.73%) exhibited some degree of ED. The severity of ED increases with age, ranging from 56.26 years for patients without ED to 73.12 years for those with severe ED. A statistically significant negative correlation was observed between IIEF and age, while a positive correlation was observed between IIEF and serum levels of TT and FT (p < 0.05). Age was significantly correlated with all evaluated hormones (p < 0.01), except estradiol and prolactin. Total testosterone levels progressively decreased with the increase in the severity of erectile dysfunction, from a median of 7.05 ng/mL in patients with normal erectile function to 3.56 ng/mL in those with severe symptoms, remaining above the normal minimum threshold across all groups, whereas free testosterone (FT) levels also declined progressively. All erectile dysfunction groups had median FT levels below the normal minimum threshold. FSH, LH, and SHBG showed an increase with each progressive severity of erectile dysfunction. The multivariate linear regression revealed that IIEF scores are significantly associated with age, TT, and FT levels, while FSH did not present a statistically significant association in this model. Conclusions: Age shows a significant statistical correlation with both the severity of erectile dysfunction and the levels of total testosterone, free testosterone, LH, FSH, and SHBG. Total and free testosterone levels are significantly associated with the severity of erectile dysfunction, with free testosterone median values remaining above the normal minimum threshold in all patients with erectile dysfunction. Therefore, free testosterone should be considered a routine test, alongside total testosterone. In contrast, LH, estradiol, SHBG, and prolactin do not demonstrate any statistical correlation with erectile dysfunction and should not be recommended as routine investigations.

Inter-organ communication is a critical machinery to regulate metabolism and aging

Inter-organ communication (IOC) is a complex mechanism involved in maintaining metabolic homeostasis and healthy aging. Dysregulation of distinct forms of IOC is linked to metabolic derangements and age-related pathologies, implicating these processes as a potential target for therapeutic intervention to promote healthy aging. In this review, we delve into IOC mediated by hormonal signaling, circulating factors, organelle signaling, and neuronal networks and examine their roles in regulating metabolism and aging. Given the role of the hypothalamus as a high-order control center for aging and longevity, we particularly emphasize the importance of its communication with peripheral organs and pave the way for a better understanding of this critical machinery in metabolism and aging.

The Influence of Trinucleotide Repeats in the Androgen Receptor Gene on Androgen-related Traits and Diseases

CONTEXT

Trinucleotide repeats in the androgen receptor have been proposed to influence testosterone signaling in men, but the clinical relevance of these trinucleotide repeats remains controversial.

OBJECTIVE

To examine how androgen receptor trinucleotide repeat lengths affect androgen-related traits and disease risks and whether they influence the clinical importance of circulating testosterone levels.

METHODS

We quantified CAG and GGC repeat lengths in the androgen receptor (AR) gene of European-ancestry male participants in the UK Biobank from whole-genome and whole-exome sequence data using ExpansionHunter and tested associations with androgen-related traits and diseases. We also examined whether the associations between testosterone levels and these outcomes were affected by adjustment for the repeat lengths.

RESULTS

We successfully quantified the repeat lengths from whole-genome and/or whole-exome sequence data in 181 217 males. Both repeat lengths were shown to be positively associated with circulating total testosterone level and bone mineral density, whereas CAG repeat length was negatively associated with male-pattern baldness, but their effects were relatively small and were not associated with most of the other outcomes. Circulating total testosterone level was associated with various outcomes, but this relationship was not affected by adjustment for the repeat lengths.

CONCLUSION

In this large-scale study, we found that longer CAG and GGC repeats in the AR gene influence androgen resistance, elevate circulating testosterone level via a feedback loop, and play a role in some androgen-targeted tissues. Generally, however, circulating testosterone level is a more important determinant of androgen action in males than repeat lengths.

Age-related testosterone decline: mechanisms and intervention strategies

Contemporary societies exhibit delayed reproductive age and increased life expectancy. While the male reproductive system demonstrates relatively delayed aging compared to that of females, increasing age substantially impacts its function. A characteristic manifestation is age-induced testosterone decline. Testosterone, a crucial male sex hormone, plays pivotal roles in spermatogenesis and sexual function, and contributes significantly to metabolism, psychology, and cardiovascular health. Aging exerts profound effects on the hypothalamic-pituitary-gonadal axis and Leydig cells, precipitating testosterone reduction, which adversely affects male health. Exogenous testosterone supplementation can partially ameliorate age-related testosterone deficiency; however, its long-term safety remains contentious. Preserving endogenous testosterone production capacity during the aging process warrants further investigation as a potential intervention strategy.

TRACK_9: Testosterone replacement assessment: Classical vs. functional hypogonadism-knowledge from a 9-year study

BACKGROUND AND OBJECTIVE

The longitudinal efficacy and clinical utility of Testosterone Therapy (TTh) in ameliorating functional hypogonadism (FH) remain contentious, with long-term data being scarce. To address this lacuna, a comprehensive long-term registry study, stratifying patients across a spectrum of hypogonadal etiologies, offers a robust investigative paradigm.

MATERIALS AND METHODS

This 9-year registry, encompassing 650 patients (equivalent to 4,362 cumulative years of treatment), included 188 patients diagnosed with FH (mean age 42.3 ± 11.3 years) and 462 individuals with classical hypogonadism (CH). The cohort segregated into 266 men with primary hypogonadism (PH, mean age 34.0 ± 11.7 years) and 196 with secondary hypogonadism (SH, mean age 31.9 ± 12.0 years). Uniform treatment across the cohort involved intramuscular administration of testosterone undecanoate (1,000 mg). A comparative analysis was conducted focusing on anthropometric, metabolic, and safety parameters.

RESULTS

Serum testosterone levels increased from 6.6 ± 2.4 to 19.3 ± 2.9 nmol/L (p < 0.001). TTh was linked with weight reduction and decreased waist circumference (WC) in both CH and FH cohorts (both p < 0.001). Cox regression and Kaplan-Meier analyses delineated disparities: men with FH demonstrated a higher propensity for losing > 10% body weight and > 5% WC compared to CH (hazard ratio [HR] 1.3 [1.1-1.4], p = 0.008 and HR 1.4 [1.3-1.5], p = 0.001). Increases in hematocrit > 50% were uniform across groups, albeit amelioration of anemia was more pronounced in FH versus CH (p = 0.002). Increments of prostate-specific antigen (PSA) levels were more likely to occur in FH (HR 1.3 [1.1-1.6], p = 0.003). FH patients exhibited pronounced improvements in metabolic parameters and in aging male symptom score (AMS) and IIEF-EF questionnaire scores. These effects were markedly modulated by age and initial weight. Subgroup analysis of age-matched obese patients revealed an accentuated impact of TTh in CH compared to FH.

DISCUSSION AND CONCLUSION

The therapeutic outcomes of TTh across distinct hypogonadal populations demonstrate heterogeneous responses, significantly influenced by diagnostic categorization, age, and baseline risk factor profiles.

Male Reproductive Endocrine Disorders

The endocrine system intricately regulates male sexual development and health which influences masculinization, sexual libido, muscle mass, bone density, and overall vitality. Disorders in the hypothalamic-pituitary-gonadal axis can lead to hypogonadism, gynecomastia, sexual dysfunction, and infertility. Testosterone replacement therapy can be considered for symptomatic hypogonadism but poses risks for azoospermia and polycythemia, along with uncertain impact on cardiovascular disease. Gynecomastia results from a high estrogen-to-androgen ratio, mostly from either excess estrogen or decreased androgens. Sexual dysfunction is more commonly secondary to psychological or metabolic disorders; consider workups to rule out endocrine etiologies including hypogonadism if indicated.

Dietary vitamin K intake in relation to skeletal muscle mass and strength among adults: a cross-sectional study based on NHANES

Background

Previous studies revealed that vitamin K might help maintain muscle homeostasis, but this association has received little attention. We aimed to explore the associations of vitamin K intake with skeletal muscle mass and strength.

Methods

We included cross-sectional data from the U.S. National Health and Nutrition Examination Survey (NHANES, 2011-2018). Vitamin K intake was assessed via 24-h recall. Covariate-adjusted multiple linear regression and restricted cubic splines were used to evaluate the associations of dietary vitamin K intake with skeletal muscle mass and strength, measured by dual-energy X-ray absorptiometry and handgrip dynamometer, respectively.

Results

Dietary vitamin K intake was positively associated with skeletal muscle mass in males (β = 0.05747, p = 0.0204) but not in females. We also revealed a positive association between dietary vitamin K intake and handgrip strength within the range of 0-59.871 μg/d (P nonlinear = 0.049). However, beyond this threshold, increasing vitamin K intake did not cause additional handgrip strength improvements.

Conclusion

We provided evidence for a positive relationship between dietary vitamin K intake and skeletal muscle mass in males. Moreover, our study revealed a nonlinear relationship between dietary vitamin K intake and handgrip strength, highlighting an optimal intake range.

Testosterone therapy in older men: clinical implications of recent landmark trials

Testosterone therapy for men with hypogonadism due to identifiable hypothalamic-pituitary-testicular (HPT) pathology is uncontroversial. However, the risks and benefits of testosterone for men with clinical features of hypogonadism in the absence of identifiable HPT axis pathology have been uncertain. Recent landmark placebo-controlled trials assessed the benefits and risks of testosterone therapy (≤3 years) for middle-aged and older men with symptoms and possible signs of hypogonadism or end-organ androgen deficiency, low or low-normal serum testosterone concentrations, but no HPT pathology: Testosterone therapy (1) had modest-but clinically significant-benefits on average self-reported energy and mood, sexual function, and satisfaction; (2) in conjunction with a lifestyle programme, reversed or reduced incident type 2 diabetes mellitus (T2D) in men at high risk of or newly diagnosed with T2D; (3) modestly improved objectively assessed muscle strength and timed walking distance; (4) increased bone density and strength, but did not reduce falls or typical osteoporotic fractures and surprisingly increased the risk of fractures typically attributable to trauma; and (5) did not significantly increase the risk of myocardial infarction, stroke, or prostate cancer. These landmark trials help to inform clinical decision-making about testosterone therapy for men.

Androgens and erectile dysfunction: from androgen deficiency to treatment

INTRODUCTION

Androgens play important roles in regulating the growth and development of the male reproductive system and maintaining libido and erectile function. The specific mechanisms by which androgen deficiency leads to erectile dysfunction (ED) are not yet fully understood.

OBJECTIVES

To understand the mechanisms and treatment of androgen deficiency-related ED.

METHODS

A literature search in the past 10 years was conducted in PubMed and Google Scholar to determine the effects of androgen deficiency on erectile function and the treatment of androgen deficiency.

RESULTS

Androgen deficiency can be caused by hypothalamic-pituitary lesions and injuries, testicular-related diseases and injuries, endocrine and metabolic disorders, the side effects of medication, and age. Androgen deficiency can lead to ED by inhibiting the NOS/NO/cGMP pathway (nitric oxide synthase/nitric oxide/cyclic guanosine monophosphate) and altering the expression of ion channel proteins, as well as by inducing oxidative stress, death, and fibrosis in penile corpus cavernosum cells. Testosterone replacement therapy is effective at improving the serum testosterone levels and erectile function in patients with androgen deficiency. For patients who need to maintain a low androgenic state, erectile function can be improved by lifestyle changes, treatment with phosphodiesterase type 5 inhibitors, low-intensity extracorporeal shock wave therapy, and stem cell therapy.

CONCLUSIONS

Androgen deficiency can affect the structure and function of the penile corpus cavernosum, leading to ED. Areas of further study include how androgen replacement therapy can improve erectile function and how to improve the maintenance of erectile function in patients with hypoandrogenic status.

The Role of One-Carbon Metabolism and Methyl Donors in Medically Assisted Reproduction: A Narrative Review of the Literature

One-carbon (1-C) metabolic deficiency impairs homeostasis, driving disease development, including infertility. It is of importance to summarize the current evidence regarding the clinical utility of 1-C metabolism-related biomolecules and methyl donors, namely, folate, betaine, choline, vitamin B12, homocysteine (Hcy), and zinc, as potential biomarkers, dietary supplements, and culture media supplements in the context of medically assisted reproduction (MAR). A narrative review of the literature was conducted in the PubMed/Medline database. Diet, ageing, and the endocrine milieu of individuals affect both 1-C metabolism and fertility status. In vitro fertilization (IVF) techniques, and culture conditions in particular, have a direct impact on 1-C metabolic activity in gametes and embryos. Critical analysis indicated that zinc supplementation in cryopreservation media may be a promising approach to reducing oxidative damage, while female serum homocysteine levels may be employed as a possible biomarker for predicting IVF outcomes. Nonetheless, the level of evidence is low, and future studies are needed to verify these data. One-carbon metabolism-related processes, including redox defense and epigenetic regulation, may be compromised in IVF-derived embryos. The study of 1-C metabolism may lead the way towards improving MAR efficiency and safety and ensuring the lifelong health of MAR infants.

Testosterone therapy and the risk of cardiovascular disease in older, hypogonadal men

The debate over the cardiovascular (CV) implications of testosterone therapy (TT) have resulted in diverging safety recommendations and clinical guidelines worldwide. This narrative review synthesizes and critically evaluates long-term studies examining the effects of TT within the context of aging, obesity, and endogenous sex hormones on CV disease (CVD) risk to support informed clinical decision-making. Observational studies have variably linked low endogenous testosterone with increased CVD risk, while randomized controlled trials (RCTs) demonstrate that TT yields cardiometabolic benefits without increasing short-term CV risk. The TRAVERSE trial, as the first RCT powered to assess CVD events, did not show increased major adverse cardiac events (MACE) incidence; however, its limitations - specifically the maintenance of testosterone at low-normal levels, a high participant discontinuation rate, and short follow-up - warrant a careful interpretation of its results. Furthermore, findings from the TTrials cardiovascular sub-study, which showed an increase in non-calcified plaque, indicate the need for ongoing research into the long-term CV impact of TT. The decision to initiate TT should consider the current evidence gaps, particularly for older men with known CVD. The CV effects of maintaining physiological testosterone levels through exogenous means remain to be fully explored. Until more definitive evidence is available, clinical practice should prioritize individualized care and informed discussions on the potential CV implications of TT.

Single-cell transcriptomics identifies senescence-associated secretory phenotype (SASP) features of testicular aging in human

The male reproductive system experiences degradation with age, predominantly impacting the testes. Testicular aging can result in failure to produce physiological testosterone levels, normal sperm concentrations, or both. However, we cannot predict the onset of testicular aging in advance. Using single-cell RNA sequencing (scRNA-seq) from Gene Expression Omnibus (GEO) database, we conducted cell-cell communication network of human testis between older and young group, indicating Leydig cells' potential role in spermatogenesis microenvironment of aging testis. And we depicted the senescence-Associated Secretory Phenotype (SASP) features of aging testis by identifying differentially expressed senescence-associated secretory phenotype (SASP)-related genes between two group. Notably, IGFBP7 mainly expressed in Leydig cells of those differentially expressed SASP-related genes in aging testis. Furthermore, IGFBP7 protein located in the interstitial compartment of older mice confirmed by immunofluorescence and highly expressed in both human seminal plasma and mouse testis in the older group confirmed through Western blot. Together, our findings suggest that IGFBP7 may be a new biomarker of testicular aging.

Approach to the Patient: The Evaluation and Management of Men ≥50 Years With Low Serum Testosterone Concentration

Although testosterone replacement in men with classic hypogonadism due to an identified pathology of the hypothalamic-pituitary-testicular axis is uncontroversial, the role of testosterone treatment for men with age-related declines in circulating testosterone is unclear. This is due to the lack of large, long-term testosterone therapy trials assessing definitive clinical endpoints. However, men ≥50 years of age, particularly those who have a body mass index >25 kg/m2 and multiple comorbidities, commonly present with clinical features of androgen deficiency and low serum testosterone concentrations. Clinicians are faced with the question whether to initiate testosterone therapy, a difficult dilemma that entails a benefit-risk analysis with limited evidence from clinical trials. Using a case scenario, we present a practical approach to the clinical assessment and management of such men.

Understanding the age-related alterations in the testis-specific proteome

INTRODUCTION

Fertility rates in developing countries have declined over the past decades, and the trend of delayed fatherhood is rising as societies develop. The reasons behind the decline in male fertility with advancing age remain mysterious, making it a compelling and crucial area for further research. However, the limited number of studies dedicated to unraveling this enigma poses a challenge. Thus, our objective is to illuminate some of the upregulated and downregulated mechanisms in the male testis during the aging process.

AREAS COVERED

Herein, we present a critical overview of the studies addressing the alterations of testicular proteome through the aging process, starting from sexually matured young males to end-of-life-expectancy aged males. The comparative studies of the proteomic testicular profile of men with and without spermatogenic impairment are also discussed and key proteins and pathways involved are highlighted.

EXPERT OPINION

The difficulty of making age-comparative studies, especially of advanced-age study subjects, makes this topic of study quite challenging. Another topic worth mentioning is the heterogeneous nature and vast cellular composition of testicular tissue, which makes proteome data interpretation tricky. The cell type sorting and comorbidities testing in the testicular tissue of the studied subjects would help mitigate these problems.

T-score discordance between hip and lumbar spine: risk factors and clinical implications

Background

T-score discordance is common in osteoporosis diagnosis and leads to problems for clinicians formulating treatment plans.

Objectives

This study investigated the potential predictors of T-score discordance and compared fracture risk among individuals with varying T-score discordance status.

Design

This was a single-center cross-sectional study conducted at Wan Fang Hospital, Taipei City, between 1 February 2020 and 31 January 2022.

Methods

The present study enrolled patients aged ⩾50 years who received advanced bone health examination. Participants with a history of fracture surgery or underlying musculoskeletal diseases were excluded. Bioelectrical impedance analysis and dual-energy X-ray absorptiometry were used to determine the body composition and T-score, respectively. Discordance was defined as different T-score categories between the lumbar spine and hip. The impact of discordance on an individual's fracture risk was assessed using the Fracture Risk Assessment Tool (FRAX).

Results

This study enrolled 1402 participants (181 men and 1221 women). Of the 912 participants diagnosed with osteoporosis, 47 (5%) and 364 (40%) were categorized as having major and minor discordance, respectively. Multinomial logistic regression revealed that decreased walking speed was significantly correlated with major discordance but not osteoporosis in both the hip and lumbar spine (odds ratio of 0.25, p = 0.04). The adjusted FRAX scores for the major osteoporotic fracture risks of the major and minor discordance groups were approximately 14%, which was significantly lower than that of people having osteoporosis in both the hip and lumbar spine.

Conclusions

Walking speed exhibited the most significant correlation with major discordance in patients with osteoporosis. Although adjusted major fracture risks were similar between the major and minor discordance groups, further longitudinal studies are warranted to confirm this finding.

Registrations

This study was approved by the Ethics Committee of Taipei Medical University on 01/04/2022 (TMU-JIRB N202203088).

Alterations in Pregnenolone and Testosterone Levels in Male Shift Workers

Steroid hormone levels are closely related to the endogenous circadian rhythm induced by sleep-wake and dark-light cycles. Shift work that disrupts the circadian rhythm may influence the levels of steroid hormones. The association between shift work and alterations in female sex steroid hormone levels has been studied, but little is known about testosterone and its precursor pregnenolone levels in male shift workers. The present study investigated serum pregnenolone and testosterone levels in a group of shift and daytime male workers. All participants were sampled at the beginning of the morning shift. Lower levels of serum pregnenolone and total testosterone were found in the shift workers compared to the daytime workers. Variations in pregnenolone levels may have consequences for well-being, and they might produce consequences for the levels of hormones downstream of the steroid hormone cascade, such as testosterone. The low levels of testosterone found in shift workers demonstrate the perturbative effect of shift work on testosterone serum levels, which may be independent and/or related to pregnenolone synthesis.