Digit ratio (2D:4D) and circulating testosterone, oestradiol, and progesterone levels across the menstrual cycle

Relationship between the 2D:4D and prenatal testosterone, adult level testosterone, and testosterone change: Meta-analysis of 54 studies

The ratio between the hands' second to the fourth finger (2D:4D) is commonly hypothesized to result from prenatal testosterone. The 2D:4D has also been hypothesized to relate to adult-level testosterone and, more recently, to the testosterone response to a challenging situation. In the present work, we tested these core assumptions. Drawing from, in total, 54 studies and 8077 participants, we investigated whether the 2D:4D is related to adult level testosterone (44 studies), testosterone change (6 studies), and prenatal testosterone (10 studies). We found no evidence of the relationship between the above testosterone types and digit ratios. Furthermore, there was no relationship between testosterone and the right and left 2D:4D, male and female 2D:4D, and the 2D:4D and testosterone measurement (i.e., measured in blood or saliva). However, we found some evidence that prenatal testosterone measured in amniotic fluid (but not cord blood) might be related to the digit ratios-further studies are necessary to validate this observation. In summary, considering the current state of knowledge, any conclusions drawn from the assumption of the digit ratios as the proxy for testosterone (prenatal, adult level, or testosterone change under a challenging situation) warrant great caution.

Are sex differences in blood cell count and hemoglobin moderated by the 2D:4D ratio? A cross-sectional study in a Ghanaian population

Background and Aims

There are sex differences in blood cell count and hemoglobin (HGB) in adulthood due to differences in the levels of circulating sex hormones. The second-to-fourth digit ratio (2D:4D) is the putative marker of prenatal hormone exposure. The 2D:4D or the right-left difference (Dr-l) are sexually dimorphic and are correlates of sex hormones in adulthood. The study sought to determine whether sex differences in adult blood cell count and HGB can be partly explained by the 2D:4D or Dr-l.

Methods

The study was cross-sectional between June and December 2021 at the University for Development Studies. The study involved 207 healthy participants (females = 113) aged from 18 to 32 years. The right-hand (2D:4DR), and the left-hand (2D:4DL) digit ratio and their difference (Dr-l) were measured using Computer-assisted analysis. Blood cell count, HGB, testosterone, and estradiol were measured from venous blood samples using an automated HGB analyzer and ELIZA technique.

Results

The platelet count was inversely related to the 2D:4DR in the total sample with the 2D:4DR accounting for about 0.2% (adjR 2 = 0.002) of the variability in platelet count. However, there was a sex difference as indicated by the significant interaction between sex and the 2D:4DR on platelet count (p = 0.03). The relationship between platelet count and the 2D:4DR was negative in females but positive in males. Also, there was a positive relationship between HGB concentration and the Dr-l in the total study sample, where the Dr-l accounted for about 0.6% (adjR 2 = 0.006) of the variability in HGB concentration. Sex interacted significantly with the Dr-l on HGB concentration (p = 0.01) such that the relationship between HGB and the Dr-l was positive in females but negative in males.

Conclusion

Prenatal hormone exposure, as indexed by the 2D:4D ratio, may partly account for the observed sex differences in platelet count and HGB levels in adulthood.

Dark Triad Personality Traits, Second-to-Forth Digit Ratio (2D:4D) and Circulating Testosterone and Cortisol Levels

INTRODUCTION

Dark Triad (DT) personality traits (psychopathy, Machiavellianism, and narcissism) show sex differences and associations with hormones. Understanding aetiology may assist in mitigating the harm of these potentially adverse characteristics. Low second-to-fourth digit ratio (2D:4D) is hypothesised to be a marker of high prenatal testosterone exposure and may provide important information about organisational hormones. The aim of the present study was to measure Dark Triad and Big 5 personality traits in relation to digit ratio, salivary testosterone, and cortisol.

METHODS

A non-clinical sample (N=268; 49.25% Female, age M25.20 ± 8.77yrs) completed the Short Dark Triad and International Personality Inventory Pool - Mini. Afternoon saliva was analysed for testosterone and cortisol, and 2D:4D finger ratios were measured.

RESULTS

Males scored higher on DT traits than females. Females scored higher on Big 5 agreeableness and neuroticism. Males had higher testosterone and cortisol levels and lower 2D:4D than females. Digit ratio correlated inversely with salivary testosterone, Machiavellianism, and psychopathy. Testosterone levels correlated positively with cortisol levels and psychopathy and negatively with agreeableness, neuroticism, and Machiavellianism.

CONCLUSIONS

These results provide indications that Machiavellianism and psychopathy (Dark Triad) traits, but not narcissism or Big 5 traits, are linked to markers of prenatal testosterone exposure. Results also replicate sex differences seen in 2D:4D digit ratios, with males having a shorter second-relative-to-forth finger. Links between circulating testosterone, digit ratios, cortisol and personality traits provide further information about potential biological bases of personality.

Sex-moderated relationship between the 2D:4D ratio and circulating hormones in an adult Ghanaian population

The second-to-fourth digit ratio (2D:4D) is the putative marker of prenatal hormone exposure. The 2D:4D ratio or the right-left difference (Dr-l) are said to be negative and positive correlates, respectively, of circulating testosterone and estrogen in both adult males and females. However, previous studies on the subject have reported mixed results. This study aimed to determine the sex-moderated relationship between the 2D:4D ratio and adult circulating testosterone, estradiol, testosterone-to-estradiol ratio and the free androgen index. This was a cross-sectional study from January to June 2021 at the University for Development Studies, Ghana. The study involved 62 participants (Female = 28; Male = 34), aged between 20 and 26 years. The right (2D:4DR), the left (2D:4DL), and their difference (Dr-l) were measured by computer-assisted analysis. Fasting venous samples were assayed for total testosterone (T), estradiol (E2 ), and sex hormone-binding globulin (SHBG) using ELISA. The free androgen index (FAI) was then calculated (T/SHBG) and the data were analyzed using moderated and/or weighted regression. Males had significantly higher T and FAI than females while females had significantly higher E2 than males, which were independent of age and body mass index (p < 0.001). There was a significant SEX*Dr-l interaction on FAI (p = 0.007). The Dr-l correlated negatively with FAI in males but positively in females and accounted for about 94.0% of the variability of FAI in males (adjR2  = 0.940) and only 0.2% in females (adjR2  = 0.002). The 2D:4D ratio, a putative marker of prenatal hormone exposure, may have an impact on sex differences in adult free androgen index.

Does sex interact with the 2D:4D ratio or adult circulating hormones on the estimated glomerular filtration rate? A cross-sectional study in Ghana

The 2D:4D ratio is the putative marker of prenatal hormone exposure and has been suggested as a correlate of adult circulating testosterone and estrogen. The study aimed to determine whether sexual dimorphism in the estimated glomerular filtration rate (eGFR) can be partly explained by the 2D:4D ratio or adult circulating testosterone or estrogen. The study was cross-sectional from June to December 2021 at the University for Development Studies. The study involved 206 healthy adults (Female = 93, Male = 113) between 18 and 30 years. The 2D:4D ratio was measured using computer-assisted analysis. Venous blood samples were collected and analyzed for testosterone, estradiol and creatinine using the ELISA technique and routine biochemical analysis. The adjusted eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation (2021). The eGFR and the testosterone-to-estradiol ratio (TT:E2 ) were significantly higher in males than in females (p < 0.001). There was a significant interaction between sex and the TT:E2 on the eGFR (p < 0.001). Although the relationship between the eGFR and the TT:E2 was negative in both males and females, a unit change in the TT:E2 had a greater impact on the eGFR in females (B = -1.38) than in males (B = -0.01). Sexual dimorphism in the eGFR is influenced by both testosterone and estradiol. Although the sex difference in the eGFR may be influenced by the TT:E2 , estrogen seems to account for more variability in the eGFR than testosterone.

An association between body image dissatisfaction and digit ratio among Chinese children and adolescents

Body image dissatisfaction (BID) is a negative evaluation of personal physical characteristics, including dissatisfaction with body shape, gender, sexual organs, appearance and so forth, and it plays an important role in growth and development. The second-to-fourth digit ratio (2D:4D) is recognized as a putative indicator of intra-uterine testosterone to estrogen ratio exposure, and it has been observed that higher levels of fetal testosterone exposure are associated with a lower 2D:4D. The present paper contributes to a better understanding of the biological underpinnings of BID by analyzing BID and the digit ratio (2D:4D). We found that the 2D:4D was positively related to appearance dissatisfaction in boys with first spermatorrhea, which means that low prenatal androgen exposure may increase boys’ dissatisfaction with their appearance. In girls with breast development being lower than Tanner stage II, their 2D:4D was negatively related to their body shape dissatisfaction, which means that high prenatal androgen exposure may increase girls’ dissatisfaction with their body shape. These results suggest that the prenatal androgen exposure level might play an important role in the body image dissatisfaction of the offspring.

Toxoplasma gondii and Psychopathology: Latent Infection Is Associated with Interpersonal Sensitivity, Psychoticism, and Higher Testosterone Levels in Men, but Not in Women

Objective

The ability of parasites to hijack the nervous system, manipulating the host’s physiology and behavior in ways that enhance the parasite’s fitness while damaging host fitness, is a topic of ongoing research interest in evolutionary biology, but is largely overlooked in mental health research. Nevertheless, recent evidence has shown that Toxoplasma gondii infection can change host testosterone levels and influence the development of some psychiatric disorders. Here, we tested this hypothesis in a mixed sample of 213 non-clinical subjects.

Methods

Participants (nmales = 108, nfemales = 105) provided 5 ml of blood to quantify testosterone levels and Toxoplasma gondii antibodies. The Symptom Checklist-90-Revised was used to assess psychopathological symptoms.

Results

The results showed that Toxoplasma-infected men had higher testosterone levels and scored higher in Interpersonal Sensitivity and Psychoticism symptoms than non-infected men. Toxoplasma-infected women did not differ from control women.

Conclusions

Framed in an evolutionary framework, the findings suggest that the elevated testosterone levels and the expression of psychopathological symptoms can be seen as the result of the manipulation exerted by Toxoplasma gondii either to reach its definitive host or to increase its spread. Future research can benefit from integrating insights from evolutionary biology and parasite-host interactions with physiology, immunology, and mental health to develop a better understanding of mental health etiology.

Season of birth and biomarkers of early-life environment

OBJECTIVE

Early-life conditions play an important role in human development, affecting health status and survival. Conditions in utero partly depend on the external environment and thus vary in relation to the season of birth. The aim of this study was to investigate if people born in different seasons of the year differ in values of biomarkers that reflect conditions during fetal development.

METHODS

The study was conducted among Polish rural women recruited at the Mogielica Human Ecology Study Site. The participants were 234 women aged 45 to 92 (mean = 60.2; SD = 10.44). The indicators of early-life environment analyzed in the study were: Absolute Finger Ridge Count (AFRC), the difference between mean number of ridge counts in both thumbs and both little fingers (Md15), overall facial fluctuating asymmetry (OFA), central facial asymmetry (CFA), right and left hand 2D:4D.

RESULTS

Values of biomarkers of fetal development did not vary among groups of women born in different seasons of the year.

CONCLUSIONS

Lack of differences in values of biomarkers according to birth season may indicate that: (a) season of birth is not a good indicator of early-life conditions; (b) tested biomarkers do not reliably reflect the prenatal environment; (c) season of birth does not fully overlap with the sensitive periods of biomarker development and thus fails to capture differences in developmental conditions.

No relationship between the digit ratios (2D:4D) and salivary testosterone change: Study on men under an acute exercise

The digit ratio (2D:4D) is said to be a potential marker of exposure to prenatal sex steroids. Some studies suggest that the 2D:4D is also linked with the testosterone response to challenging situations due to organizational effect of prenatal hormonal milieu on adult endocrine functioning. However, up to date, there were only four studies (conducted on small samples) that examined the 2D:4D and the testosterone response to a challenging situation (i.e. physical exertion or aggressive context). Here, we examined the relationship between the 2D:4D and the testosterone change under an acute exercise among 97 men. We found that the digit ratios (the right 2D:4D, the left 2D:4D, and the right minus left 2D:4D) were neither predictors of pre-exercise testosterone, nor the change in testosterone level after a cycling task. Our results add a contradictory to previous studies evidence in a discussion on the links of the 2D:4D and the testosterone change.

The association between second to fourth digit ratio, reproductive and general health among women: findings from an Israeli pregnancy cohort

The ratio between the length of second and fourth digits (2D:4D) is a putative biomarker for prenatal testosterone and estrogen exposure. The aim of the study was to examine the association between 2D:4D and women’s general and reproductive health. This analysis was conducted within a prospective pregnancy cohort study. The study population included 187 women. 2D:4D was measured directly in both hands using a digital caliper. Multivariable linear and logistic models were used to study the associations between digit ratio and the studied health characteristics. Mean age of the participants was 30.7 ± 4.9 years. The mean age at menarche was 12.9 ± 1.4 years. Right hand 2D:4D mean ± SD was 0.965 ± 0.03. Left hand 2D:4D mean ± SD was 0.956 ± 0.03. An association was found between right 2D:4D and age at menarche, with older age in women with 2D:4D ≥ mean versus 2D:4D < mean (13.2 ± 1.5 and 12.8 ± 1.3 respectively, b = 0.48, 95%CI:0.06–0.91) while controlling for ethnicity. Higher 2D:4D was also associated with heavier menses bleeding and dysmenorrhea. There is an association between 2D:4D and sub optimal reproductive characteristics, including later age at menarche, heavier menses bleeding and dysmenorrhea. These findings support the association between the intrauterine period and reproductive characteristics. Further studies are required to support our findings.

Body size measurements, digit ratio (2D:4D) and oestrogen and progesterone receptors' expressions in juvenile gigantomastia

Background Juvenile breast hypertrophy is characterised by massive enlargement of the breast in the peri-pubertal period. We aimed to analyse body size measurements (body mass index [BMI], waist-to-hip circumference ratio [WHR]), digit ratio (ratio of II and IV digits' length [2D:4D]) and oestrogen receptor (ER) alpha (ERα) and progesterone receptors (PRs) in the breast gland in women with juvenile gigantomastia. Methods The study involved 30 women (mean age 25.7 years) (mean age of onset - 14.8 years). ERα and PR expressions were detected immunohistochemically in breast gland samples. For comparison, 100 controls (50 women and 50 men) were included. Results BMI and WHR in women with gigantomastia were higher than in control women and the former had a higher WHR than expected for their BMI. 2D:4D in the examined women did not differ from that in control women. However, left 2D:4D was negatively related to the age of gigantomastia onset. There were no correlations between ER and PR expressions and the analysed body and digit ratios. Conclusions The lack of a relationship between 2D:4D and juvenile breast hypertrophy may suggest that foetal exposure to sex hormones may not be crucial in its aetiology. However, the link between high left 2D:4D and early development of gigantomastia suggests that prenatal sex hormones have a role in its development timing. High WHR, and particularly high WHR relative to BMI, may indicate that these women had at some stage of development higher circulating androgens, which may have been converted to oestrogens in breasts due to local aromatase activity. Verification of this hypothesis could allow consideration of the role of aromatase inhibitors in juvenile breast hypertrophy.

Revisiting the relationships of 2D:4D with androgen receptor (AR) gene and current testosterone levels: Replication study and meta-analyses

The relationships of digit ratio (2D:4D) with the length of AR (CAG)n, and testosterone levels from saliva and blood have been extensively debated over the years. This research including three studies further clarifies such controversies. To do so, we re-examined the relationships between the length of AR (CAG)n, 2D:4D, and current testosterone levels, through replication study and meta-analysis for each study. The results indicate: (a) the length of AR (CAG)n is not significantly associated with 2D:4D; (b) current testosterone levels are not significantly associated with the ratio; and (c) the length is not significantly associated with testosterone levels. Thus, AR (CAG)n and current testosterone levels are not significantly related to 2D:4D at individual level.

The digit ratio (2D:4D) relationship with testosterone is moderated by physical training: Evidence of prenatal organizational influences on activational patterns of adult testosterone in physically-active women

BACKGROUND

The 2nd to 4th digit ratio (2D:4D) is regarded as a sexually dimorphic trait governed by prenatal testosterone (T) and estradiol exposure. However, relationships between the 2D:4D and adult sex hormone concentrations are inconsistent in females. Environmental contingencies (e.g., physical training) may provide a stronger basis for establishing these linkages, particularly if the relationships are plastic and not fixed.

AIMS

To investigate associations between 2D:4D, training hours and salivary T (sal-T) measures in physically-active women.

STUDY DESIGN

Descriptive and quasi-experimental monitoring across the follicular (day 7), ovulatory (day 14) and luteal (day 21) phases of three menstrual cycles.

SUBJECTS

35 naturally-cycling women training regularly for sport (range 3-12 h a week).

OUTCOME MEASURES

Morning sal-T concentrations and changes in sal-T to a physical and psychological stimulus (~10 min) were measured.

RESULTS

Both 2D:4D and training hours were related to morning sal-T concentrations in all three menstrual phases (p < 0.01) and their interaction was significant during ovulation. Follow-up testing revealed a negative 2D:4D and sal-T association in women reporting high, but not low, training hours each week. Participant 2D:4D was also related to sal-T changes under physical and/or psychological challenge across each menstrual phase (p < 0.01), whereas training hours and its interaction with 2D:4D were not significant predictors of these outcomes.

CONCLUSIONS

2D:4D linkages with basal and challenge-induced sal-T changes were identified in women undertaking regular physical training. Training hours also moderated the 2D:4D link to morning sal-T, but with some menstrual-phase dependency. These complexities and environmental relationships may help reconcile conflicting results.

Relationship between the Second to Fourth Finger Length Ratio and Calcaneus Quantitative Ultrasound

This study aimed to characterize the relationship between the ratio of the length of the second and fourth fingers (2D:4D value) and the speed of sound of the calcaneus by quantitative ultrasound (QUS-SOS) in undergraduate female students. We recruited 138 young women with a mean age of 19.6 ± 1.4 years. The participants' calcaneus QUS-SOS was measured using an ultrasound bone densitometer. We also measured the participants' weight, height, and grip strength. A self-reported questionnaire was used to obtain information on participants' secondary sexual characteristics, and exercise habits. The present study showed that the 2D:4D value of both hands was significantly correlated with the calcaneus QUS-SOS. The 2D:4D value of the left hand was also positively associated with the calcaneus QUS-SOS results in several respects. These findings suggest that the 2D:4D value may be useful for the screening of risk for a low bone quality in undergraduate female students.

Do skin and hair pigmentation in prepubertal and early pubertal stages correlate with 2D:4D?

OBJECTIVES

In most human populations women are less pigmented than men. However, before puberty, boys tend to have lighter skin than girls. Previous research has shown that skin pigmentation in European women is negatively correlated with digit ratio (2D:4D). Therefore, it has been hypothesized that skin pigmentation in females is partially controlled by prenatal hormones. The aim of this study was to examine the correlation between 2D:4D and pigmentation in girls and boys in the prepubertal or early pubertal stages of ontogenesis.

METHODS

The study group consisted of 598 Polish children (275 boys), aged 6.5-10.5 years. All underwent spectrophotometric measurements of skin and hair melanin index (SMI and HMI) and had the second and the fourth finger on both hands measured directly.

RESULTS

SMI (in girls) and HMI (in girls and boys) were positively correlated with age but 2D:4D was not. We regressed SMI and HMI on age and used the residuals as a measure of age-independent pigmentation. In girls, positive correlations were found between resSMI and 2D:4D for the right hand, but there was no correlation with left 2D:4D. In boys, resSMI did not correlate with 2D:4D. The resHMI was not related to 2D:4D in girls or boys.

CONCLUSION

Skin pigmentation in prepubertal or early pubertal girls is related to 2D:4D such that high 2D:4D is associated with higher pigmentation. This relationship may be mediated by the individual rate of sexual maturation.