Relationship Between Serum Testosterone, Digit Ratio And Body Composition Among Adolescents Of Igbo Ethnic Group In Nigeria
Digit ratio (2D:4D) is a sexually dimorphic trait, with females having a higher 2D:4D than males. This digit ratio has been associated with numerous behavioural traits and health conditions related to sex hormones. Four hundred and twelve secondary school students (209 males and 203 females) aged 12 to 20 years attending secondary schools within Enugu metropolis, in Enugu state, Nigeria participated in this work after an informed consent was obtained from them and their parents. Detailed information required from subjects was obtained through a standard designed questionnaire. Body fat percentage, weight (kg), Finger length (cm), height (cm), chest, waist and hip circumferences (cm) were measured using standard protocols. Body mass index (BMI), Waist to chest ratio (WCR) and Waist to hip ratio (WHR) were calculated. Blood sample for the estimation of testosterone was also obtained. The variables were studied according to sex and age groups. The data obtained was subjected to statistical analysis using SigmaStat 2.0 for Windows (San Rafael, CA) and statistical values were acceptable at p<0.05. Testosterone and all the anthropometric variables considered in this studyshowed statistical significant difference (p<0.001 and 0.002) between males and females. The result also indicated a negative significant relationship between 2D:4D of both hands and testosterone in males, while in females testosterone had a positive correlation with 2D:4D of the right hand and a negative correlation 2D:4D of the left hand (p<0.05). 2D:4D of both hands had a negative correlation with weight and height in females (p<0.01 and p<0.05) respectively while in males, 2D:4D did not correlate with height and weight (p>0.05). Males had a significant relationship with weight, height, body fat percentage and chest circumference (p<0.01) while in females testosterone had a significant relationship with weight, body mass index, body fat percentage, waist to hip ratio, chest, waist and hip circumference (p<0.05). In conclusion, the present study confirmed the existence of sexual dimorphism of finger lengths and digit ratios as well as in body composition variables. It also showed a relation between digit ratios and testosterone in the adolescent age group. These findings could be of importance in addressing biological traits and health conditions related to sex hormones.
There are very few parts of the human body in health or disease that provide observation better than the hand. The hand presents excellent opportunities for us, students of human nature and of human anatomy to exercise power of observation and to study the outward form of a portion of the body (Jones, 1942). But more to our purpose is the fact that in probing deeper into the anatomy of the hand we are immediately brought face to face with some of the most important biological problems and some of the most striking exhibitions of general vital principles. The fingers in the adult human hand differ in length and in distal extent (Jones, 1942). These finger lengths are fixed for life within the first three months of pregnancy (Manning et al., 1998;Csathoet al., 2003). Contemporary anthropological studies have found that in the clear majority of males, the distal extent of the ring finger tends to be relatively greater (using the middle finger as standard) than the index finger (Manning et al., 1998; McFadden and Shubel, 2002). However, the results for females vary considerably with some studies reporting that females show a similar pattern to that of males (Manning et al., 1998) while others suggest that the prevalence of a longer index finger is relatively or absolutely more common in females (Danborno et al.,2008a). This shows that the ratio of the index finger (2D) to that of the ring finger (4D) in humans is sexually dimorphic (Ecker, 1875; George, 1930; Phelps, 1952; Manning, 2002). This sexual dimorphic trait is also found in bonoboos (Ecker, 1875; Jones, 1942; Manning et al; 2003; Danborno et al., 2008a).
Finger length ratio is historical to what went on in the womb at the time when the brain, heart and other organs were growing (Malaset al., 2005; Mclntye, 2005 and Danbornoet al., 2008b). It suggests that a relatively long ring finger is a sign that certain organs were exposed to higher levels of testosterone while a relatively long index finger points to lower level of male hormone and higher levels of oestrogen (Manning et al., 2003 and Danborno et al., 2008a). Exactly how testosterone affects the foetal digit ratio is not clear. One theory is that for a certain time in foetal development, the ring finger which has more testosterone receptors than the index finger tends to grow faster when exposed to higher levels of the hormones (Zheng and Cohn, 2011). The patterns of activation of these receptors differ between sexes and affect the growth of specific digits. Androgen receptors appear around the 8th week of gestation and by the 14th week they have disappeared. It may be that there are more receptors on the ring finger than the index finger. Interestingly, when the back of the fingers are observed, it seems that there are more hairs on the middle part between the two joints of the ring finger than other fingers. This discovery provides a genetic explanation for a raft of studies that link finger digit ratio with traits ranging from sexual dimorphism (Ecker, 1875; George, 1930; Phelps, 1952;Manning, 2002),sperm counts(Manning et al., 1998), aggressions(Danborno et al., 2008b),sports prowess (Neave et al., 2003), eating disorders in women (Klumpet al., 2006) to other health related conditions such as cancers and heart related diseases (Manning,2002).
There are insufficient studies available on other digit ratios such as 3D:5D, 2D:5D and 3D:4D. Links between the developmental control of the urogenital system and patterns of finger growth may influence digits other than 2D and 4D (Manning et al., 2003). In humans, sexual dimorphism has been reported for 2D:5D and 3D:4D (McFadden and Shubel, 2002) and for 2D:3D and 2D:5D and this sex differences are greater in the right hand than the left hand (Manning et al., 2003). In mice, there is also evidence that 2D:3D is dimorphic (Kyriakidis and Papaioannidou, 2008). This may mean that otherdigit ratios could be correlated to sex-dependent traits such as developmental disorders and susceptibility to disease (example, 2D:3D, 2D:4D and 2D:5D for myocardial infarction (Manning et al., 2003). The stability of these ratios in rapidly growing children is therefore of interest. Adolescence is a dynamic period of development marked by rapid changes in body size, shape and composition, all of which are sexually dimorphic (Alan et al., 2002). These changes are as a result of rise in sex steroid secretion. Testosterone is well known for its role during this pubertal period. It promotes the development of secondary sexual characteristics such as growth spurt, increased muscle, bone-mass, the sprouting of body hair (Bassilet al., 2009), breast development, deposition of fat and development of sexual libido (Rakoet al., 1996) in females, thickening of the vocal chords and increase in strength in males. In addition, testosterone is essential for health and well-being of the body (Tuck and Francis 2009).
Body fat distribution is also sexually dimorphic and while the dimorphism in body fat is minimal in infancy, childhood and old age, it is maximal during early reproductive life mediated by sex steroids in combination with heritable genetic factors (Nelson et al., 1999). During puberty, males deposit adipose (and also muscle) tissue around the upper body whilst females deposit adipose tissue around the thighs and buttocks. This distribution of body fat is thought to signal the ratio of pubertal/adult oestrogen to testosterone, since the predominance of oestrogen at puberty produces a typical female body shape (gynoid), while the predominance of testosterone produces a typical male (android) body shape (Bjorntrop, 1997). It is commonly accepted that pubertal/adult sex hormones are the main regulators of sexually dimorphic physical features (Fink et al., 2003). If so, then there should be an association between sexual dimorphism determined in utero and other sexually dimorphic traits which are largely determined at puberty.
1.2 STATEMENT OF RESEARCH PROBLEM
There is accumulating evidence that 2D:4Dwhich is largely determined in-utero, increases with age and is sexually dimorphic (Manning et al., 1998; Malaset al., 2005; McIntyre et al., 2005; Triverset al., 2006 and Galiset al., 2009). Thus males tend to show lower values of 2D:4D than do females; that is males have on average longer fourth digits relative to their second than females (Phelps, 1952 and Manning et al., 1998). It has been suggested that sex differences in 2D:4D arise from in-utero concentration of sex steroids with 2D:4D negatively related to prenatal testosterone and positively associated with prenatal oestrogen (Manning et al., 1998). These sex differences in 2D:4D are robust across a number of ethnic groups and races (Manning et al., 1998). Considering certain problems associated with development of secondary sexual characteristics in adolescents, its relationship with prenatal exposure tosex hormones will be of great interest in medical field. Although the sexual dimorphism in 2D:4D is largely determined in utero, its relationship with sexual dimorphic traits at puberty is not clear. Similarly, data on the relationship between testosterone, digital ratio and body composition among Nigerians are scanty.
1.3 JUSTIFICATION OF THE STUDY Determining the relationship between serum testosterone, digit ratio (2D:4D) and body composition among adolescents could be of importance in the psycho-social management of this group of individuals. This could therefore improve the understanding of the physical changes that occur in the body during adolescence and could help parents and guardians in guiding this group of individuals during this critical period of life.
1.4 RESEARCH HYPOTHESES The following hypotheses have been formulated to guide the conduct of this study.
i. There is a correlation between serum testosterone level and body composition for an individual.
ii. There is a correlation between serum testosterone level and digit ratio (2D:4D).
iii. There is a correlation between 2D:4D and body composition variables.
iv. There is a relationship between digit ratio (2D:4D) and age of menarche in females.
1.5 SIGNIFICANCE OF STUDY This study will provide a reference value on sexual dimorphism of 2D:4D and other digit ratios among the Igbo ethnic group since Manning et al. (2003) reported significant ethnic variations in digit ratios (Gwunireama and Ihemelandu, 2010).It will provide an insight on the possibility of using anthropometric measurements and body composition assessment as predictor of risk of diseases in adults. May be useful in predicting behaviour of individuals and thus guide them towards a definitive career.
1.6AIMS AND OBJECTIVES OF THE STUDY
1.6.1 Aim The aim of this study was to determine the relationship between serum testosterone, digit ratios and body composition among adolescents in Igbo ethnic group. 1.6.2 Objectives The objectives of the present study shall be as follows:
i. Determine the relationship between digit ratio (2D:4D) and serum testosterone in adolescents.
ii. Determine the relationship between digit ratio (2D:4D) and body composition variables in adolescents
iii. Determine the relationship between serum testosterone and body composition variables in adolescents
iv. Determine the relationship between digit ratio (2D:4D) and age of menarche in females.
1.7. LIMITATIONS OF THE STUDY
i. The present study was limited by
ii. Inability of the subjects to fill out the questionnaires correctly.
iii. Difficulty in collecting blood samples twice (am and pm) from participants since assessment of androgen status is based on more than a single measurement (Braunstein, 2002).