Nigerian Journal of Basic and Clinical Sciences

: 2018  |  Volume : 15  |  Issue : 2  |  Page : 127--131

Effects of urbanization on digit length, second-to-fourth digit ratio (2D:4D), and blood pressure among the hausa ethnic group of Kano, Nigeria

Abdullahi Y Asuku1, Barnabas Danborno2, Shehu A Akuyam3, James A Timbuak2, Lawan H Adamu1,  
1 Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University, Kano, Kano State, Nigeria
2 Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Sciences, Ahmadu Bello University, Zaria, Nigeria
3 Department of Chemical Pathology, Faculty of Allied Health Sciences, College of Health Sciences, Ahmadu Bello University, Zaria, Nigeria

Correspondence Address:
Dr. Abdullahi Y Asuku
Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University, Kano, P.M.B. 3011, Kano State


Background: Urbanization and its attendant lifestyle modifications have been shown to affect body compositions, anatomical variables, and phenotypes, and body composition and phenotypes are important determinants of blood pressure. The present study aimed at investigating the effect of urban dwelling on digit length, second-to-fourth digit ratio (2D:4D), and blood pressure in a sample of urban and rural population of Hausa ethnic group in Kano, Nigeria. Materials and Methods: The study design was cross-sectional and included 465 (266 males and 199 females) persons of Hausa ethnic group residing in Kano. The mean age was 34.4 years for males and 32.0 years for females. Systematic random sampling technique was employed for subject recruitment. Height, weight, digit lengths, and digit ratios were obtained using standard anthropometric techniques. Blood pressure was measured following standard clinical procedure. Results: The results showed that both systolic and diastolic components of blood pressure were significantly higher in urban than in rural participants. While the length of the ring (4th) finger was significantly higher in the rural participants, there was no statistically significant rural–urban difference in the length of the index (2nd) digit. 2D:4D was significantly lower in the rural than in urban participants. The rural–urban difference in the digit ratio was more marked in the male participants than in females and more marked in the right hand than left hand. Conclusion: Diastolic and systolic components of blood pressure are significantly higher in the urban participants. Urban–rural difference in 2D:4D was observed among Hausa population.

How to cite this article:
Asuku AY, Danborno B, Akuyam SA, Timbuak JA, Adamu LH. Effects of urbanization on digit length, second-to-fourth digit ratio (2D:4D), and blood pressure among the hausa ethnic group of Kano, Nigeria.Niger J Basic Clin Sci 2018;15:127-131

How to cite this URL:
Asuku AY, Danborno B, Akuyam SA, Timbuak JA, Adamu LH. Effects of urbanization on digit length, second-to-fourth digit ratio (2D:4D), and blood pressure among the hausa ethnic group of Kano, Nigeria. Niger J Basic Clin Sci [serial online] 2018 [cited 2019 Jan 24 ];15:127-131
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Urbanization is documented to be strongly associated with lifestyle changes such as physical inactivity, consumption of high fat and low fiber diet,[1],[2],[3] and increased psychological stress.[3] These urban–rural differences in lifestyle are said to account for variations in body composition, body sizes, and phenotypes,[4],[5] as well as higher urban prevalence of hypertension and other cardiometabolic risk indicators.[4],[5],[6],[7] The ratio of the second-to-fourth digit is an attractive subject currently receiving attention from investigators.[8],[9],[10] The ratio of 2nd and 4th fingers (2D:4D) is determined and transmitted through genetic inheritance and is related to prenatal exposure to testosterone.[11] Research has shown that from the moment this anthropometric characteristic is determined during the 13th– 14th week of intrauterine life,[12] it does not change either in the adolescent period or in adulthood.[13]

2D:4D digit ratio is regarded as a physiological marker for the prenatal concentrations of the sex hormones, testosterone and estrogen, which organize the architecture of the body and the brain and the distribution of hormone receptors.[14] Digit ratio has been associated with many biological traits including the in utero levels of testosterone, aggression, behavior, spatial ability, and academic performance.[12],[15],[16],[17],[18],[19],[20] Some disease conditions such as autism, depression and developmental psychopathology, congenital adrenal hyperplasia, and polycystic ovarian syndrome are also correlated with digit ratio.[21],[22] 2D:4D also correlates with body size and composition indices such as body mass index (BMI), chest circumference,[23] waist circumference (WC), waist-to-hip ratio (WHR),[24],[25] neonatal birth weight,[26] and hypertension.[27] Earlier reports showed that 2D:4D might be affected by ethnicity [28],[29] and latitude of the study area.[30] These studies have shown that the ethnic variation in the ratio is far greater than the difference between the sexes. In addition to the significant sexual dimorphism in 2D:4D, the mean digit ratios varied between the English, Scottish, Uygur, Han, and Jamaican children.[28] Another study on the pediatric age group showed higher ratios among the Caucasians when compared to the Blacks and the Hans ethnicity of China.[31]

The established relationship of 2D:4D with body traits such as BMI, WC, WHR, and hypertension and the reports that these traits are significantly higher in urban than rural dwellers [4],[32],[33],[34] led to our hypothesis in this study that urbanization significantly affects digit length, digit ratio, and blood pressure. Therefore, this study was conducted to test this hypothesis.

 Materials and Methods

Study setting and population

Systematic random sampling technique was employed in selecting 465 original Hausas of Kano based on a history of at least two parental generation being Hausas from Kano. Urban and rural dwellers were defined based on self-reported history of being born in the urban or rural settlement and perpetual habitation in the same environment for at least a decade. Participants were recruited from outpatient units of Murtala Muhammad Specialist Hospital, Khadija Memorial Hospital and the old campus of Bayero University, Kano as urban participants and from Sule Uran Clinic Gabasawa, General Hospital Dawakin–Tofa as rural participants. The average distance between the urban Kano metropolis and the selected rural settlements is approximately 60 km. The study only included individuals in the age range of 18 years to 68 years. Patients with congenital and/or acquired digit deformity and those on antihypertensive medications were excluded. Ethical approval was obtained from Kano State Hospitals Management Board, and written informed consent was obtained from the participants. Height was measured to the nearest 0.1 cm as the vertical distance between the standing surface and the vertex of the head while the subject was standing erect in the Frankfort plane and without shoes using a stadiometer. The weight was measured in kg using a digital weighing scale while the subject was wearing light clothes.

Digit length measurements

Digit lengths was measured on the ventral surface of the hand from the midpoint of the basal crease of the digit to the tip of the finger using a digital sliding caliper (MicroMak, USA) measuring to 0.01 mm and reported on a questionnaire. This measurement has been reported to have a high degree of repeatability.[35],[36]

Measurement of blood pressure

A mercury sphygmomanometer was used for measuring blood pressure. Two measurements were taken, and at least 2 min were allowed between readings. The diastolic pressure was read at the level when sound disappeared (Korotkoff phase V), whereas the systolic one was read at the level when it appeared. The brachial artery was the site of auscultation. Participants were asked to refrain from smoking or ingesting caffeine for 30 min before measurement and the measurement was taken after at least 5 min of rest.[37]

Statistical analyses

The data were expressed as mean ± SD. Student's t-test was used to compare the parameters of male and female urban and rural participants. SPSS version 20 (IBM Corporation, NY) statistical software was used for statistical analyses and P < 0.05 was set as the level of significance.


Descriptive statistics for age, blood pressure, digit lengths, and 2D:4D participants are shown in [Table 1].{Table 1}

[Table 2] shows that combined male and female DBP and SBP were significantly higher in urban than rural dwellers (P < 0.01). The length of the ring finger was significantly (P < 0.05) longer in rural participants while there was no significant difference (P > 0.05) in the length of the index fingers. 2D:4D was significantly higher in both left (P < 0.05) and right (P < 0.01) hands of urban participants.{Table 2}

[Table 3] shows that both DBP and SBP were observed to be significantly higher in male urban dwellers (P < 0.01). The length of the ring finger was significantly (P < 0.01) longer in the rural participants whereas there was no significant difference (P > 0.05) in the length of the index finger. 2D:4D was significantly higher in both left (P < 0.05) and right (P < 0.01) hands of the urban male participants than in rural male participants.{Table 3}

[Table 4] that shows that both DBP and SBP were significantly higher in female urban than that in rural dwellers (P < 0.01). The left and right 2D:4D ratios were significantly higher (P < 0.05) in urban female participants than in rural female participants.{Table 4}


It is a well-established concept that 2D:4D once established in utero around the 14th–15th week of gestation remains fairly stable throughout life;[11],[13] however, it is not immediately clear why 2D:4D in this study was observed to be significantly higher in urban than in rural participants. It is, however, possible that certain environmental factors peculiar to urban or rural settlements actually influence the embryonic development of the digit resulting in the formation of urban or rural 2D:4D variant that manifest in later life. This impression is strengthened by reports in the literature where 2D:4D is documented to vary due to environmental influence.[30] Furthermore, many body traits which were reported to be strong correlates of 2D:4D such as body adiposity indices (BMI, WC, WHR)[23],[24],[25] and blood pressure [27] were similarly reported to be significantly higher among urban dwellers when compared to rural settlers.[4],[6],[33] This may partly explain why 2D:4D was observed to be higher in the urban dwellers of the present study. In addition, the embryonic development of digit length and digit ratio has been linked to HoxA and HoxB genes as key players.[38],[39] These genes are responsible for sexual differentiation in the developing embryo and by extension the production of sex hormones (testosterone and progesterone), which in turn determines the digit length, and thus, the digit ratio.[38],[39]

The tendency to have a high blood pressure and to accumulate excessive body fat indicated by BMI, WC, and WHR like 2D:4D has genetic susceptibility,[40],[41] and since testosterone, the principal determinant of digit length and digit ratio plays a role in body fat distribution,[42] it can be speculated that certain environmental factors peculiar to urban or rural dwelling may enhance the formation of a genetic variant manifesting morphologically in the digit ratio and body adiposity measures and functionally in the blood pressure. This may lend support to the observation in this study that 2D:4D and blood pressure were significantly higher among the urban participants.

In the present study, the urban–rural difference in 2D:4D was observed to be stronger in the right compared with the left hand and was also observed to be stronger in males compared with females. The reason for this asymmetry and sexual dimorphism is also unclear but could be related to the handedness of the participants. However, in support of this observation, development of digit ratio is reported to be a function of androgen sensitivity related to X-linked androgen receptor gene on the digit rather than the androgen concentration.[20] If the alleles in the androgen receptor (AR) genes have more CAG, then it makes the AR gene insensitive to the testosterone while it is compensated by producing more testosterone in the embryo.[20] It is possible that these androgen receptors are unevenly distributed with a higher concentration on the right hand which may still be a pointer to the influence of handedness in the asymmetry observed. In support of this study, Oyeyemi et al.[24] reported that the correlation of right 2D:4D with other measures of body adiposity was stronger when compared to the left. This is also in agreement with some previous studies.[43] Right hand 2D:4D is believed to be a better predictor of intrauterine testosterone levels.[43],[44] Thus, sex difference in the right hand 2D:4D is more pronounced than that in the left hand. Invariably, the right hand shows stronger correlation with predicted variables than that of the left hand.[44]

The higher male predilection in the effect of urbanization on digit length and digit ratio observed in this study may not be unconnected with exposure of males to a higher androgen concentration levels in utero. This view is supported by the observation in this study that there was a significant urban–rural difference in the length of the ring (4th) finger, which is the main site of action of testosterone in the developing fetal digit.[44]

The observed higher mean value of both systolic and diastolic components of blood pressure in urban compared with rural participants of this study is in keeping with earlier reports. Sabir et al.[33] conducted a study on a rural and urban settlement in Nigeria and showed that the mean values of DBP and SBP were higher for urban inhabitants. In addition, Adediran et al.[32] conducted an observational study on rural and urban settlements of Abuja, Nigeria to compare the distribution of MetS parameters among the people in both communities and found that DBP and SBP were significantly lower in rural settlements. This finding may also be related to the fact that urban participants might be less active and consume unhealthy food containing more saturated fat and high calorie diet, whereas rural participants eat the traditional high carbohydrate low protein and low fat diet, as documented in the literature.[3] These lifestyle changes of urban dwellers are associated with increased body adiposity, insulin resistance, and the consequential cardio-metabolic derangement which includes hypertension.

The findings of this study suggest that 2D:4D probably has urban and rural variants. This may be of immense significance to the forensic anthropologist as it offers 2D:4D as a simple and easily measurable complementary forensic tool that could give a clue about the domicile of an individual, especially when other body parts apart from the hands are mutilated beyond identification. The rural–urban difference in the mean blood pressure observed in this study is an indirect means of quantifying the adverse cardio-metabolic effect of urbanization on the urban communities of Kano, and therefore, provide the basis for creating awareness by health authorities.


It can be concluded from the result of this study that 2D:4D, diastolic, and systolic components of blood pressure are significantly higher in urban than rural dwellers in Kano. The urban–rural difference in 2D:4D is more pronounced in the right than the left hand and in males than in females.

Financial support and sponsorship

This work is an extract of a Ph.D. dissertation which was sponsored by Tertiary Education Trust Fund (TETfund) of Nigeria.

Conflicts of interest

There are no conflicts of interest.


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