|Year : 2018 | Volume
| 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
|Date of Web Publication||14-Sep-2018|
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
Source of Support: None, Conflict of Interest: None
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.
Keywords: Blood pressure, digit length, digit ratio, Hausa ethnic group, urbanization
|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;15:127-31
|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 2022 Jan 25];15:127-31. Available from: https://www.njbcs.net/text.asp?2018/15/2/127/241152
| Introduction|| |
Urbanization is documented to be strongly associated with lifestyle changes such as physical inactivity, consumption of high fat and low fiber diet,,, and increased psychological stress. These urban–rural differences in lifestyle are said to account for variations in body composition, body sizes, and phenotypes,, as well as higher urban prevalence of hypertension and other cardiometabolic risk indicators.,,, The ratio of the second-to-fourth digit is an attractive subject currently receiving attention from investigators.,, The ratio of 2nd and 4th fingers (2D:4D) is determined and transmitted through genetic inheritance and is related to prenatal exposure to testosterone. Research has shown that from the moment this anthropometric characteristic is determined during the 13th– 14th week of intrauterine life, it does not change either in the adolescent period or in adulthood.
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. Digit ratio has been associated with many biological traits including the in utero levels of testosterone, aggression, behavior, spatial ability, and academic performance.,,,,,, Some disease conditions such as autism, depression and developmental psychopathology, congenital adrenal hyperplasia, and polycystic ovarian syndrome are also correlated with digit ratio., 2D:4D also correlates with body size and composition indices such as body mass index (BMI), chest circumference, waist circumference (WC), waist-to-hip ratio (WHR),, neonatal birth weight, and hypertension. Earlier reports showed that 2D:4D might be affected by ethnicity , and latitude of the study area. 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. Another study on the pediatric age group showed higher ratios among the Caucasians when compared to the Blacks and the Hans ethnicity of China.
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 ,,, 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.,
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.
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.
| Results|| |
Descriptive statistics for age, blood pressure, digit lengths, and 2D:4D participants are shown in [Table 1].
|Table 1: Descriptive statistics for age, blood pressure, digit length, and 2D:4D of participants|
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[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: Effect of urbanization on blood pressure, digit length, and 2D:4D of the combined male and female study populations|
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[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: Effect of urbanization on blood pressure, digit lengths, and 2D:4D of the males participants|
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[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: Effect of urbanization on blood pressure, digit length, and 2D:4D of the females participants|
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| Discussion|| |
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;, 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. Furthermore, many body traits which were reported to be strong correlates of 2D:4D such as body adiposity indices (BMI, WC, WHR),, and blood pressure  were similarly reported to be significantly higher among urban dwellers when compared to rural settlers.,, 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., 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.,
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,, and since testosterone, the principal determinant of digit length and digit ratio plays a role in body fat distribution, 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. 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. 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. 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. Right hand 2D:4D is believed to be a better predictor of intrauterine testosterone levels., 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.
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.
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. 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. 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. 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.
| Conclusion|| |
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.
| References|| |
Taro Y, Masahiro U, Ryutaro O, Influence of urbanisation on physical activity and dietary changes in Huli-speaking population: A comparative study of village dwellers and migrants in urban settlements. Br J Nutr 2001;85:65-73.
Nyenwe EA, Osaretin JO, Anele EI. Type 2 diabetes in adult Nigerians: A study of its prevalence and risk factors in Port Harcourt, Nigeria. Diabetes Res Clin Pract 2003;62:177-85.
Amuna P, Zotor FB. Epidemiological and nutrition transition in developing countries: Impact on human health and development. Proc Nutr Soc 2008;67:82-90.
Ekezie J, Anyanwu EG, Danborno B, Anthony U. Impact of urbanization on obesity, anthropometric profile and blood pressure in the Igbos of Nigeria. North Am J Med Sci 2011;3:242-6. [Full text]
Mbanya JC, Assah FK, Saji J, Atanga EN. Obesity and type 2 diabetes in Sub-Sahara Africa. Curr Diabetes Rep 2014;14:501.
Abubakari AR, Lauder W, Agyemang WC, Jones M, Kirk A, Bhopal RS. Prevalence and time trends in obesity among adult West African populations: A meta-analysis. Obes Rev 2008;9:297-311.
Ramachandran A, Mary S, Yamuna A, Murugesan N, Snehalatha C, High prevalence of diabetes and cardiovascular risk factors associated with urbanization in India. Diabetes Care 2008;31:893-8.
Putz DA, Gaulin SJC, Sporter RJ, McBurney DH. Sex hormones and finger length: What does 2D:4D indicate? Evol Hum Behav 2004;25:182-99.
Hone LSE, McCullough ME. 2D:4D ratio predict hand grip strength in (but not hand grip endurance) in men (but not in women). Evol Hum Behav 2012;33:780-9.
Manning T, Fink J, Trivers T. Digit ratio (2D:4D) and gender inequalities across nations. Evol Psychol 2014;124:757-68.
Umut H, Zeynep S, Özhan P, Ferdi G, Burak K, Hüseyin E. Relationship between second to fourth digit ratios and obesity, muscle mass. J Clin Anal Med 2015;10:4328-46.
Van Anders SM, Hampson E, Testing prenatal androgen hypothesis: Measuring digit ratios, sexual orientation and spatial abilities in adults. Horm Behav 2005;47:92-8.
Çelik A, Aksu F, Tunar M, Daşdan Ada EN, Topaçoğlu H. The relationship between the individual performance levels of master athletes and the finger ratios at hand. DEU Fac Med J 2010;24:5-10.
Manning JT, Bundredb PE, Newtonc DJ, Flanagan BF. The second to fourth digit ratio and variation in the androgen receptor gene. Evol Hum Behav 2003;24:399-405.
Lutchmaya S, Baron-Cohen S, Raggatt P, Knicmeyer R, Manning JT. 2nd
digit ratios, fetal testosterone and estradiol. Early Hum Dev 2004;77:23-8.
Bailey AA, Hurd L. Finger length ratio (2D:4D) correlates with physical aggression in men but not in women. Biol Psychol 2005;68:215-22.
Millet K, Dewitte S. Digit ratio (2D:4D) moderates the impact of an aggressive music video on aggression. Person Individ Differ 2007;43:289-94.
Manning JT. Digit ratio: A pointer to fertility, behavior and health. New Brunswick, NJ: Rutgers University Press; 2002.
Bull R, Benson P. Digit ratio (2D/4D) and the spatial representation of magnitude. Horm Behav 2006;50:194-9.
Romano M, Leoni B, Saino N. Examination marks of male university students positively correlate with finger length ratios (2D:4D). Biol Psychol 2006;71:175-82.
Catrall FR, Vollenhoven BJ, Weston GC. Anatomical evidence for in utero
androgen exposure in women with polycystic ovary syndrome. Fertil Steril 2005;84:1689-92.
Fink B, Manning JT, Williams JHG, Podmore-Nappin C. The 2nd
digit ratio developmental psychopathology in school-aged children. Person Individ Differ 2007;42:369-79.
Danborno B, Adebisi S, Adelaiye AB, Ojo S. Sexual dimorphism and relationship between chest, hip and waist circumference with 2D, 4D and 2D:4D in Nigerians. Inter J Biol Anthropol 2008;1:2.
Oyeyemi BF, Iyiola OA, Oyeyemi AW, Oricha KA, Anifowoshe AT, Alamukii NA. Sexual dimorphism in ratio of second and fourth digits and its relationship with metabolic syndrome indices and cardiovascular risk factors. J Res Med Sci 2014;19:234-9.
Oyeyemi BF, Adebayo JO, Anifowoshe AT, Iyiola OA. Relationship between ratio of second and fourth digit and obesity traits among different ethnic groups in Ilorin, North Central Nigeria. Not Biol Sci 2016;8:396-400.
Danborno B, Adebisi SS, Adelaiye AB, Ojo SA. Relationship between digit ratio (2D:4D) and birth weight in Nigerians. Anthropology 2010;12:127-30.
Ravinder KY, Manju B. A study of 2nd
digit ratio (2D:4D) in relation to hypertension in north Indian males and its implications for risk factors in coronary heart disease. Indian J Clin Anat Physiol 2016;3:24-6.
Manning JT, Stewart A, Bundred PE, Trivers RL. Sex and ethnic differences in 2nd
digit ratio of children. Early Hum Dev 2004;80:161-8.
Manning JT, Churchill AJG, Peters M. The effects of sex, ethnicity and sexual orientation on self-measured digit ratio (2D:4D). Arch Sex Behav 2007;36:223-33.
Loehlin JC, McFadden D, Medland SE, Martin NG. Population differences in finger-length ratios: Ethnicity or latitude? Arch Sex Behav 2006;35:739-42.
Jacob M, Avadhani R, Nair B, Nallathamby R, Soman MA. Cross sectional study of second and fourth digit ratio with physical attributes in South Indian population. Int J Anat Res 2015;3:1133-7.
Adediran O, Akintunde AA, Edo AE, Opadijo OG, Araoye AM, Impact of urbanization and gender on frequency of metabolic syndrome among native Abuja settlers in Nigeria. J Cardiovasc Dis Res 2012;3:191-6.
Sabir AA, Isezuo SA, Ohwovoriole OA, Fasanmade SA, Iwuala AS, Umar MT. Rural-urban difference In plasma lipid levels and prevalence of dyslipidemia in Hausa-Fulani of North-Western Nigeria. Ethn Dis 2013;23:374-8.
Obirikorang, C, Osakunor DNM, Anto EO, Amponsah SO, Adarkwa OK. Obesity and cadiometabolic risk factors in urban and rural population in the Ashanti region-Ghana: A comparative cross sectional study. PLoS One 2015;10:e0129494.
Manning, JT, Scutt D, Wilson J, Lewis-Jones DI. The ratio of 2nd
digit length: A predictor of sperm numbers and concentrations of testosterone, leutinizing hormone and estrogen. Hum Repr 1998;13:3000-4.
Danborno B, Danborno AM. The effect of the season of birth and fluctuating asymmetry on second and fourth digit lengths and digit ratio (2D:4D) in Nigerians. Eur J Zool Res 2015;4:7-11.
Haffner SM, Ferrannini E, Hazuda HP, Stern MP. Clustering of cardiovascular risk factors in confirmed prehypertensive individuals. Hypertension 1992;20:38-45.
Kondo T, Zakany J, Innis J. Of fingers, toes and penises. Nature 1997;390:29.
Mortlock DP, Innis JW. Mutation of HoxA
13 in hand-foot-genital syndrome. Nature Genet 1997;15:179-80.
Mussig K, Staiger H, Machicao F, Thamer C, Machann J, Schick F, et al
. RARRES2, encoding the novel adipokine chemerin, is a genetic determinant of disproportionate regional body fat distribution: A comparative magnetic resonance imaging study. Metabolism 2009;258:519-24.
Pausova Z, Abrahamowicz M, Mahboubi A, Syme C, Leonard GT, Perron M, et al
. Functional variation in the androgen-receptor gene is associated with visceral adiposity and blood pressure in male adolescents. Hypertension 2010;55:706-14.
Tchernof A, Bélanger C, Morisset AS, Richard C, Mailloux J, Laberge P, et al
. Regional differences in adipose tissue metabolism in women: Minor effect of obesity and body fat distribution. Diabetes 2006;55:1353-60.
Zhao D, Li B, Yu K, Zheng L. Digit ratio (2D:4D) and hand grip strength in subjects of Han ethnicity: Impact of sex and age. Am J Phys Anthropol 2012;149:266-71.
Manning JT. The ratio of 2nd
digit length and performance in skiing. J Sports Med Phys Fit 2002;42:446-50.
[Table 1], [Table 2], [Table 3], [Table 4]