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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 71  |  Issue : 3  |  Page : 214-219

Relationship between digit ratio of 2D:4D and The physical health among college students of han ethnicity in Southern Fujian


1 Department of Basic Medicine and Department of Clinical Medicine, Zhangzhou Health Vocational College; Fujian Collaborative Innovation Center for Translation Medical Testing and Application Technology, Zhangzhou, Fujian Province, China
2 Department of Rehabilitation Medicine, Zhangzhou Municipal Hospital of Fujian Province, Zhangzhou, Fujian Province, China

Date of Submission19-Nov-2021
Date of Decision29-Jan-2022
Date of Acceptance21-Jun-2022
Date of Web Publication20-Sep-2022

Correspondence Address:
Prof. Tongjun Chen
Zhangzhou Health Vocational College, Zhangzhou, Fujian Province; Fujian Collaborative Innovation Center for Translation Medical Testing and Application Technology, Zhangzhou, Fujian Province
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jasi.jasi_189_21

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  Abstract 


Introduction: Studying the association between finger length ratios of 2D:4D and the physical health among college students of Han ethnicity in Southern Fujian can provide an indirect macrobiology reference index for early predictions of physical health status. Material and Methods: A total of 835 students in Southern Fujian were selected as test subjects through a stratified cluster sampling method. The 2D:4D ratio was recorded using physical measurement methods. The body mass index (BMI), vital capacity, 50-m run, and sit-and-reach test results were collected and analyzed based on the National Student's Health Standards. Results: Among male Han college students in Southern Fujian, the left 2D:4D ratio was negatively correlated with the vital capacity and sit-and-reach test results, while the right 2D:4D ratio was negatively correlated with the vital capacity, 50-m run, and sit-and-reach test results, as well as the comprehensive evaluation result of physical health. Among female Han college students in Southern Fujian, the left 2D:4D ratio was positively correlated with BMI and negatively correlated with the vital capacity, 50-m run, and 800-m run results, as well as the comprehensive evaluation result of physical health. The right 2D:4D ratio was negatively correlated with the vital capacity, 50-m run, 800-m run, and sit-and-reach test results, as well as the comprehensive evaluation results of physical health. The comprehensive evaluation results of physical health were statistically significant differences among low, medium, and high bilateral 2D:4D groups of female students, with poorer results in the high 2D:4D group than that of the medium and low 2D:4D groups. Discussion and Conclusion: The bilateral 2D:4D ratio of female and right 2D:4D ratio of male Han college students in Southern Fujian has a correlation with the comprehensive evaluation of physical health, which can serve as one of the reference indexes for adolescents' early health education, physical health monitoring, dietary intervention, and athlete selection.

Keywords: College students, digit ratio, Han ethnic group, Southern Fujian, the physical health


How to cite this article:
Chen T, Xiang J, Teng S, Huang Z, Li X, Huang L, Chen H, Luo B. Relationship between digit ratio of 2D:4D and The physical health among college students of han ethnicity in Southern Fujian. J Anat Soc India 2022;71:214-9

How to cite this URL:
Chen T, Xiang J, Teng S, Huang Z, Li X, Huang L, Chen H, Luo B. Relationship between digit ratio of 2D:4D and The physical health among college students of han ethnicity in Southern Fujian. J Anat Soc India [serial online] 2022 [cited 2022 Sep 29];71:214-9. Available from: https://www.jasi.org.in/text.asp?2022/71/3/214/356492




  Introduction Top


The Student's Physique and Health Standard was introduced in 2002 in China. After further exploration and a summary of experience, the National Student Physical Health Standard (Revised in 2014) (hereinafter referred to as “The Standard”) was issued by the Ministry of Education, to assess students' physical health from their body shape, function, and fitness. This lays a good foundation for providing reference standards on the development of students' physical health.

Digit ratio refers to the ratio of finger lengths. The length of the thumb to the little finger (1–5) is expressed as 1D-5D; however, it is generally difficult to determine the length of the thumb, so 2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D and 4D:5D are usually used, of which the second finger–to fourth finger length ratio (2D:4D) is most commonly used. Digit ratio is determined by the HOX gene[1] and is affected by intrauterine sex hormones during embryonic development,[2] with a positive correlation with maternal intrauterine testosterone and a negative correlation with estrogen. Human right-hand 2D:4D is negatively correlated with the testosterone/estradiol ratio in amniotic fluid.[3] Digit ratio remains unchanged during individual growth, so it can serve as a marker for perinatal sex hormone levels. In addition to digit ratio, body mass index (BMI), exercise skills, and exercise capacity are also associated with perinatal sex hormone levels.[4],[5],[6] Scholars found that prenatal sex hormone levels have a certain impact on the flexibility and muscle strength of adolescent females.[7] A lower 2D:4D often corresponds to a better physical ability and greater exercise performance.[8] especially in athletes involving in aerobic exercise[5] including rowing athletes,[9] elite tennis players,[10] and swimmers.[11] Perinatal sex hormone levels are also related to body size and the distribution of substances in the body.[12] Digit ratio (2D:4D) is associated with individual development and physical function[13],[14] but the relationship differs among ethnic groups in different regions.[15] Therefore, the relationship between digit ratio and physical health, assessed by BMI, cardiopulmonary function, and exercise capacity, deserves further attention and research. In the present study, the correlation between 2D:4D and physical health, and the possibility of an indirect macrobiological index for early prediction of physical health were explored among Han college students in Southern Fujian Province of China.


  Material and Methods Top


Material

Eight hundred and thirty-five participants (303 males and 532 females) aged 17–21-year-old were selected from undergraduate classes of 2018 and 2019 attending Zhangzhou Health Vocational College in Fujian Province. The participants were chosen through stratified random cluster sampling from September 2018 to January 2020. The inclusion criteria include: Han people in Southern Fujian (Zhangzhou, Xiamen and Quanzhou) within 3 generations; no major somatopsychic illness; no dyskinesia, no injured or deformed fingers, having never received special physical training, and with a mother that did not take any hormone drugs during pregnancy. This study was reviewed and approved by the Ethics Department of the college, and informed consent was obtained from all students.

Methods

According to the Anthropometric Manual authored by Shao XQ,[16] the finger length of subjects was measured through the indirect method, specifically as follows: The photos of both palms were taken using a digital camera at a fixed shooting distance. Then, the measuring point of each finger was marked using the image analysis software on a computer, and the photos were printed in color [Figure 1]. Finally, the straight-line distance between the midpoint of the palmar flexural fold of the proximal phalanx and the midpoint of the fingertip was measured using an electronic digimatic caliper (Guanglu Measuring Instrument Co., Ltd., China, 0–150 mm, precision: 0.01 mm).
Figure 1: The schematic diagram of each digit length

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A total of eight indexes were measured for each subject according to the requirements and regulations in The Standard,[17] including body shape indexes (height [cm] and weight [kg]), body function indexes (vital capacity [mL]), and body fitness indexes (speed fitness test: 50-m run [s], flexibility fitness test: Sit-and-reach (cm), lower limb explosive strength test: Standing broad jump [cm], strength fitness test: Chin-up for males [times] and 1 min crunches for females [times], endurance fitness test: 1000-m run for males [s] and 800-m run for females [s]). The vital capacity was measured in a standing position using a spirometer. Each subject repeated the test twice with an interval of 30 s. The sit-and-reach test was measured using a sit and reach box (brand, city). The subject sat with legs stretched and feet 10–15 cm apart on the test board. They were instructed to bend forward and push the cursor as far as they could. The test was repeated twice. The higher of the two was used in the analysis. The standing broad jump test measures the distance of the double leg jump in centimeters. The 1 min crunches test measures how many crunches the subject can do in a minute. The testing position was supine with foot on the plinth, hips and knees at 90°, and fingers crossed behind the head. A tester held the subject's ankle for fixation. A successful attempt is counted when the subject completing the sitting-up with the elbow touching the knees while keeping the hands behind or around the head. The 50-m run test and 1000-m (800-m) run test were measured in seconds using a stopwatch. Height and weight were measured and BMI was calculated as weight (kg)/height (m)2. The test results were assessed according to The Standard.

Quality control

Two testers received standardized training before the start of the study. Intrarater and interrater reliabilities were assessed using correlation coefficient and reached 0.94 or higher in all tests using in this study.

Statistical procedures

A database was set up using EpiData 3.1 (EpiData Association; Odense, Denmark) software. SPSS 22.0 (IBM Corp. Armonk, NY, USA) software was utilized for all statistical analyses. Descriptive analysis was expressed as mean ± standard deviation (χ ± s). Reliability and correlation were analyzed using Pearson correlation analysis and variance tests. ANOVA and post hoc analyses were used to compare the differences among the three groups. The significance level was set at α = 0.05.


  Results Top


Among Han male college students in Southern Fujian, the left 2D:4D was negatively correlated with vital capacity and sit-and-reach results, but had no correlations with other indexes. The right 2D:4D was negatively correlated with vital capacity, 50-m run, sit-and-reach results, and the total score of physical health, but had no correlations with other indexes [Table 1].
Table 1: The correlation analysis between finger length ratio of second finger–to fourth finger length ratio and the physical health related indexes of College Students of Han male ethnic in southern Fujian (r)

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Among Han female college students in Southern Fujian, the left 2D:4D was positively correlated with BMI, and negatively correlated with vital capacity, 50-m run, 800-m run, and the total score of physical health. The right 2D:4D was negatively correlated with vital capacity, 50-m run, 800-m run, sit-and-reach results, and the total score of physical health [Table 2].
Table 2: The correlation analysis between finger length ratio of second finger–to fourth finger length ratio and the physical health related indexes of College Students of Han female ethnic in southern Fujian (r)

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Using the 25th and 75th percentile of bilateral 2D:4D of Han college students in Southern Fujian as cutoff scores, all subjects were divided into low, mid, and high 2D:4D groups. It was found that the chin-up results had statistically significant differences among male right-hand low, mid, and high 2D:4D groups. The post hoc analysis revealed that the low 2D:4D group is significantly different from the mid and high 2D:4D groups [Table 3].
Table 3: Differences in physical health-related indexes in bilateral low, medium and high second finger–to fourth finger length ratio groups among College Students of Han male ethnic in southern Fujian (X̄±S)

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The BMI, vital capacity, 50-m run and 800-m run results, and the total score were statistically significant differences among female left-hand low, mid, and high 2D:4D groups. The post hoc analysis revealed that the high 2D:4D group is different from the mid and low 2D:4D groups. The 800-m run results had a statistically significant difference between mid and low 2D:4D groups. There were statistically significant differences in BMI, vital capacity, 50-m run, 800-m run, standing broad jump and sit-and-reach results, and the total score among female right-hand low, mid, and high 2D:4D groups. The vital capacity, 50-m run and sit-and-reach results and the total score all had statistically significant differences in the high 2D:4D group compared with those in the mid and low 2D:4D groups. Moreover, there was a statistically significant difference in BMI between high and low 2D:4D groups, and also in standing board jump results between high and mid 2D:4D groups [Table 4].
Table 4: Differences in physical health-related indexes in bilateral low, medium and high second finger–to fourth finger length ratio groups among College Students of Han female ethnic in southern Fujian (X̄±S)

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  Discussion Top


In October 2016, the 2030 Planning Outline of Healthy China was issued by the Central Committee of the Communist Party of China and the State Council of the PRC.[18] As stipulated in Section 4 of Chapter 6, adolescents are listed as the target population for the implementation of the physical health plan, and it is also required that the interest of adolescents in physical exercise be developed through the implementation of the youth sports promotion program, with an excellence rate of more than 25% in The Standard as a quantifiable goal. China has decided to enhance the physical health of students as an approach to achieve the goal of healthy China. The Standard comprehensively assesses the students' physical health from body shape, function, and fitness. Body shape indexes are an important basis reflecting the growth and development speed and nutritional status of the human body.[19] BMI displays the relation between adults' weight and height, which is recommended by the WHO as a preferred index for assessing overweight and obesity and their change trends and can also be used to measure the fat distribution in the human body.[20]

In the present study, the BMI was significantly higher among female students in the left-hand high 2D:4D group than that of the mid and low 2D:4D groups, and it was also significantly higher in the right-hand high 2D:4D group than that of the low 2D:4D group. Fink et al.[21] found that BMI positively correlates with left hand 2D:4D in males. In females, the reversed relationship was found but it was not statistically significant. Muller et al.[22] found that 2D:4D is not strongly associated with adult anthropometric measures. BMI is greatly affected by gender, ethnicity, living habits, age, and regional dietary rules. Therefore, the correlation results between 2D:4D and BMI in different regions, ethnicities, and genders are not consistent. It is well known that BMI reflects the overall body fat content, whereas the waist circumference and waist-to-hip ratio reflect the abdominal fat content. All three can reflect body fat content, but each has certain limitations. If an index, such as the 2D:4D can be used to represent all three measures then it can provide a useful alternative for estimating body composition.

Body function refers to the functional capability of organs and systems in the body. Vital capacity, i.e., maximum lung capacity in one-time ventilation, is an important index for assessing respiratory function. In this study, both male and female bilateral 2D:4D had a negative correlation with vital capacity, and vital capacity in the female bilateral high 2D:4D group was significantly lower than that of the mid and low 2D:4D groups. However, vital capacity was measured in a one-time ventilation test and closely related to height and weight, thus failing to fully reflect the elastic state of lung tissues and the patency degree of the airway,[23] so it had certain limitations. Therefore, vital capacity/weight ratio will be considered for future analysis, to display the differences in body function and physical activity more objectively and analyze their correlations with digit ratio (2D:4D) more scientifically and reasonably.

Body fitness is a general term for the speed, strength, endurance, and flexibility of the human body in muscle activities. Scholars in China also found the correlation between 2D:4D and human body fitness in research on the digit ratio of university students in Jinzhou and Guangdong youthsm,[24],[25] but the results are not consistent. In the present study, it was found that male bilateral 2D:4D was negatively correlated with the sit-and-reach results among Han college students in southern Fujian, indicating that males with lower right 2D:4D had better performance in the 50-m run. This result is consistent with the result from Manning and Hill on 241 boys.[5] Right 2D:4D had no correlation with the chin-up results, but the low 2D:4D group performed worse than those in the mid and high 2D:4D groups. Besides, this study found that females with higher right 2D:4D have poorer body flexibility. In addition, females with a lower bilateral 2D:4D finger length ratio had better endurance and speed. The result is consistent with those of Pasanen et al.[26] He studied the correlation between 2D:4D and sports performance of 114 boys and 175 girls and found that their sports performance was negatively correlated with the female bilateral 2D:4D and male right 2D:4D. However, the result differs from the result from Lombardo et al.[27] in which digit ratio and physical skills and fitness were negatively correlated on the right side of male, but not in female. We speculate that the difference may be due to the elite status of young athletes and the small sample size in the study by Lombardo et al. Whether the strength test results are associated with 2D:4D remains to be further analyzed after collecting more data from different types of strength tests in the future.

Through the comprehensive assessment of physical health based on The Standard, it was found that the higher female bilateral 2D:4D and male right 2D:4D indicated a lower total score of physical health, and the total score was significantly lower in the female high 2D:4D group than that of the mid and low 2D:4D groups. Experiments with rodents show that the length of 2D is positively influenced by prenatal exposure to estrogen, whereas the length of 4D is positively influenced by prenatal testosterone exposure.[28],[29],[30] In humans, 2D:4D is established by the end of the first trimester.[31] Prenatal testosterone exposure may also affect subsequent athletic behavior and performance.[32],[33],[34] Athletic prowess in both males and females, especially their performance on distance running,[35],[36],[37] is associated with smaller 2D:4D.[38],[39] The relationship between 2D:4D and athletic prowess may be mediated by the effects of prenatal testosterone exposure on the cardiovascular system.[39] Multiple lines of evidence suggest that prenatal testosterone exposure influences not only sports performance but also sports interest and motivation.[34],[40] It can be speculated that higher levels of androgen in individuals and mothers during embryonic development have a greater impact on the body function and fitness of females and males.


  Conclusion Top


It was found that female bilateral 2D:4D and male right 2D:4D can serve as one of the macrobiological indexes indirectly predicting the physical health of college students, which offers a basis for early health education, physical health monitoring, lifestyle (diet) intervention, and athlete selection among adolescents. Body fitness is comprehensively assessed using a variety of parameters and affected by genetics, nutritional status and lifestyle. In this study, young Han college students in Southern Fujian were used as the subjects, thus reducing the errors caused by living environment, habits, human body development, and hormone levels in vivo to a certain extent. Other influencing factors, however, were not collected and analyzed, so further research is needed in future.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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