Weight Control Behaviors, Health-related Quality of Life and Nutritional Status by Overestimation of Body Image among Young Korean Females: Data from the Fifth Korea National Health and Nutrition Examination Survey, 2010–2011

Article information

Korean J Community Nutr. 2015;20(5):362-374

Publication date (electronic) : 2015 January 20

doi : https://doi.org/10.5720/kjcn.2015.20.5.362

Seulki Park ¹⁾, Taisun Hyun ²⁾, Hongmie Lee ¹⁾^,

¹⁾Department of Food Science & Nutrition, Daejin University, Pochoeon, Keonggi, Korea

²⁾Department of Food and Nutrition, Chungbuk National University, Cheongju, Chungbuk, Korea

^†Corresponding author Hongmie Lee Department of Food Science & Nutrition, Daejin University, 1007, Hoguk-ro, Pocheon-si, Gyeonggi 11159, Korea Tel: (031) 539-1862 Fax: (031) 539-1860 E-mail: hmlee@daejin.ac.kr

Received 2015 August 20; Revised 2015 September 22; Accepted 2015 October 13.

Abstract

Objectives

This study was performed to investigate the effects of overestimation of their own body shape on weight control behaviors, mental condition, physical activity, dietary behavior, health-related quality of life, and nutritional status among young Korean females. Methods: A total of 1,514 women aged 20–39 years who are not pregnant and lactating among those who participated in the Fifth Korea National Health and Nutrition Examination Survey (2010∼2011), were analyzed and grouped into underestimation (n=120), normal estimation (NE, n=840), and overestimation (OE, n=554), based on their body perception compared to actual percent ideal body weights. Variables were compared between OE group and NE group. Results: The subjects in OE group were significantly younger (29.5 vs. 30.5 years, respectively p < 0.05) and had lower body mass index (20.9 vs. 22.2 respectively, p < 0.01), health-related quality of life measured by EQ-5D (EuroQol-5 Dimension)(0.97 vs. 0.98 respectively, p < 0.05), nutrition adequacy ratio (NAR) of protein (0.91 vs. 0.93 respectively, p < 0.05), phosphorous (0.93 vs. 0.96 respectively, p < 0.05), and iron (0.70 vs. 0.75 respectively, p<0.01), and index of nutrition quality (INQ) of iron (0.84 vs. 0.89 respectively, p < 0.05) compared to those in the NE group. The results of logistic regression showed that unmarried status (OR 1.32; 1.01∼1.72) and severely underweight/underweight status (OR 1.94; 1.01∼3.75)/(OR 1.81; 1.34∼2.45) were significantly related to the probability of overestimation by the subjects. Significantly more women in OE group practiced fasting, skipping meals, and taking prescribed pills to lose body weights and had skipped breakfast compared to those in the NE group. Conclusions: The results of this study suggested that the Korean young women's distorted perception of own body shape may be associated with undesirable weight control behavior, low quality of life, and lower nutritional status. Therefore, nutrition education for this group should include information on correct body shape perception and its importance.

Keywords: weight perception; health-related quality of life; nutrition intake

Table 1.

The distribution of the study participants according to weight status and subjective weight perception

Table 2.

The distribution of the study participants according to weight perception and weight status

Table 3.

General characteristics of the study participants by weight perception

Table 4.

Odds ratios for prevalence of overestimation according to general characteristics of the study participants

Table 5.

Experience and methods of weight control by weight perception

Table 6.

Mental condition and quality of life by weight perception

Table 7.

Dietary habits by weight perception

Table 8.

Daily nutrients intakes and macronutrients energy ratio by weight perception

Table 9.

NAR and MAR by weight perception

Table 10.

Index of nutrition quality by weight perception

References

1. World Health Organization. Obesity: preventing and managing the global epidemic report of a WHO consultation (WHO Technical Report Series 894) [internet] WHO; 1998. [cited 2015 Aug 13]. Available from: http://www.who.int/nutrition/publications/obesity/WHO_TRS_894/en/.

2. Korea Centers for Disease Control and Prevention·Ministry of Health and Welfare. Korea health statistics 2013: The Sixth Korea National Health and Nutrition Examination Survey (KNHANES VI-1) [internet]. 2014. [cited 2015 Aug 13]. Available from: https://knhanes.cdc.go.kr/knhanes/index.do.

3. Ryu HK. A survey of adolescents' concern and perception about body image. Korean J Community Nutr 1997;2(2):197–205.

4. Hong MS, Pak HO, Sohn CY. A study on food behaviors and nutrient intakes according to body mass index and body image recognition in female university students from Incheon. Korean J Food Nutr 2011;24(3):386–395.

5. Chang HS. A study on weight control behaviour, eating habits and health-related life habits according to obesity degree by body fat percentage among middle-aged women in Gunsan city. Korean J Community Nutr 2010;15(2):227–239.

6. Lim YS, Park NR, Jeon SB, Jeong SY, Tserendejid Z, Park HR. Analysis of weight control behaviors by body image perception among Korean women in different age groups: Using the 2010 Korea national health and nutrition examination survey data. Korean J Community Nutr 2015;20(2):141–150.

7. Kim HJ, Jang HS. Comparison between body perception, attitude on weight-control and self-esteem according to the weight group of high school students in Daegu. J Korean Home Econ Educ Assoc 2009;21(2):1–22.

8. Cho JH, Han SN, Kim JH, Lee HM. Body image distortion in fifth and sixth grade students may lead to stress, depression, and undesirable dieting behavior. Nutr Res Pract 2012;6(2):175–181.

9. Kim MS, Lee HM. Overestimation of own body weights in female university students: associations with lifestyles, weight control behaviors and depression. Nutr Res Pract 2010;4(6):499–506.

10. Cuypers K, Kvaloy K, Bratberg G, Midthjell K, Holmen J, Holmen TL. Being normal weight but feeling overweight in adolescence may affect weight development into young adulthood-an 11-year followup: The HUNT study, Norway. J Obes 2012;601872:1–8.

11. Stice E, Bearman SK. Body-image and eating disturbances prospectively predict increases in depressive symptoms in adolescent girls: A growth curve analysis. Develop Psychol 2001;37(5):597–607.

12. Oh JY, Park KH. The effect of overvaluation of shape and weight on binge eating. Korean J Health Psychol 2011;16(4):739–757.

13. Cho HS, Choi MK. A study on body image and dietary habits by the body mass index of middle school students in Chungnam. Korean J Food Nutr 2010;23(3):368–375.

14. Ehrenberg HM, Dierker L, Milluzzi C, Mercer BM. Low maternal weight, failure to thrive in pregnancy, and adverse pregnancy outcomes. Am J Obstet Gynecol 2003;189(6):1726–1730.

15. Yu Z, Han S, Zhu J, Sun X, Ji C, Guo X. Prepregnancy body mass index in relation to infant birth weight and offspring overweight/obesity: a systematic review and metaanalysis. PLoS ONE 2013;8(4):e61627.

16. Seo JS, Lee JH, Yoon JS, Cho SH, Choi YS. Nutritional Assessment 1st ed.th ed. Seoul: Powerbook; 2008. p. 150–153.

17. Kim MH, Cho YS, Uhm WS, Kim S, Bae SC. Cross-cultural adaptation and validation of the Korean version of the EQ-5D in patients with rheumatic diseases. Qual Life Res 2005;14(5):1401–1406.

18. The Korean Nutrition Society. Dietary reference intakes for Koreans. 1st revision Seoul: The Korean Nutrition Society; 2010. p. 25–46.

19. Park SK. A survey on weight control, mental condition, physical activity, dietary behavior, and nutritional status by body perception in Korean female [Master's thesis]. Daejin University; 2014.

20. Min JS. A study on physical condition, body image perception, eating disorder risk, and depression level according to diet experience of some female high school students in Seoul [Master's thesis]. Daejin University; 2015.

21. Klos LA, Sobal J. Marital status and body weight, weight perception, and weight management among US adults. Eat Behav 2013;14(4):500–507.

22. Montani JP, Schutz Y, Dulloo AG. Dieting and weight cycling as risk factors for cardiometabolic diseases: who is really at risk? Obes Rev 2015;16(Suppl 1):7–18.

23. Yoon SH, Han KT, Kim SJ, Sohn TY, Jeon B, Kim W, et al. Combined effect of body mass index and body size perception on metabolic syndrome in South Korea: results of the fifth Korea National Health and Nutrition Examination Surveys (2010–2012). BMC Public Health 2015;15(1):1–15.

24. Tang J, Yu Y, Du Y, Ma Y, Zhu H, Liu Z. Association between actual weight status, perceived weight and depressive, anxious symptoms in Chinese adolescents: a cross-sectional study. BMC Public Health 2010;10(1):1–8.

25. Jansen W, van de Looij-Jansen PM, de Wilde EJ, Brug J. Feeling fat rather than being fat may be associated with psychological wellbeing in young Dutch adolescents. J Adolesc Health 2008;42(2):128–136.

26. Farhat T, Iannotti RJ, Summersett-Ringgold F. Weight, weight perceptions, and health-related quality of life among a national sample of US girls. J Dev Behav Pediatr 2015;36(5):313–323.

27. Chung JY, Lee MY, Kim MJ. A study on the prevalence of chronic diseases, health-related habits and nutrients intakes according to the quality of life in Korean adults. Korean J Community Nutr 2010;15(4):445–459.

28. Lee HS. The factors influencing health-related quality of life in the elderly – Focused on the general characteristics, health habits, mental health, chronic diseases, and nutrient intake status: data from the fifth Korea National Health and Nutrition Examination Survey (KNHANES V), 2010–2012. Korean J Community Nutr 2014;19(5):479–489.

29. Kim KW, Shin EM. A study on nutrition knowledge, nutritional attitudes, dietary behavior and dietary intake by weight control attempt among middle school female students. Korean J Community Nutr 2002;7(1):23–31.

30. Sung SJ, Kwon SJ. Effect of eating with family or alone on the self-rated mental or physical health: The elementary school children in Daejeon area. Korean J Community Nutr 2010;15(2):206–226.

31. Cason KL. Family mealtimes: more than just eating together. J Am Diet Assoc 2006;106(4):532–533.

Article information Continued

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Table 1.

The distribution of the study participants according to weight status and subjective weight perception

Subjective weight perception	Weight status
Subjective weight perception	Severe under weight	Under weight	Normal weight	Over weight	Obese	Total
Very thin	24 (42.9)^1)a2)	10 (4.5)^c	−	−	−	34 (662.7)
Somewhat thin	27 (50.0)^b	119 (42.6)^a	21 (2.4)^c	−	−	167 (611.9)
Normal	3 (7.1)^b	164 (52.0)^b)	450 (57.9)^a	13 (8.2)^c	3 (2.0)^c	633 (641.2)
Somewhat fat	−	2 (0.9)^b	315 (38.0)^b	133 (71.9)^a	73 (35.7)^c	523 (632.7)
Very fat	−	−	13 (1.7)^b	30 (19.9)^b	114 (62.3)^a	157 (611.5)
Total	54 (64.2)	295 (20.3)	799 (50.2)	176 (12.1)	190 (13.2)	1,514 (100.0)

¹⁾

N (%) 2) a: 840 (56.4%) of total 1,514 estimated own weight status normally, b: 554 (35.5%) of total 1,514 overestimated own weight, c: 120 (8.1%) of total 1,514 underestimated own weight, all of whom were not included for further analysis

Table 2.

The distribution of the study participants according to weight perception and weight status

Actual weight status	Weight perception
Actual weight status	Under estimation	Normal estimation	Over estimation	Total
Severe underweight	−	24 (13.2)	30 (16.8)	54 (114.2)
Underweight	110 (11.3)¹⁾	119 (15.3)	166 (30.3)	295 (120.3)
Normal weight	121 (14.8)	450 (51.5)	328 (56.1)	799 (150.2)
Overweight	113 (12.4)	133 (15.5)	30 (16.8)	176 (112.1)
Obese	176 (61.5)	114 (14.5)	−	190 (113.2)
Total	120 (18.1)	840 (56.4)	554 (35.5)	1,514 (100.0)

¹⁾

N (%)

Table 3.

General characteristics of the study participants by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over estimation	Total
	(n=840)	(n=554)	(n=1,394)
Age (year)	130.5± 0.25¹⁾	129.5± 0.33	130.1± 0.21	< 0.019∗
Height (cm)	160.6± 0.22	161.0± 0.29	160.7± 0.18	< 0.252
Weight (kg)	157.3± 0.51	154.2± 0.35	156.1± 0.35	< 0.001∗∗∗
PIBW²⁾ (%)	103.0± 0.87	196.9± 0.58	100.6± 0.59	< 0.001∗∗∗
BMI³⁾ (kg/m²)	122.2± 0.19	120.9± 0.12	121.7± 0.13	< 0.001∗∗∗

¹⁾

Mean± SE 2) Percent ideal body weight 3) Body mass index ∗: p < 0.05, ∗∗∗: p < 0.001 by Student's t test.

Table 4.

Odds ratios for prevalence of overestimation according to general characteristics of the study participants

General characteristics		N (%)	OR (95% CI)¹⁾
Age group	30∼39	355 (50.6)	1.00
Age group	20∼29	199 (49.4)	1.13 (0.88∼1.45)
Marital status	Married	351 (52.6)	1.00
Marital status	Unmarried	203 (47.4)	1.32 (1.01∼1.72)
Region	Urban area	500 (91.0)	1.00
Region	Rural area	54 (69.0)	1.48 (0.94∼2.32)
Income level	Low	119 (35.6)	1.00
	Mid-low	149 (26.2)	1.27 (0.88∼1.83)
	Mid-high	139 (25.4)	1.14 (0.81∼1.59)
	High	147 (22.8)	1.21 (0.83∼1.77)
Educational level	Elementary school	2 (60.4)	1.00
	Middle school	7 (62.1)	2.48 (0.32∼19.12)
	High school	211 (39.1)	1.40 (0.24∼8.10)
	College	334 (58.4)	1.73 (0.30∼9.90)
Body shape	Normal weight	328 (56.1)	1.00
	Severe underweight	30 (66.8)	1.94 (1.01∼3.75)
	Underweight	166 (30.3)	1.81 (1.34∼2.45)
	Overweight	30 (66.8)	0.40 (0.25∼0.66)
Occupation	Unemployed	290 (48.1)	1.00
	Administrator	110 (20.5)	0.98 (0.70∼1.39)
	Office job	65 (13.1)	0.79 (0.53∼1.18)
	Sales and service	65 (12.9)	0.99 (0.67∼1.49)
	Labor	24 (65.4)	0.83 (0.42∼1.66)

¹⁾

Odds ratio (95% confidence interval)

Table 5.

Experience and methods of weight control by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over estimation	Total
	(n=840)	(n=554)	(n=1,394)
Weight control to lose or maintain
Yes	557 (68.2)¹⁾	386 (67.7)	963 (68.0)	0.859
No	263 (31.8)	168 (32.3)	431 (32.0)	0.859
Method used for weight control
Exercise
Yes	354 (61.9)	227 (56.7)	581 (59.9)	0.176
No	223 (38.1)	159 (43.3)	382 (40.1)	0.176
Fasting
Yes	5 (60.5)	12 (63.3)	17 (61.6)	0.001∗∗
No	572 (99.5)	374 (96.7)	946 (98.4)	0.001∗∗
Reducing food intakes
Yes	394 (67.8)	278 (68.5)	672 (68.1)	0.848
No	183 (32.2)	108 (31.5)	291 (31.9)	0.848
Skipping meals
Yes	70 (13.8)	67 (20.1)	137 (16.2)	0.048∗
No	507 (86.2)	319 (79.8)	826 (83.8)	0.048∗
Un-prescribed pills
Yes	2 (60.4)	6 (61.7)	8 (60.9)	0.099
No	575 (99.6)	380 (98.3)	955 (99.1)	0.099
Prescribed pills
Yes	29 (65.4)	33 (10.4)	62 (67.4)	0.039∗
No	548 (94.6)	353 (89.6)	901 (92.6)	0.039∗
Herbal medicine
Yes	19 (63.0)	18 (65.8)	37 (64.1)	0.066
No	558 (97.0)	368 (94.2)	926 (95.9)	0.066
Health functional food
Yes	31 (64.8)	31 (67.5)	62 (65.8)	0.142
No	546 (95.2)	355 (92.5)	901 (94.2)	0.142
One-food diet
Yes	14 (62.2)	8 (62.2)	22 (62.2)	0.961
No	563 (97.8)	378 (97.8)	941 (97.8)	0.961

¹⁾

N (%) ∗: p < 0.05, ∗∗: p < 0.01 by χ

test

Table 6.

Mental condition and quality of life by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over estimation	Total
	(n=840)	(n=554)	(n=1,394)
Feeling stress
Much	282 (36.7)¹⁾	198 (40.1)	480 (38.0)	0.313
A little	558 (63.3)	356 (59.9)	914 (62.0)	0.313
Feel depressed
Yes	102 (14.5)	78 (15.1)	180 (14.7)	0.795
No	738 (85.6)	476 (84.9)	1,214 (85.3)	0.795
Thinking of suicide
Yes	113 (15.1)	96 (19.6)	209 (16.9)	0.115
No	727 (84.9)	458 (80.4)	1,185 (83.1)	0.115
Counseling at a mental clinic
Yes	2 (63.6)	12 (62.1)	34 (63.1)	0.206
No	818 (96.4)	542 (97.9)	1,360 (96.9)	0.206
EQ-5D²⁾	0.98± 0.00³⁾	0.97± 0.00	0.97± 0.00	0.025∗
EQ-VAS⁴⁾	74.7± 0.55	73.5± 0.71	74.2± 0.43	0.177

¹⁾

N (%) 2) Euro Quality of Life – 5 Dimension 3) Mean± SE 4) Euro Quality – visual analog scale ∗: P < 0.05 by Student's t-test

Table 7.

Dietary habits by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over estimation	Total
	(n=840)	(n=554)	(n=1,394)
Skip breakfast
Yes	279 (38.4)¹⁾	222 (46.8)	501 (41.6)	0.008∗∗
No	561 (61.6)	332 (53.2)	893 (58.4)	0.008∗∗
Skip lunch
Yes	85 (12.5)	68 (14.1)	153 (13.1)	0.517
No	755 (87.5)	486 (85.9)	1,241 (86.9)	0.517
Skip dinner
Yes	71 (69.7)	45 (68.7)	116 (69.3)	0.566
No	769 (90.3)	509 (91.3)	1,278 (90.7)	0.566
Have breakfast with family
Yes	392 (52.7)	295 (60.9)	687 (55.9)	0.011∗
No	448 (47.3)	259 (39.1)	707 (44.1)	0.011∗
Have lunch with family
Yes	173 (20.4)	110 (18.9)	283 (19.8)	0.532
No	667 (79.6)	444 (81.1)	1,111 (80.2)	0.532
Have dinner with family
Yes	619 (67.9)	408 (67.0)	1,027 (67.6)	0.741
No	221 (32.1)	146 (33.0)	367 (32.4)	0.741
Know about nutrition labels
Yes	794 (93.8)	521 (93.1)	1,315 (93.5)	0.705
No	46 (66.2)	33 (66.9)	79 (66.5)	0.705
Use nutrition labels when food is consumed
Yes	407 (51.3)	283 (52.9)	690 (51.9)	0.626
No	386 (48.7)	238 (47.1)	624 (48.1)	0.626
Eating out (times/week)	3.53± 0.29²⁾	3.44± 0.13	3.49± 0.10	0.574

¹⁾

N (%) 2) Mean± SE ∗: p < 0.05, ∗∗: p < 0.01 by χ

test

Table 8.

Daily nutrients intakes and macronutrients energy ratio by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over estimation	Total
	(n=840)	(n=554)	(n=1,394)
Energy (kcal)	1,813.02± 232.6¹⁾2	1,736.02± 240.1	1,722.02± 225.3	0.160
Protein (g)	68.72± 222.1	65.02± 222.1	64.82± 221.4	0.249
Fat (g)	44.82± 221.4	45.02± 221.6	42.52± 221.1	0.921
Carbohydrates (g)	280.02± 224.3	264.02± 225.8	267.02± 223.6	0.024∗
Dietary fiber (g)	6.12± 220.2	5.92± 220.3	6.02± 221.2	0.676
Calcium (mg)	449.02± 211.3	445.02± 214.9	446.02± 228.8	0.810
Phosphorous (mg)	1,054.02± 219.8	1,022.02± 227.7	1,020.02± 216.0	0.372
Iron (mg)	12.62± 220.3	11.82± 220.5	12.12± 220.3	0.170
Sodium (mg)	4,384.02± 114.0	4,289.02± 154.0	4,233.02± 295.3	0.634
Potassium (mg)	2,680.02± 253.7	2,589.02± 274.9	2,619.02± 244.6	0.342
Vitamin A (μgRE)	719.02± 225.6	688.02± 240.3	697.02± 223.7	0.513
Carotene (μg)	3,455.02± 132.0	3,407.02± 219.0	3,409.02± 130.0	0.842
Retinol (μg)	118.02± 227.3	108.02± 226.3	114.02± 225.3	0.283
Vitamin B₁ (mg)	1.23± 220.03	1.20± 220.03	1.18± 220.03	0.867
Vitamin B₂ (mg)	1.16± 220.03	1.14± 220.03	1.15± 220.02	0.149
Niacin (mg)	15.52± 220.4	15.62± 220.5	15.12± 220.3	0.949
Vitamin C (mg)	99.32± 223.9	98.62± 224.1	99.82± 223.2	0.900
Macronutrients energy ratio (%)
Carbohydrates	63.32± 220.5	62.12± 220.6	63.22± 220.4	0.172
Protein	15.12± 220.2	14.72± 220.2	14.92± 220.2	0.283
Fat	21.32± 220.4	22.42± 220.5	21.52± 220.3	0.061

¹⁾

Mean± SE adjusted for age, weight, BMI, marital status, and weight status ∗: P < 0.05 by Student's t-test

Table 9.

NAR and MAR by weight perception

Variables	Weight perception			P-value
	Normal estimation	Over- estimation	Total
	(n=840)	(n=554)	(n=1,394)
NAR¹⁾
Protein	0.93± 0.01²⁾	0.91± 0.01	0.92± 0.01	0.026∗
Calcium	0.63± 0.01	0.61± 0.02	0.61± 0.02	0.365
Phosphorous	0.96± 0.01	0.93± 0.01	0.95± 0.01	0.036∗
Iron	0.75± 0.01	0.70± 0.02	0.73± 0.01	0.007∗∗
Vitamin A	0.74± 0.02	0.71± 0.02	0.73± 0.01	0.181
Vitamin B₁	0.85± 0.01	0.82± 0.01	0.84± 0.01	0.122
Vitamin B₂	0.82± 0.01	0.78± 0.01	0.80± 0.01	0.608
Niacin	0.85± 0.01	0.83± 0.01	0.84± 0.01	0.102
Vitamin C	0.99± 0.04	0.99± 0.04	1.00± 0.03	0.900
MAR³⁾	0.84± 0.01	0.81± 0.01	0.83± 0.01	0.095

¹⁾

Nutrient adequacy ratio 2) Mean± SE adjusted for age, weight, BMI, marital status and weight status 3) Mean nutrient adequacy ratio ∗: p < 0.05, ∗∗: p < 0.01 by Student's t-test

Table 10.

Index of nutrition quality by weight perception

Variables	Weight perception			P-value
	Normal perception	Over perception	Total
	(n=840)	(n=554)	(n=1,394)
Protein	1.13± 0.01¹⁾	1.14± 0.02	1.14± 0.01	0.936
Calcium	0.73± 0.01	0.74± 0.02	0.74± 0.01	0.965
Phosphorous	1.18± 0.12	1.18± 0.12	1.18± 0.01	0.863
Iron	0.89± 0.02	0.84± 0.02	0.88± 0.01	0.014∗
Vitamin A	0.89± 0.02	0.87± 0.02	0.89± 0.02	0.544
Vitamin B₁	1.01± 0.01	1.00± 0.02	1.00± 0.01	0.847
Vitamin B₂	0.96± 0.02	0.95± 0.01	0.96± 0.01	0.469
Niacin	1.02± 0.03	1.01± 0.01	1.02± 0.01	0.609
Vitamin C	1.15± 0.04	1.14± 0.04	1.15± 0.03	0.926

¹⁾

Mean± SE adjusted for age, weight, body mass index, marital status, and weight status ∗: P < 0.05 by Student's t-test