Short Communication

International Journal of Obesity (2006) 30, 1163–1165. doi:10.1038/sj.ijo.0803248; published online 31 January 2006

Japanese men have larger areas of visceral adipose tissue than Caucasian men in the same levels of waist circumference in a population-based study

T Kadowaki1,2, A Sekikawa2, K Murata3, H Maegawa4, T Takamiya2, T Okamura1, A El-Saed2, N Miyamatsu5, D Edmundowicz6, Y Kita1, K Sutton-Tyrrell2, L H Kuller2 and H Ueshima1

  1. 1Department of Health Science, Shiga University of Medical Science, Shiga, Japan
  2. 2Graduate School of Public Health, University of Pittsburgh, PA, USA
  3. 3Department of Radiology, Shiga University of Medical Science, Shiga, Japan
  4. 4Department of Medicine, Shiga University of Medical Science, Shiga, Japan
  5. 5Department of Clinical Nursing, Shiga University of Medical Science, Shiga, Japan
  6. 6University of Pittsburgh Medical Center, PA, USA

Correspondence: Dr T Kadowaki, Department of Health Science, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan. E-mail: kadowaki@belle.shiga-med.ac.jp

Received 28 February 2005; Revised 21 November 2005; Accepted 29 December 2005; Published online 31 January 2006.

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Abstract

Visceral adipose tissue (VAT) is an independent risk factor for metabolic and cardiovascular disorders. There has been no study that demonstrated different abdominal fat distribution between Asian and Caucasian men. As the Japanese are less obese but more susceptible to metabolic disorders than Caucasians, they may have larger VAT than Caucasians at similar levels of obesity. We compared the abdominal fat distribution of the Japanese (n=239) and Caucasian-American (n=177) men aged 40–49 years in groups stratified by waist circumference in a population-based sample. We obtained computed tomography images and determined areas of VAT and subcutaneous adipose tissue (SAT). We calculated VAT to SAT ratio (VSR). The Japanese men had a larger VAT and VSR in each stratum, despite substantially less obesity overall. In multiethnic studies, difference in abdominal fat distribution should be considered in exploring factors related to obesity.

Keywords:

abdominal adipose tissue, visceral adipose tissue, Japanese, Caucasian

Visceral adipose tissue (VAT) is an independent risk factor for coronary heart disease (CHD),1 hypertension,2 type-2 diabetes,3 and impaired glucose tolerance (IGT).4 Accumulation of VAT is a form of obesity related to environmental factors such as diet and physical inactivity.5 As the Japanese are less obese but more susceptible to metabolic disorders than Caucasians,5 they may have larger VAT than Caucasians at similar levels of obesity. There have been reports of racial differences in abdominal fat distribution between Caucasians and Africans,6 Hispanics,7 and Asians.8, 9 Previous studies have shown that Asian-American and Caucasian men had no significant difference in VAT among volunteer participants.8 Likewise, a meta-analysis showed no significant difference in VAT between Japanese and Caucasian men.9 In these studies, VAT was compared after adjusting for other factors such as age and obesity. There has been no report directly comparing VAT between the Japanese and Caucasian men in a population-based sample. Therefore, we compared the abdominal fat distribution of the Japanese and Caucasian-American men aged 40–49 years in groups stratified by waist circumference in a population-based sample.

We recruited 240 American men aged 40–49 years (Caucasians: 82%), randomly selected from Allegheny County, Pennsylvania, US, and 240 Japanese men aged 40–49 years, randomly selected from Kusatsu, Shiga, Japan. We confined our analyses to Caucasian and Japanese men, because African men have been compared with Caucasians elsewhere,6 and we had only one man who categorized himself as neither Caucasian nor African-American. In order to compare the abdominal adipose tissue (AAT) distribution at similar levels of waist circumference, participants with extremely large or small waist circumference (beyond the levels of mean plusminus2 (s.d.)) were excluded from the present analysis. After excluding 44 non-Caucasian-Americans and 20 outliers in waist circumference, 416 (239 Japanese and 177 Caucasian) men were examined. Waist circumference was measured twice at the umbilical level at the end of the exhalation phase while the participant was standing upright, and the mean of the two measurements was calculated. Areas of the whole AAT and VAT were determined at the level between the fourth and fifth lumbar vertebrae, using computed tomography images obtained with the same apparatus at each site (GE-Imatron C150). Areas of subcutaneous adipose tissue (SAT) were calculated as AAT minus VAT, and VAT to SAT ratio (VSR) was calculated as VAT/SAT. The technician was blinded to the race/ethnicity and other identifiable information about the participants The intraclass correlation coefficients at our reading center are 0.99 for SAT and 0.99 for VAT. Written informed consent was obtained from each participant. The study protocol was reviewed and approved by the Institutional Review Boards of University of Pittsburgh, US, and Shiga University of Medical Science, Japan.

We stratified the participants into quartile strata (from the lowest Q1 to the highest Q4) by waist circumference. We compared the means of continuous variables using t-tests, and considered the difference significant at P-value<0.05 in two-tailed tests. We performed statistical analyses using a Statistical Package for the Social Sciences (SPSS Japan Inc. version 11.0 J, Tokyo, Japan).

Table 1 shows AAT, SAT, VAT, and VSR in each waist stratum and overall. Pearson's correlation coefficients between waist circumference and AAT were 0.90 for the Caucasian men and 0.92 for the Japanese men. The Japanese men had a significantly larger VSR than the Caucasian men in all waist circumference strata. The Japanese men had a significantly larger VAT than the Caucasian men in Q2 and Q3. In Q1 and Q4, the Japanese men had a larger VAT, although this difference was not statistically significant. The Japanese men had a larger VAT in each stratum, despite significantly smaller waist circumference, AAT, SAT, and VAT than the Caucasian men overall. In the waist circumference stratification, a higher proportion of the Japanese men was in the lower quartiles (Q1 and Q2), whereas a higher proportion of the Caucasian men was in higher quartiles (Q3 and Q4).


In this study, we demonstrated that the Japanese men had larger VAT and VSR than the Caucasian men in every waist circumference stratum. To our knowledge, this is the first report to compare the distribution of abdominal adipose tissue between Japanese and Caucasian men directly in a standardized manner.

These findings of greater VAT in Japanese men may help explain the greater incidence of type 2 diabetes in this population compared to Caucasian men.5, 10 As the Japanese have a larger VAT even at lower levels of obesity, it leads to a higher risk than Caucasians, because VAT is an independent predictor of type 2 diabetes3 and IGT.4 In fact, in the Diabetes Prevention Program, the obesity inclusion criterion was lower for Asians (BMIgreater than or equal to22 kg/m2) than other races (BMIgreater than or equal to24 kg/m2),11 based on the notion that the Japanese have higher risk of type 2 diabetes at lower levels of obesity.10

The reason we failed to demonstrate significant VAT differences in Q1 and Q4 may be due to insufficient sample sizes caused by the fact that waist circumference distribution was skewed to opposite directions in the two groups, resulting in a smaller proportion of either population in these strata. In fact, AAT in Q4 was smaller in the Japanese men, regardless of waist circumference stratification and the exclusion of outliers in waist circumference. This difference may be caused by the Caucasian men's negatively skewed waist circumference distribution. However, we were able to demonstrate that the mean values of VAT were larger in the Japanese than Caucasian men, and that VSR was significantly larger in the Japanese than Caucasian men in all waist circumference strata.

The strengths of our study are; (1) direct comparison in a standardized manner; (2) randomly sampled participants from general populations; and (3) narrow age-range of 40–49 years exempting us from age adjustment. There was actually no significant age difference between the Japanese and Caucasian men in any strata or overall.

The weakness of our study is the lack of women. Park et al.8 reported larger proportion of VAT in AAT in women, but no significant difference in VAT itself. They also reported a positive interaction between age and race in women. Although they reported no interaction in men, a similar interaction may have been observed in men if we had a broader age-range in our study.

In conclusion, Japanese men have larger VAT and VSR than Caucasian men across the same level of waist circumference. In multiethnic studies, difference in abdominal fat distribution should be considered in exploring factors related to obesity.

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References

  1. Fujimoto WY, Bergstrom RW, Boyko EJ, Chen KW, Leonetti DL, Newell-Morris L et al. Visceral adiposity and incident coronary heart disease in Japanese-American men. The 10-year follow-up results of the Seattle Japanese-American community diabetes study. Diabet Care 1999; 22: 1808–1812. | ISI | ChemPort |
  2. Hayashi T, Boyko EJ, Leonetti DL, McNeely MJ, Newell-Morris L, Kahn SE et al. Visceral adiposity is an independent predictor of incident hypertension in Japanese Americans. Ann Intern Med 2004; 140: 992–1000. | PubMed | ISI |
  3. Boyko EJ, Fujimoto WY, Leonetti DL, Newell-Morris L. Visceral adiposity and risk of type 2 diabetes: a prospective study among Japanese Americans. Diabetes Care 2000; 23: 465–471. | PubMed | ISI | ChemPort |
  4. Hayashi T, Boyko EJ, Leonetti DL, McNeely MJ, Newell-Morris L, Kahn SE et al. Visceral adiposity and the risk of impaired glucose tolerance: a prospective study among Japanese Americans. Diabetes Care 2003; 26: 650–655. | PubMed | ISI |
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  6. Despres JP, Couillard C, Gagnon J, Bergeron J, Leon AS, Rao DC et al. Race, visceral adipose tissue, plasma lipids, and lipoprotein lipase activity in men and women: the health, risk factors, exercise training, and genetics (HERITAGE) family study. Arterioscler Thromb Vasc Biol 2000; 20: 1932–1938. | PubMed | ISI | ChemPort |
  7. Keller C, Chintapalli K, Lancaster J. Correlation of anthropometry with CT in Mexican-American women. Res Nurs Health 1999; 22: 145–153. | Article | PubMed | ISI | ChemPort |
  8. Park YW, Allison DB, Heymsfield SB, Gallagher D. Larger amounts of visceral adipose tissue in Asian Americans. Obes Res 2001; 9: 381–387. | PubMed | ISI | ChemPort |
  9. Tanaka S, Horimai C, Katsukawa F. Ethnic differences in abdominal visceral fat accumulation between Japanese, African-Americans, and Caucasians: a meta-analysis. Acta Diabetol 2003; 40: S302–S304. | Article | PubMed | ISI |
  10. Newell-Morris LL, Treder RP, Shuman WP, Fujimoto WY. Fatness, fat distribution, and glucose tolerance in second-generation Japanese-American (Nisei) men. Am J Clin Nutr 1989; 50: 9–18. | PubMed | ChemPort |
  11. Diabetes Prevention Program Research Group. The diabetes prevention program. Design and methods for a clinical trial in the prevention of type 2 diabetes. Diabet Care 1999; 22: 623–634.
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Acknowledgements

This research was supported by Grant-in-aid for young scientists ((B):16790335) and Grant-in-aid ((A):13307016) by the Japanese Ministry of Education, Culture, Sports, Science and Technology, and National Institute of Health (1R01 HL68200).

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