Background and aims: Previously, we found significantly higher serum leptin in Japanese-Americans in Hawaii than Japanese in Japan. We investigated whether differences in dietary and other lifestyle factors explain higher serum leptin concentrations in Japanese living a Western lifestyle in Hawaii compared with Japanese in Japan.
Methods and results: Serum leptin and nutrient intakes were examined by standardized methods in men and women ages 40-59 years from two population samples, one Japanese-American in Hawaii (88 men, 94 women), the other Japanese in central Japan (123 men, 111 women). Multiple linear regression models were used to assess role of dietary and other lifestyle traits in accounting for serum leptin difference between Hawaii and Japan. Mean leptin was significantly higher in Hawaii than Japan (7.2 ± 6.8 vs 3.7 ± 2.3 ng/ml in men, P < 0.0001; 12.8 ± 6.6 vs 8.5 ± 5.0 in women <0.0001). In men, higher BMI in Hawaii explained over 90% of the difference in serum leptin; in women, only 47%. In multiple linear regression analyses in women, further adjustment for physical activity and dietary factors--alcohol, dietary fiber, iron--produced a further reduction in the coefficient for the difference, total reduction 70.7%; P-value for the Hawaii-Japan difference became 0.126.
Conclusion: The significantly higher mean leptin concentration in Hawaii than Japan may be attributable largely to differences in BMI. Differences in nutrient intake in the two samples were associated with only modest relationship to the leptin difference.
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