Objectives:
Soy isoflavones may have beneficial roles as antioxidants and phytoestrogens. Dietary intake varies widely across populations: very high in Japan but low in North America. We measured the concentrations of daidzein and genistein in the serum of Japanese men and women and evaluated their associations with metabolic markers.
Methods:
Serum samples were obtained from a population based sample of 94 Japanese men (mean age 45.3), and 142 Japanese women (mean age 66.6; 97% were post-menopausal). Isoflavones were analyzed after extraction and derivatization using GC-MS. Concentrations of daidzein and genistein were summed to obtain total isoflavone concentrations.
Results:
Isoflavone concentrations were very high among the Japanese. Median values (nM) for men: 558, 452 and 86 and for women 660, 494 and 150 (total isoflavones, genistein and daidzein, respectively). Spearman correlation coefficients for the isoflavones with multiple outcomes among Japanese men and women are shown in the table.
No significant (p<0.05) associations were observed among the men but borderline negative associations were observed for total isoflavones (p=0.063) and genistein (p=0.063) with LDLc. Among women there was a significant association between total isoflavones (p=0.041) and daidzein (p=0.006) with HDLc. Borderline significant associations were also observed for total isoflavones (p=0.068) and genistein (p=0.061) with glucose.
Discussion:
The concentrations of isoflavones are high in the Japanese, approximately 50 times greater than those of N. Americans. Associations between the isoflavones and various outcomes were very weak for the Japanese men. This possibly reflects a plateau of isoflavone concentration has been reached that precludes observing any associations. Although, many correlations were calculated the positive associations of total isoflavones and daidzein with HDLc among women may be real. HDLc concentrations are high in Japanese women which may reflect the estrogenic actions of isoflavones.
Isoflavone consumption and subsequent risk of hepatocellular carcinoma in a population-based prospective cohort of Japanese men and women