BACKGROUND Carotenoids may reduce the risk for diabetes mellitus, but little is known about the association of insulin resistance with serum carotenoids in non-diabetic subjects. This study aimed to investigate whether the homeostasis model assessment-insulin resistance (HOMA-IR) index would be lower in the presence of high serum carotenoid concentrations in non-diabetic subjects. METHODS A total of 812 subjects (256 males and 556 females) who had received health examinations in 2003 participated in the study. The associations of the serum-carotenoid concentrations and HOMA-IR were evaluated cross-sectionally. The multivariate-adjusted geometric means of HOMA-IR by the tertiles of the serum carotenoid concentration were calculated after adjusting for age, body mass index, systolic blood pressure, total cholesterol, triacylglycerols, current tobacco use, regular alcohol intake, exercise habits and total energy intake. Associations among high HOMA-IR (3.0+ mU×mmol/L 2 ) across tertiles of serum carotenoid concentration were assessed by tests for logistic regression analysis. RESULTS In male subjects, the multivariate adjusted geometric mean of HOMA-IR was inversely associated with the serum β -cryptoxanthin concentrations. In female subjects, an inverse association of the serum carotenoid concentration and HOMA-IR was observed in lycopene, β -cryptoxanthin, and zeaxanthin. The confounding factor-adjusted odds ratios (OR) for high HOMA-IR on the highest tertiles of serum α -carotene, β -carotene, β -cryptoxanthin, and zeaxanthin were 0.18 [95% confidence interval (CI): 0.06-0.52], 0.22 (95% CI: 0.07-0.67), 0.34 (95% CI: 0.12-0.96), and 0.30 (95% CI: 0.11-0.79), respectively, in male subjects. On the other hand, in female subjects, the adjusted OR for high HOMA-IR on the highest tertiles of serum lycopene and β -cryptoxanthin were 0.39 (95% CI: 0.21-0.73) and 0.51 (95% CI: 0.28-0.95), respectively. CONCLUSIONS The serum antioxidant carotenoids were inversely associated with HOMA-estimated insulin resistance in non-diabetic subjects.
BACKGROUND: Many studies have reported that the consumption of alcohol induces the generation of free radicals. Moreover, recent studies suggest that serum gamma-glutamyltransferase ( γ -GTP) within its normal range might be an early marker of oxidative stress. In this study, we tested the hypothesis that serum antioxidant carotenoids would be inversely associated with serum γ -GTP in alcohol drinkers within normal liver function. METHODS: A total of 266 Japanese men who had received health examination in 2003 participated in the study. The associations of serum γ -GTP and serum-carotenoid concentrations stratified by alcohol intake levels were evaluated cross-sectionally. The participants were divided into three groups according to their ethanol intake level (non-drinker, less than 1 g/day; light drinker, 1-25 g/day; and moderate and heavy drinkers, 25+ g/day). The multivariate-adjusted geometric means of the serum γ -GTP concentrations in each tertile of the serum-carotenoid concentrations were calculated after adjustment for ethanol intake, age, body mass index, total cholesterol, triacylglycerols, current tobacco use, and habitual exercise. RESULTS: The serum γ -GTP concentrations were significantly high in accordance with the ethanol intake level. In moderate and heavy drinkers, the multivariate-adjusted geometric means of serum γ -GTP concentrations were significantly low in accordance with the tertiles of the serum lycopene, α -carotene, β -carotene, and β -cryptoxanthin concentrations. CONCLUSIONS: The serum antioxidant carotenoids were inversely associated with alcohol-induced increases of serum γ -GTP in moderate and heavy drinkers within normal liver function.
Recent epidemiologic studies have demonstrated that high dietary consumption of fruit and vegetables results in lower risks of certain cancers and cardiovascular disease.1,2) There is accumulating evidence that these effects of fruit and vegetables attribute to antioxidants nutrients such as carotenoids, vitamins, and phenolic phytochemicals. Recent studies have shown that antioxidant vitamins and carotenoids may have a protective effect against diabetes mellitus. 3-6)Satsuma mandarin (Citrus unshiu MARC.) is the most frequently consumed domestic fruit in Japan.7) Numerous antioxidants such as b-cryptoxanthin, vitamins, and flavonoids exist in pulp of this fruit.8-10) Previously, we found inverse association of the prevalence of diabetes mellitus with frequency of Satsuma mandarin intake based on data from 6049 participants on a self-administered questionnaire in crosssectionally.11) Furthermore, very recently, Kamata et al. reported that the chronic administration of Satsuma mandarin fruit extract improved endothelial dysfunction in the aorta in streptozotocin (STZ)-induced diabetic rats without lowering plasma cholesterol.12) Hyperglycemia increases the generation of free radicals by glucose auto-oxidation. [13][14][15] Oxidative stress resulting from the increased production of reactive oxygen species plays a key role in the development of diabetic mellitus or its complications. [16][17][18][19][20] Therefore, Satsuma mandarin would be expected to protect against the development of diabetes mellitus or the pathogenesis of diabetic complications.On the other hand, the liver plays an important role in glucose metabolism, and it is a major site of insulin clearance. 21,22) Oxidative stress induced by hyperglycemia may lead to liver cell damage. Wohaieb et al. found that the antioxidant enzyme activities and glutathione level in STZ-induced diabetic rat liver significantly decreased compared with those in control rats and that the impairment of the antioxidant defense system in STZ-induced diabetic rat liver was reversed by insulin treatment.23) These results indicate that oxidative stress induced by hyperglycemia may lead to liver dysfunction.In this study, we expected that Satsuma mandarin would inhibit liver injury induced by hyperglycemia and investigated the effects of the chronic administration of Satsuma mandarin on the antioxidant defense system: i.e., the superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione levels in an STZ-induced type-1 diabetic model rat liver. MATERIALS AND METHODSSatsuma mandarin (Citrus unshiu MARC.) juice was purchased from the Ehime Beverage, Inc. (Ehime, Japan). The concentrated Satsuma mandarin juice was freeze-dried and mixed with a standard commercial diet (MF diet, Oriental Yeast, Tokyo, Japan) at 1, 3 w/w% (fruit extract-containing diet).Male Wistar rats (5 weeks old and with a 150-170 g body weight) were purchased from CLEA Japan, Inc. (Tokyo, Japan). All animals were maintained in an environmentally controlled roo...
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