Recently it has been reported that the estimated glomerular filtration rate (eGFR) is higher in habitual coffee consumers than in noncoffee consumers. However, the causality remains unclear. Therefore, we conducted a clinical trial to investigate the effects of coffee consumption on kidney function. Nineteen asymptomatic nonsmokers aged 21–27 years old participated in this study. They consumed coffee (18 g coffee beans/450 mL per day) or green tea as a comparator for 2 weeks in a crossover design. Although creatinine-based eGFR was not affected after consuming either beverage, all cystatin-C-based eGFRs determined using five different equations were significantly increased after coffee consumption (means: 5.0–7.7%), but not after green tea consumption (means: 0.1–1.6%). Serum adiponectin and magnesium levels increased significantly after coffee consumption (means: 13.6% and 4.3%, resp.), but not after green tea consumption. These findings suggest that even a short period of coffee consumption may increase cystatin-C-based eGFR, along with favorable changes in serum adiponectin, in healthy young adults.

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Regular food intake plays a pivotal role in normal glucose homeostasis. However, few studies have evaluated the level of fasting glucose in individuals with skipping breakfast, which theoretically means lack of supplementary energy and increased risk of subsequent hypoglycemia. We examined the prevalence of suspected habitual skipping breakfast (SHSB) (skipping at least three times /week), roughly assessed with a simple question, and fasting plasma glucose level, cardiovascular risk factors, and lifestyle factors in a cross-sectional study of 2,331 asymptomatic adults who had never been treated with insulin or oral medications for diabetes. The overall prevalence of SHSB was 16.3% (men 20.1%, women 9.4%, P<0.0001, χ2 test). Compared with normal fasting glucose, impaired fasting glucose (IFG) (100-125 mg/dl), but not high fasting glucose (≥126 mg/dL), was significantly associated with SHSB and this association remained after adjustment for relevant confounders [Odds Ratio (95% CI): 1.75 (1.33-2.30) and 2.10 (0.93- 4.71), respectively]. Age (inversely), current smoking, late dinner before sleeping, infrequent exercise, and high C-reactive protein (≥1.8 mg/L) were simultaneously associated with SHSB independently of each other. In a subgroup of subjects who underwent a 75g oral glucose tolerance test (n=1,315) of pre-diabetes groups, isolated IFG (n=272) was only significantly associated with SHSB. Current results suggest that IFG, subtle inflammatory state, and unfavorable lifestyle factors may be associated with the habit of skipping breakfast in asymptomatic adults. Causality and detailed mechanisms remain to be clarified in further studies

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