Yunsuk Koh

Niacin increased glucose, insulin, and C-peptide levels in sedentary nondiabetic postmenopausal women.

The current study examined the effects of niacin and a single bout of aerobic exercise on plasma glucose, insulin, and C-peptide in sedentary, nondiabetic postmenopausal women. As a crossover design, 17 participants underwent four different trials: rest during the no-niacin condition (R), exercise during the no-niacin condition (E), rest during the with-niacin condition (RN), and exercise during the with-niacin condition (EN). All participants took 1,000 mg/day of extended-release niacin for 4 weeks during the with-niacin conditions (RN and EN). The exercise treatment consisted of a single bout of treadmill walking at 60% heart rate reserve until 400 kcal were expended. Blood samples were collected at 24 hours after each trial and analyzed for changes in plasma glucose, insulin, and C-peptide. A two by two analysis of variance was used to examine the changes in dependent variables, and the Bonferroni adjustment was employed as the post hoc test. The level of statistical significance was set at P<0.05. There was no significant interaction between exercise and niacin, nor was there a main effect of exercise for changes in glucose, insulin, or C-peptide. However, there was a significant main effect for niacin as mean glucose, insulin, and C-peptide values significantly increased with niacin; glucose increased 10.6% (P=0.001), from 95.03±10.67 mg/dL to 105.07±13.56 mg/dL; insulin increased 61.8% (P=0.001), from 16.98±12.49 μU/mL to 27.48±14.84 μU/mL; and C-peptide increased 46.1% (P=0.001), from 1.65±0.75 ng/mL to 2.41±0.97 ng/mL. Although niacin was generally well tolerated, given its adverse effects on glucose, insulin, and C-peptide profiles, the use of niacin should be done so with caution and under medical supervision.

Responses of inflammatory cytokines following moderate intensity walking exercise in overweight or obese individuals

This study investigated the effects of a 4-week moderate intensity walking exercise on the levels of C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), and adiponectin in overweight or obese individuals. Twenty-seven (13 men and 14 women) physically inactive, over-weight or obese (body mass index>25.0 kg/m2) individuals participated in the study. Each participant was randomly assigned to either exercise (EX; n=15) or control (CON; n=12) group. The EX group performed moderate intensity walking exercise on a treadmill for 60 min at 70% of maximal heart rate for 4 weeks (3 days/wk). Overnight fasting blood samples were collected before and after the study period (Pre and Post) to analyze the levels of pro-/anti-inflammatory cytokines such as CRP, TNF-α, and adiponectin. CRP and adiponectin as well as body weight and body composition were not significantly altered following the 4-week exercise intervention. However, there was a significant group×time interaction for TNF-α. The post hoc test revealed that the level of TNF-α significantly decreased only in EX (EX: mean±standard deviation, Pre 55.18±6.57 pg/mL, Post 50.31±6.22, P=0.018 vs. CON: Pre 55.5±5.88, Post 58.19±6.48, P=0.25). EX Post was also significantly lower as compared to CON Post (P=0.0074). Although there was no change in body weight or fat mass, the 4-week aerobic exercise training was long enough to decrease the level of TNF-α, indicating physical activity may improve level of inflammation independently from the change in fat mass. The current study also confirmed previous research suggesting that longer period of exercise training accompanied by weight loss may be required to induce significant changes in CRP and adiponectin.

Oxidized Low-Density Lipoprotein and Cell Adhesion Molecules Following Exercise Training

Elevated oxidized low-density lipoprotein (ox-LDL) and cell adhesion molecules are associated with inflammation and atherosclerosis. The role of exercise in circulating ox-LDL, enzyme mediators, and cell adhesion molecules are not clearly understood in obesity. As a randomized controlled design, 27 obese (BMI>30 kg/m2) sedentary men (N=13) and women (N=14) were randomly assigned to either an exercise (N=15) or a control (N=12) group. The exercise group performed a 60-min supervised treadmill exercise at moderate intensity (70% of HRmax) for 3 days per week for 4 weeks, while the control group did not exercise. Overnight fasting blood samples were collected before and after the study period to analyze serum lipids, lipoprotein-cholesterol, ox-LDL, 12- and 15-lipoxygenases, myeloperoxidase (MPO), and soluble vascular cell adhesion molecules-1 and intercellular adhesion molecule-1. Moderate-intensity exercise training lowered both ox-LDL (from 44.76±1.99 to 38.51±1.99 U/L, p=0.032) and MPO (from 31.48±2.20 to 23.09±2.20 ng/mL, p=0.010), without significantly altering body weight, other parameters of serum lipids and lipoproteins, or soluble cell adhesion molecules. Moderate intensity exercise training reduced the levels of ox-LDL and MPO, indicating a reduced risk for developing CVD and additional protection to the possible metabolic complications associated with obesity.