Marc P. McRae

Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials

OBJECTIVE Vitamin C has been shown to be an effective therapeutic for reducing total serum cholesterol, but epidemiologic studies have determined that low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol are actually better predictive measures of coronary heart disease risk. Therefore, the purpose of this study was to provide a comprehensive meta-analysis of randomized controlled trials to investigate the effect of vitamin C supplementation on LDL and HDL cholesterol as well as triglycerides in patients with hypercholesterolemia. METHODS Thirteen randomized controlled trials published between 1970 and June 2007 were identified using Medline and a manual search. From the 13 trials, 14 separate group populations with hypercholesterolemia and who were supplemented with at least 500 mg/d of vitamin C for between 3 and 24 weeks were entered into the meta-analysis. This meta-analysis used a random-effects model; and the overall effect sizes were calculated for changes in LDL and HDL cholesterol, as well as triglyceride concentrations. RESULTS The pooled estimate of effect for vitamin C supplementation on LDL and HDL cholesterol was -7.9 mg/dL (95% confidence interval [CI], -12.3 to -3.5; P = .000) and 1.1 mg/dL (95% CI, -0.2 to 2.3; not significant), respectively. The pooled estimate of effect for vitamin C supplementation on triglycerides was -20.1 mg/dL (95% CI, -33.3 to -6.8; P < .003). CONCLUSION Supplementation with at least 500 mg/d of vitamin C, for a minimum of 4 weeks, can result in a significant decrease in serum LDL cholesterol and triglyceride concentrations. However, there was a nonsignificant elevation of serum HDL cholesterol.

High-dose folic acid supplementation effects on endothelial function and blood pressure in hypertensive patients: a meta-analysis of randomized controlled clinical trials

OBJECTIVE Folic acid supplementation has been shown to be an effective agent for improving endothelial function, a prognostic factor for cardiovascular disease; but its effects on systolic and diastolic blood pressure in hypertensive individuals has been met with mixed results. Therefore, the purpose of this study was to provide a comprehensive meta-analysis of randomized controlled trials to investigate the effect of high-dose folic acid supplementation on blood pressure and endothelial function in hypertensive patients. METHODS Twelve randomized controlled trials published between 1970 and December 2007 were identified using Medline and a manual search. All 12 studies used hypertensive subjects who were supplemented with at least 5000 mug/d of folic acid for between 2 and 16 weeks. Three separate meta-analyses were carried out using a random-effects model, and the overall effect sizes were calculated for changes in systolic and diastolic blood pressures and for changes in endothelial function as measured through the percentage of change in flow-mediated dilation. RESULTS The pooled estimate of effect of folic acid supplementation on systolic and diastolic blood pressure was -2.03 mm Hg (95% confidence interval [CI], -3.63 to -0.43; P = .04) and 0.01 mm Hg (95% CI, -1.12 to 1.13; not significant), respectively. The pooled estimate of effect of folic acid supplementation on change in flow-mediated dilation was 1.61% (95% CI, 1.27 to 1.96; P = .000). CONCLUSION Based upon the studies used in this meta-analysis, supplementation with at least 5000 mug/d of folic acid, for a minimum of 6 weeks, can lower systolic blood pressure slightly; but the real clinical benefit is achieved through improved endothelial function.

The efficacy of vitamin C supplementation on reducing total serum cholesterol in human subjects: a review and analysis of 51 experimental trials

OBJECTIVE Observational studies in humans have shown an inverse relationship between plasma vitamin C concentration and total serum cholesterol. However, experimental studies have shown inconsistent results regarding the ability of vitamin C to reduce total serum cholesterol. METHODS Published reports of trials studying the effects of vitamin C on serum lipids were identified by a search of Medline from 1966 to 2004. Data from 51 experimental studies comprising of 1666 pooled subjects were selected for analysis. RESULTS A very strong negative association was observed between baseline total serum cholesterol and the percent change in cholesterol (r = -0.585, p<0.001). When subjects were divided into 4 groups based on their baseline total serum cholesterol levels, the following weighted mean percent changes in cholesterol from baseline were observed: normal cholesterol (<199mg/dl): 0.91+/-6.8% (n=508); borderline high cholesterol (200-239mg/dl): 3.90+/-5.78% (n=605); high cholesterol (240-279mg/dl): 11.40+/-7.96% (n=300); severe cholesterol (>280mg/dl): 14.30+/-8.36% (n=253). A significant inverse relationship was found between the baseline plasma vitamin C concentrations and mean percent change in total cholesterol from baseline (r = -0.500, p<0.005). It was also observed that the high and severe baseline cholesterol groups possessed lower baseline plasma vitamin C concentrations than those in the normal cholesterol groups (0.79 and 0.55 versus 1.24 mg/dl respectively). CONCLUSION This finding strengthens the hypothesis that the cholesterol lowering and cardio-protective benefit of vitamin C supplementation may be in its ability to elevate plasma vitamin C concentrations in those patients who initially possess lower than normal vitamin C plasma concentrations.

Is vitamin C an effective antihypertensive supplement: a review and analysis of the literature

OBJECTIVE Hypertension is a common condition with high mortality from associated diseases. Epidemiological evidence suggests that a dietary deficiency of vitamin C may be a risk factor for hypertension. However the literature on vitamin C interventional trials appears divided on the efficacy of vitamin C utilization clinically. METHODS A literature search and review of published trials using vitamin C in treating patients with hypertension was undertaken. Relevant references were located using MEDLINE (1966-2005) and the bibliographies of located articles. RESULTS Thirteen trials making up 14 separate groups were identified and analyzed providing a pooled population of 284 hypertensive patients (52% female), with a weighted mean age of 58.8 +/- 9.5 years. Median vitamin C dose and study intervention duration was 500mg/day and 6 weeks respectively. The weighted mean baseline and post treatment systolic blood pressures across all 14 groups were 149.6 +/- 11.1 and 145.7 +/- 11.0 mmHg respectively. This represented a systolic blood pressure decrease of 3.9 mmHg. Seven of the 14 groups ascertained statistically significant reductions (p < .05) in systolic blood pressures. However only 2 of the 14 groups found significant reductions in diastolic blood pressure. The weighted mean baseline and post treatment diastolic blood pressures across all 14 groups were 84.6 +/- 4.4 and 82.5 +/- 4.1 mmHg respectively. This represented a diastolic blood pressure decrease of 2.1 mmHg. CONCLUSION Vitamin C supplementation in hypertensive patients appears to possess modest effects on reducing systolic blood and diastolic blood pressure.

Health Benefits of Dietary Whole Grains: An Umbrella Review of Meta-analyses

Objective: The purpose of this study is to review the effectiveness of the role of whole grain as a therapeutic agent in type 2 diabetes, cardiovascular disease, cancer, and obesity. Methods: An umbrella review of all published meta‐analyses was performed. A PubMed search from January 1, 1980, to May 31, 2016, was conducted using the following search strategy: (whole grain OR whole grains) AND (meta‐analysis OR systematic review). Only English language publications that provided quantitative statistical analysis on type 2 diabetes, cardiovascular disease, cancer, and weight loss were retrieved. Results: Twenty‐one meta‐analyses were retrieved for inclusion in this umbrella review, and all the meta‐analyses reported statistically significant positive benefits for reducing the incidence of type 2 diabetes (relative risk [RR] = 0.68‐0.80), cardiovascular disease (RR = 0.63‐0.79), and colorectal, pancreatic, and gastric cancers (RR = 0.57‐0.94) and a modest effect on body weight, waist circumference, and body fat mass. Significant reductions in cardiovascular and cancer mortality were also observed (RR = 0.82 and 0.89, respectively). Some problems of heterogeneity, publication bias, and quality assessment were found among the studies. Conclusion: This review suggests that there is some evidence for dietary whole grain intake to be beneficial in the prevention of type 2 diabetes, cardiovascular disease, and colorectal, pancreatic, and gastric cancers. The potential benefits of these findings suggest that the consumption of 2 to 3 servings per day (˜45 g) of whole grains may be a justifiable public health goal.

Male and female differences in variability with estimating body fat composition using skinfold calipers

OBJECTIVE Obesity is a major health problem in the United States. Skinfold measurements are routinely used in assessing outcomes in the management of obesity. The purpose of this study was to determine if sex differences in skinfold measurements would be apparent in intraobserver and interobserver reliability as well as validity when compared with bioelectrical impedance analysis (BIA) measurements. METHODS To determine intraobserver and interobserver variability, 71 male and 45 female subjects (chiropractic students) were assessed by 4 separate observers who each took 4 separate skinfold measurements. Bioelectrical impedance analysis was later conducted using a foot-to-foot technique. The average sums of the skinfold measurement and their standard deviations were calculated, and correlation coefficients between skinfold measurements and BIA techniques for male and female subjects were plotted separately to assess validity. RESULTS Men tended to have greater amounts of intraobserver and interobserver variability when compared with women, but these differences were not significant. In regard to validity, there was no significant difference between skinfold measurements and BIA when estimating percentage body fat for men; but the difference was significant for women, where BIA underestimated by 3.4%. CONCLUSIONS The differences observed in variability could be explained by the fact that there is a difference in skinfold compressibility between men and women. Physicians who are using skinfold calipers for body composition assessment should take into account these small potential differences when evaluating total body fatness.

Therapeutic Benefits of L-Arginine: An Umbrella Review of Meta-analyses

OBJECTIVE l-Arginine is a semi-essential amino acid that is the substrate for nitric oxide production by vascular endothelial and immune cells. Nitric oxide production by these cells is essential for both blood pressure regulation and immune regulation. However, there is much discrepancy in the literature when it comes to randomized controlled studies, and so this umbrella review of published meta-analyses was performed to examine the efficacy of l-arginines role as a therapeutic agent. METHODS There was an overall search of the literature from January 1, 1980 through December 31, 2015 of three separate databases-PubMed, Cochrane Library, and Cumulative Index to Nursing and Allied Health Literature-using the following search strategy: (arginine) AND (meta-analysis OR systematic review). Only English language publications were retrieved that provided quantitative statistical analysis of outcomes on blood pressure and immune function. RESULTS The 7 meta-analyses that were included in this umbrella review reported significant positive benefits for reducing systolic and diastolic blood pressure in hypertensive adults by 2.2 to 5.4 mm Hg and 2.7 to 3.1 mm Hg, respectively, reducing diastolic blood pressure in pregnant women with gestational hypertension by 4.9 mm Hg, and reducing the length of stay in the hospital for surgical patients; in addition, 2 of the 3 meta-analyses indicated a 40% reduction in the incidence of hospital-acquired infections. However, these positive results should be considered with caution because statistically significant heterogeneity was observed in 5 of the 7 meta-analyses. CONCLUSIONS Some evidence appears to support the benefit of l-arginine supplementation for reducing systolic and diastolic blood pressure in hypertensive adults and reducing the incidence of hospital-acquired infections and the length of stay in the hospital for surgical patients. Given the limitations of the included studies, interpretations should be made with caution.

Dietary Fiber Intake and Type 2 Diabetes Mellitus: An Umbrella Review of Meta-analyses

Objective: The purpose of this study was to review previously published meta‐analyses on the effectiveness of dietary fiber on type 2 diabetes. Methods: An umbrella review of all published meta‐analyses was performed. A PubMed search from January 1, 1980, to April 30, 2017, was conducted using the following search strategy: (fiber OR glucan OR psyllium) AND (meta‐analysis OR systematic review). Only English‐language publications that provided quantitative statistical analysis on type 2 diabetes, fasting blood glucose concentrations, or glycosylated hemoglobin were retrieved. Results: Sixteen meta‐analyses were retrieved for inclusion in this umbrella review. In the meta‐analyses comparing highest versus lowest dietary fiber intake, there was a statistically significant reduction in the relative risk (RR) of type 2 diabetes (RR = 0.81‐0.85), with the greatest benefit coming from cereal fibers (RR = 0.67‐0.87). However, statistically significant heterogeneity was observed in all of these meta‐analyses. In the meta‐analyses of supplementation studies using &bgr;‐glucan or psyllium fibers on type 2 diabetic participants, statistically significant reductions were identified in both fasting blood glucose concentrations and glycosylated hemoglobin percentages. Conclusion: This review suggests that those consuming the highest amounts of dietary fiber, especially cereal fiber, may benefit from a reduction in the incidence of developing type 2 diabetes. There also appears to be a small reduction in fasting blood glucose concentration, as well as a small reduction in glycosylated hemoglobin percentage for individuals with type 2 diabetes who add &bgr;‐glucan or psyllium to their daily dietary intake.

The Benefits of Dietary Fiber Intake on Reducing the Risk of Cancer: An Umbrella Review of Meta-analyses

Objective: The purpose of this study was to review previously published meta‐analyses on the effectiveness of dietary fiber on reducing the incidence of cancer. Methods: An umbrella review of all published meta‐analyses was performed. A PubMed search from January 1, 1980 to June 30, 2017 was conducted using the following search strategy: (fiber OR fibre) AND (meta‐analysis OR systematic review) AND (cancer OR carcinoma). Only English‐language publications that provided quantitative statistical analysis on cancer were retrieved. Results: Nineteen meta‐analyses comparing highest vs lowest dietary fiber intake were retrieved for inclusion in this umbrella review. There was a statistically significant reduction in the relative risk (RR) of colorectal, esophageal, gastric, and pancreatic cancer (RR = 0.52‐0.88); however, statistically significant heterogeneity was observed in the meta‐analyses on esophageal, gastric, and pancreatic cancer. There was a statistically significant reduction in the RR of breast cancer (RR = 0.85‐0.93). Conclusion: This review suggests that those consuming the highest amounts of dietary fiber may benefit from a reduction in the incidence of developing colorectal cancer, and there also appears to be a small reduction in the incidence of breast cancer.