Meta-analysis studies supplements

In more recent times, large doses of vitamin C have been claimed to prevent the common cold, cure infertility, delay the onset of symptoms in acquired immunodeficiency syndrome (AIDS), and inhibit the development of gastric and cervical cancers. None of these claims have been backed by medical evidence, however. In the largest study yet done of the effect of vitamin C on the common cojd, a meta-analysis of more than 100 separate trials covering 40,000 people found no difference in the incidence of colds between those who took supplemental vitamin G regularly and those who did not. When taken during a cold, however, vitamin C does appear to decrease the cold s duration by 8%. 

Another meta-analysis has been conducted on 19 clinical trials with vitamin E supplementation and follow-up of a duration of more than one year. Nine trials were using vitamin E only without any other supplement and six of them were double-blind/placebo-controlled studies (28), The outcome of the analysis was that high dosages (>400 ILJ/d) may increase all-cause mortality and, therefore, should be avoided. Since in many studies other supplements were used concomitantly to vitamin E the authors concluded, the use of any high-dose supplement should be discouraged until evidence of efficacy is documented from appropriately designed clinical trials. ... 

At Johns Hopkins University in Baltimore, doctors collected data from twenty trials that looked at the effects of magnesium supplementation on blood pressure. They pooled the data to form one megastudy, in what is termed a meta-analysis. In six of the studies, subjects had normal blood pressure in the others, patients were hypertensive. The data came from 1,220 men and women, and the daily dose of magnesium ranged from 10 to 40 mmol (180 to 720 mg). 

This is an endogenous substance produced from adenosine triphosphate and the amino acid methionine. It is naturally involved in a range of biological processes. As a supplement, it is most studied in the treatment of depression, as well as treatment of liver disease. In a recent meta-analysis, doses of 400 mg-1600 mg per day were found to be superior to placebo and as efficacious as moderate-dose tricyclic antidepressants. A few small trials in patients with... 

Coenzyme QIO is a powerful antioxidant naturally occurring in the mitochondria of myocardium, and it is an electron carrier in the mitochondrial synthesis of ATP. Patients with heart failure have lower myocardial levels of coenzyme QIO, but supplementation has been demonstrated to have variable benefits in randomized controlled trials. One meta-analysis on the use in congestive heart failure showed improvements in stroke volume, ejection fraction, cardiac output, cardiac index, and end diastolic volume index. " Another antioxidant associated with beneficial effects in cardiac patients is lycopene, a natural constituent of tomatoes. Lycopene is the major carotenoid found in human serum, and epidemiological studies have indicated an effect of dietary supplementation in reducing heart disease. Few dietary interventions have been reported one study showed a mild but significant hypocholesterolemic effect, and another showed a significant reduction in LDL oxidation. " Animal studies show an antiatherogenic effect of DHEA, and a review of the clinical trials and studies on DHEA in males with coronary heart disease reported a favorable or neutral effect. Plasma levels of DHEA are decreased in patients with chronic heart failure in proportion to its severity. ... 

Although a few studies show a benefit of soy products on BP, the majority of evidence from clinical trials indicates that soy consumption does not significantly improve BP (Balk et al., 2005). A meta-analysis of 21 studies conducted through 2004 reported a net change of—1 mm Hg for both SBP and DBP (Balk et al., 2005). Changes in BP do not appear to be influenced by baseline BP, independent soy protein or isoflavone consumption, soy incorporated into the diet or taken as a supplement, gender, or menopausal status (Balk et al., 2005). 

To assess the relationship of Hey concentrations with vascular disease risk, a meta-analysis of observational studies was carried out, showing that elevated Hey is at most a modest independent predictor of ischemic heart disease and stroke risk in healthy populations. Studies of the impact on disease risk of genetic variants that affect blood Hey concentrations will help determine whether Hey is causally related to vascular disease, as may large randomized trials of the effects on ischemic heart disease and stroke of vitamin supplementation to lower blood Hey concentrations (Homocysteine Studies Collaboration 2002). 

Ronsmans, C., Fisher, D.J., Osmond, C., Margetts, B.M., Fall, C.H.D., and the Maternal Micronutiient Supplementation Study Group (MMSSG), 2009. Multiple micronutrient supplementation during pregnancy in low-income countries A meta-analysis of effects on stillbirths and on early and late neonatal mortality. Food and Nutrition Bulletin. 30 S547-S555. 

In order to estimate reliably the associations of homocysteine with CHD and stroke outcomes, individual participant data were collected from all observational studies of homocysteine with CHD and stroke outcomes for the Homocysteine Studies Collaboration (Homocysteine Studies Collaboration 2002). With individual participant data, the Homocysteine Studies Collaboration meta-analysis was able to examine the shape and strength of association of homocysteine with vascular disease after adjustment for bias and confounding due to other risk factors (Homocysteine Studies Collaboration 2002). After excluding individuals with prior disease at enrolment and adjustment for smoking, blood pressure and cholesterol, a 25% lower usual i.e. longterm) homocysteine concentration (about 3 pmol/L, a difference typically achieved by folic add supplementation in populations without mandatory fortification of grain products with folic acid) was associated with an 11% (95% Cl 4-17%) lower risk of CHD and a 19% (5-31%) lower risk of stroke (Homocysteine Studies Collaboration 2002). 

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