RESULTS The meta- analysis of observational studies showed a weaker slope of dose-response relations than the meta- analysis of RCTs .
The obtained dose-response estimate between vitamin B-12 intake and status provides complementary evidence to underpin recommendations for a vitamin B-12 intake of population
BACKGROUND Many r and omized controlled trials ( RCTs ) and observational studies have provided information on the association between vitamin B-12 intake and biomarkers .
The use of these data to estimate dose-response relations provides a useful means to summarize the body of evidence .
OBJECTIVE We systematic ally review ed studies that investigated vitamin B-12 intake and biomarkers of vitamin B-12  status and estimated dose-response relations with the use of a meta- analysis .
A controlled trial of homocysteine lowering and cognitive performance.
BACKGROUND The results of observational studies suggest that plasma homocysteine concentrations are inversely related to cognitive function in older people . Our objective was to test the hypothesis that lowering the plasma homocysteine concentration improves cognitive function in healthy older people . METHODS We conducted a two-year , double-blind , placebo-controlled , r and omized clinical trial involving 276 healthy participants , 65 years of age or older , with plasma homocysteine concentrations of at least 13 micromol per liter .  Homocysteine-lowering treatment was a daily supplement containing folate ( 1000 microg ) and vitamins B12 ( 500 microg ) and B6 ( 10 mg ) . Tests of cognition were conducted at baseline and after one and two years of treatment . Treatment effects were adjusted for baseline values , sex , and education . RESULTS On average , during the course of the study , the plasma homocysteine concentration was 4.36 micromol per liter ( 95 percent confidence interval , 3.81 to 4.91 micromol per liter ) lower in the vitamin group than in the placebo group ( P<0.001 ) . Overall , there were no significant differences between the vitamin and placebo groups in the scores on tests of cognition . CONCLUSIONS The results of this trial do not support the hypothesis that homocysteine lowering with B vitamins improves cognitive performance . ( Australian Clinical Trials registry number , ACTR NO 12605000030673 . )
RESULTS The meta- analysis of observational studies showed a weaker slope of dose-response relations than the meta- analysis of RCTs .
The obtained dose-response estimate between vitamin B-12 intake and status provides complementary evidence to underpin recommendations for a vitamin B-12 intake of population
BACKGROUND Many r and omized controlled trials ( RCTs ) and observational studies have provided information on the association between vitamin B-12 intake and biomarkers .
The use of these data to estimate dose-response relations provides a useful means to summarize the body of evidence .
OBJECTIVE We systematic ally review ed studies that investigated vitamin B-12 intake and biomarkers of vitamin B-12  status and estimated dose-response relations with the use of a meta- analysis .