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 .
Effect of oral vitamin B-12 with or without folic acid on cognitive function in older people with mild vitamin B-12 deficiency: a randomized, placebo-controlled trial.
BACKGROUND Vitamin B-12 deficiency is associated with cognitive impairment in older people . However , evidence from r and omized trials of the effects of vitamin B-12 supplementation on cognitive function is limited and inconclusive . OBJECTIVE The objective was to investigate whether daily supplementation with high doses of oral vitamin B-12 alone or in combination with folic acid has any beneficial effects on cognitive function in persons aged > /=70 y with mild vitamin B-12 deficiency . DESIGN In a double-blind , placebo-controlled trial , 195 subjects were r and omly assigned to receive 1000 microg vitamin B-12 , 1000 microg vitamin B-12 + 400 microg folic acid , or placebo for 24 wk . Vitamin B-12 status was assessed on the basis of methylmalonic acid , total homocysteine ( tHcy ) , and holotranscobalamin ( holoTC ) concentrations before and after 12 and 24 wk of treatment . Cognitive function was assessed before and after 24 wk of treatment with the use of an extensive neuropsychologic test battery that included the domains of attention , construction , sensomotor speed , memory , and executive function . RESULTS Vitamin B-12 status did not change significantly after treatment in the placebo group ; however , oral vitamin B-12 supplementation corrected mild vitamin B-12 deficiency .  Vitamin B-12 + folic acid supplementation increased red blood cell folate concentrations and decreased tHcy concentrations by 36 % . Improvement in memory function was greater in the placebo group than in the group who received vitamin B-12 alone ( P = 0.0036 ) . Neither supplementation with vitamin B-12 alone nor that in combination with folic acid was accompanied by any improvement in other cognitive domains . CONCLUSION Oral supplementation with vitamin B-12 alone or in combination with folic acid for 24 wk does not improve cognitive function
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 .