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 multivitamin supplementation
on the homocysteine and methylmalonic
acid blood concentrations in women
over the age of 60 years
Summary Background Deficiency of folic acid , vitamin B6 and /or vitamin B12 can result in elevated total plasma homocysteine concentrations ( tHcy ) , which are considered to be a risk factor for vascular disease . Studies have shown that supplementation of the three vitamins can lower tHcy even in subjects with tHcy in the normal range . Aim of the study The aim of this study was to evaluate the effect of a 6 month supplementation with vitamin B6 , B12 and folate on the concentrations of total plasma homocysteine and serum methylmalonic acid ( MMA ) of elderly women . Methods The study was design ed as a r and omized placebo controlled doubleblind trial , and 220 healthy women ( aged 60–91 years ) were involved .  The vitamin and mineral capsule contained pyridoxine ( 3.4 mg ) , folic acid ( 400 µg ) and cobalamin ( 9 µg ) in addition to other micronutrients  . Blood concentrations of folate , cobalamin , tHcy , MMA and the activity coefficient of erythrocyte alpha-aspartic aminotransferase ( alpha-EAST ) were measured at baseline and after 6 months of supplementation . Dietary intake was evaluated at the beginning and the end of the intervention by two 3–day diet records . Results Median concentrations of serum cobalamin , serum folate and erythrocyte folate increased significantly and tHcy and alpha – EAST activity ( indicative of improved status of vitamin B6 ) coefficient decreased significantly in the supplemented group . Median MMA concentration of the supplemented group was significantly lower than that of the placebo group after the intervention . The vitamin supplementation had a greater decreasing effect on the tHcy concentration of volunteers with lower vitamin and higher tHcy initial concentrations . In a linear regression model , baseline tHcy , serum folate , age and alpha – EAST activity coefficient were significantly correlated with the change in tHcy . The change in MMA in the supplement group was significantly associated to the baseline MMA values . Conclusions Our results show that a 6 month supplementation including physiological dosages of B vitamins improves the status of these nutrients and reduces tHcy in presumed healthy elderly women
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 .