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 .
Breakfast cereal fortified with folic acid, vitamin B-6, and vitamin B-12 increases vitamin concentrations and reduces homocysteine concentrations: a randomized trial.
BACKGROUND High homocysteine and low B vitamin concentrations have been linked to the risk of vascular disease , stroke , and dementia and are relatively common in older adults . OBJECTIVE We assessed the effect of breakfast cereal fortified with folic acid , vitamin B-6 , and vitamin B-12 on vitamin and homocysteine status . DESIGN A r and omized , double-blind trial was conducted in 189 volunteers aged 50 - 85 y. The subjects had no history of hypertension , anemia , asthma , cancer , or cardiovascular or digestive disease and did not regularly consume multiple or B vitamin supplements or highly fortified breakfast cereal . Subjects were r and omly assigned to consume 1 cup ( 0.24 L ) breakfast cereal fortified with 440 microg folic acid , 1.8 mg vitamin B-6 , and 4.8 microg vitamin B-12 or placebo cereal for 12 wk . Blood was drawn at 0 , 2 , 12 , and 14 wk . Methionine-loading tests were conducted at baseline and week 14 . RESULTS Final baseline-adjusted plasma homocysteine concentrations were significantly lower and B vitamin concentrations were significantly higher in the treatment group than in the placebo group ( P < 0.001 ) . The percentage of subjects with plasma folate concentrations < 11 nmol/L decreased from 2 % to 0 % , with vitamin B-12 concentrations < 185 pmol/L from 9 % to 3 % , with vitamin B-6 concentrations < 20 nmol/L from 6 % to 2 % , and with homocysteine concentrations > 10.4 micromol/L ( women ) or > 11.4 micromol/L ( men ) from 6.4 % to 1.6 % . The percentage of control subjects with values beyond these cutoff points remained nearly constant or increased . CONCLUSIONS In this relatively healthy group of volunteers , consumption of 1 cup fortified breakfast cereal daily significantly increased B vitamin and decreased homocysteine concentrations , including post-methionine-load homocysteine concentrations
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 .