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 .
Vitamin requirements for the treatment of hyperhomocysteinemia in humans.
We have previously shown that a modest vitamin supplement containing folic acid , vitamin B-12 and vitamin B-6 is effective in reducing elevated plasma homocysteine concentrations . The effect of supplementation of the individual vitamins on moderate hyperhomocysteinemia has now been investigated in a placebo-controlled study . One hundred men with hyperhomocysteinemia were r and omly assigned to five groups and treated with a daily dose of placebo , folic acid ( 0.65 mg ) , vitamin B-12 ( 0.4 mg ) , vitamin B-6 ( 10 mg ) or a combination of the three vitamins for 6 wk . Folic acid supplementation reduced plasma homocysteine concentrations by 41.7 % ( P < 0.001 ) , whereas the daily vitamin B-12 supplement lowered homocysteine concentrations by 14.8 % ( P < 0.01 ) . The daily pyridoxine dose did not reduce significantly plasma homocysteine concentrations . The combination of the three vitamins reduced circulating homocysteine concentrations by 49.8 % , which was not significantly different ( P = 0.48 ) from the reduction achieved by folate supplementation alone . Our results indicate that folate deficiency may be an important cause of hyperhomocysteinemia in the general population
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 .