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 .
B-vitamins reduce plasma levels of beta amyloid
Elevated plasma homocysteine ( tHcy ) is a risk factor for Alzheimer 's disease ( AD ) , and thus B vitamins may have a role in the prevention of AD . The objective of this study was to determine if tHcy lowering vitamins decrease the circulating levels of A-beta protein 1 - 40 ( A beta 40 ) . We r and omized 299 older men to treatment with 2 mg of folate , plus 25 mg of B6 and 400 microg of B12 , or placebo . After 2 years of treatment the mean ( S.E. ) increase of A beta 40 was 7.0 pg/ml ( 8.4 ) in the vitamin group ( 4.9 % ) , and 26.8 pg/ml ( 7.7 ) ( 18.5 % ) in the placebo group . We conclude that B vitamins may decrease the plasma level of A beta 40 and have a role in the prevention of AD
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 .