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 .
Oral vitamin B12 supplementation reduces plasma total homocysteine concentration in women in India.
People in India have a high prevalence of low vitamin B12 status and high plasma total homocysteine ( tHcy ) concentrations . In a proof of principle trial , we studied the effect of oral vitamin B12 ( 500 microg ) and /or 100 g cooked green leafy vegetables ( GLV ) every alternate day in a 2x2 factorial design over a 6-week period . Forty-two non-pregnant vegetarian women ( age 20 - 50 years ) were r and omly allocated to four study groups . Clinical measurements were made at the beginning and at the end of the study , and blood sample s were collected before , and 2 and 6 weeks after commencement of intervention . Forty women completed the trial . Twenty-six women had low vitamin B12 status ( < 150 pmol/L ) and 24 had hyperhomocysteinemia ( > 15 micromol/L ) . GLV supplementation did not alter plasma folate or tHcy .  Vitamin B12 supplementation increased plasma vitamin B12 concentration ( 125 to 215 pmol/L , p < 0.05 ) and reduced tHcy concentration ( 18.0 to 13.0 micromol/L , p < 0.05 ) within first 2 weeks , both of which remained stable for the next 4 weeks . Plasma vitamin B12 and tHcy concentrations did not change in those who did not receive vitamin B12 , and there was no change in plasma folate concentration in any of the groups . Blood haemoglobin concentration increased marginally within first two weeks in those women who received vitamin B12 ( by 3 g/L , p < 0.05 ) and the number of women with macrocytosis decreased from 2 to zero . There was no change in vibration sensory threshold during the period of the study . High-dose per oral vitamin B12 supplementation significantly reduced plasma tHcy within 2 weeks but did not achieve normal plasma tHcy concentration even after 6 weeks . People in India have a high prevalence of low vitamin B12 status and high plasma total homocysteine ( tHcy ) 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 .