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 .
Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study.
BACKGROUND Low vitamin B-12 status is prevalent among the elderly , but few studies have examined the association between vitamin B-12 status and intake . OBJECTIVE We hypothesized that vitamin B-12 concentrations vary according to intake source . DESIGN Plasma concentrations and dietary intakes were assessed cross-sectionally for 2999 subjects in the Framingham Offspring Study . The prevalence of vitamin B-12 concentrations < 148 , 185 , and 258 pmol/L was examined by age group ( 26 - 49 , 50 - 64 , and 65 - 83 y ) , supplement use , and the following food intake sources : fortified breakfast cereal , dairy products , and meat . RESULTS Thirty-nine percent of subjects had plasma vitamin B-12 concentrations < 258 pmol/L , 17 % had concentrations < 185 pmol/L , and 9 % had concentrations < 148 pmol/L , with little difference between age groups . Supplement users were significantly less likely than non-supplement-users to have concentrations < 185 pmol/L ( 8 % compared with 20 % , respectively ) . Among non-supplement-users , there were significant differences between those who consumed fortified cereal > 4 times/wk ( 12 % ) and those who consumed no fortified cereal ( 23 % ) and between those in the highest and those in the lowest tertile of dairy intake ( 13 % compared with 24 % , respectively ) , but no significant differences by meat tertile . Regression of plasma vitamin B-12 on log of intake , by source , yielded significant slopes for each contributor adjusted for the others . For the total group , b = 40.6 for vitamin B-12 from vitamin supplements . Among non-supplement-users , b = 56.4 for dairy products , 35.2 for cereal , and 16.7 for meat . Only the meat slope differed significantly from the others . CONCLUSIONS In contrast with previous reports , plasma vitamin B-12 concentrations were associated with vitamin B-12 intake . Use of supplements , fortified cereal , and milk appears to protect against lower concentrations . Further research is needed to investigate possible differences in bioavailability
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 .