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 folate, vitamin B6, vitamin B12, homocysteine, and risk of breast cancer.
BACKGROUND In several epidemiologic investigations , folate intake has appeared to reduce the elevated risk of breast cancer associated with moderate alcohol consumption . However , data relating plasma folate levels to breast cancer risk are sparse . We investigated the association between plasma folate and other vitamins with breast cancer in a prospect i ve , nested case-control study . METHODS Blood sample s were obtained during 1989 and 1990 from 32 826 women in the Nurses ' Health Study who were followed through 1996 for the development of breast cancer . We identified 712 breast cancer case patients and selected 712 individually matched control subjects .  Dietary information was obtained using food frequency question naires given in 1980 , 1984 , 1986 , and 1990 . Logistic regression was used to estimate the relative risks ( RRs ) of breast cancer ( after adjustment for potential risk factors ) , and a generalized linear model was used to calculate the Pearson correlation coefficients between plasma estimates of folate , vitamin B(6 ) , vitamin B(12 ) , and homocysteine , and intakes of folate , vitamin B(6 ) , and vitamin B(12 ) . All statistical tests were two-sided . RESULTS The multivariable RR comparing women in the highest quintile of plasma folate with those in the lowest was 0.73 ( 95 % confidence interval [ CI ] = 0.50 to 1.07 ; P(trend ) = .06 ) . The inverse association between plasma folate and breast cancer risk was highly statistically significant among women consuming at least 15 g/day ( i.e. , approximately 1 drink/day ) of alcohol ( multivariable RR = 0.11 , 95 % CI = 0.02 to 0.59 for highest versus lowest quintile ) in contrast with that of women consuming less than 15 g/day ( multivariable RR = 0.72 , 95 % CI = 0.49 to 1.05 ) . The multivariable RR comparing women in the highest quintile of plasma vitamin B(6 ) levels with those in the lowest quintile was 0.70 ( 95 % CI = 0.48 to 1.02 ; P(trend ) = .09 ) . Plasma vitamin B(12 ) levels were inversely associated with breast cancer risk among premenopausal women ( multivariable RR = 0.36 , 95 % CI = 0.15 to 0.86 for highest versus lowest quintile ) but not among postmenopausal women . Plasma homocysteine was not associated with breast cancer risk . CONCLUSIONS Higher plasma levels of folate and possibly vitamin B(6 ) may reduce the risk of developing breast cancer . Achieving adequate circulating levels of folate may be particularly important for women at higher risk of developing breast cancer because of higher alcohol consumption
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 .