***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Animal source foods ( ASF ) can provide micronutrients in greater amounts and more bioavailable forms compared to plant source foods , but their intake is low in many poor population s. However , the impact of ASF on micronutrient status of undernourished population s has not been assessed . Supplemental meat ( 60 - 85 g/d ) , milk ( 200 - 250 mL/d ) or energy ( isocaloric with the meat and milk , 240 - 300 kcal/d ) were r and omly assigned to 555 undernourished school children aged 5 - 14 y in a rural malaria-endemic area of Kenya , at one school meal daily for one school year . Blood and stool sample s were collected at baseline and after 1 y to assess stool parasites , malaria , hemoglobin , serum or plasma C-reactive protein , ferritin , iron , zinc , copper , vitamin B-12 , folate and retinol , and erythrocyte riboflavin . At baseline , there was a high prevalence of micronutrient deficiencies ( iron , zinc , vitamins A and B-12 and riboflavin ) , yet plasma ferritin was low in few children , and none had low serum copper . At the end of the year of supplementation , plasma vitamin B-12 concentrations were significantly increased in children fed the Meat or Milk meal ; prevalence of severe plus moderate deficiency fell from 80.7 % at baseline to 64.1 % in the Meat group and from 71.6 to 45.1 % in the Milk group , respectively . No significant improvement was observed in the status of other micronutrients compared to the Energy and Control groups , although malaria and other infections may have obscured effects . Supplementation with small amounts of meat or milk reduced the high prevalence of vitamin B-12 deficiency in these children Sixty rural Gambian children between 10 and 14 years of age with normal haematological status but generally poor riboflavin status and some evidence of poor ascorbic acid status were recruited for study at the beginning of the rainy season . Children were allocated to three treatment groups to receive , twice weekly , either a placebo or a supplement of riboflavin or ascorbic acid . Before receiving the supplement , and on two subsequent occasions 6 weeks apart children performed an exercise regimen on a bicycle ergometer during which expired air was collected , heart rate monitored and lactate accumulation measured . A modest but significant improvement in ascorbic acid status occurred in response to supplement and the riboflavin supplement enhanced the overall improvement in riboflavin status observed . There was no measurable change in bicycling performance during the study period in any of the treatment groups The effects of pyridoxine and riboflavin supplementation on physical fitness was studied in a group of children with higher prevalence of sub clinical , biochemically defined pyridoxine and riboflavin deficiencies . One hundred and thirteen children aged 12 - 14 years were allocated to three groups to receive daily ( except Sundays ) for two months either a placebo or a supplement of pyridoxine or riboflavin . The supplementation result ed in marked improvement of pyridoxine and riboflavin nutrition status and was followed by disappearance of respective biochemical deficiencies . The improvement in pyridoxine biochemical status was also accompanied by a slight and statistically significant increase in physical fitness ( p less than 0.05 ) assessed by bicycle ergometer technique . The increase in physical fitness in the riboflavin supplemented group was statistically non-significant ( p greater than 0.05 ) . In both supplemented groups there was a significant increase in physical fitness in subjects with initially deficient biochemical vitamin status whereas supplementation had no effect on physical fitness in subjects with initially high biochemical values Free-living elderly people aged > or = 65 y were recruited to assess riboflavin and vitamin B-6 intakes and status and the effect of riboflavin supplementation on biochemical indicators of these 2 vitamins . The status of riboflavin ( erythrocyte glutathione reductase activation coefficient ; EGRAC ) and  vitamin B-6 ( plasma pyridoxal-5'-phosphate ; PLP ) were determined in a total sample of 92 subjects , from whom dietary intake data were obtained by using the diet history method ( n = 83 ) . Although dietary intakes of both vitamins were considered to be adequate according to current reference values , abnormal EGRAC and plasma PLP values were identified in 49 % and 38 % of subjects , respectively , with 21 % having suboptimal status for both nutrients . A subgroup of subjects from the initial sample ( n = 45 ) was assigned in a double-blind manner to receive either 1.6 or 25 mg riboflavin or placebo daily for 12 wk . In those subjects with a baseline EGRAC or plasma PLP value falling outside the currently accepted threshold value for adequacy , low-dose riboflavin supplementation improved status of the limiting nutrient significantly ( P<0.0001 and P = 0.020 for EGRAC and plasma PLP responses , respectively ) . We conclude that a high proportion of healthy elderly people may have suboptimal status for these nutrients despite apparently adequate dietary intakes . Furthermore , we showed that riboflavin supplementation at physiologic doses corrects biochemical abnormalities of not only EGRAC , but also plasma PLP , confirming the biochemical interdependency of these vitamins and suggesting that riboflavin is the limiting nutrient As part of a study to determine the minimum allowance of riboflavin which is adequate for lactating women in a rural African environment , 60 subjects living in two Gambian villages were given either 2 mg riboflavin or a placebo daily on a double-blind basis for 12 wk . Their riboflavin intake from dietary sources was about 0.5 mg/day . In the supplemented group , the mean activation coefficient ( AC ) of erythrocyte glutathione reductase fell from 1.62 to 1.19 within 3 wk , and 90 % had mean AC 's below 1.3 throughout supplementation , whereas the placebo group maintained mean AC 's between 1.6 and 1.9 . Clinical signs associated with riboflavin deficiency improved more rapidly in the supplemented group ; their breast milk riboflavin levels increased , and their infants ' AC 's were reduced , compared with those of the placebo group . After withdrawal of the supplement , the maternal and infants ' AC 's rose toward those of the placebo group . Thus a total riboflavin intake of about 2.5 mg/day during lactation is sufficient to maintain normal biochemical status in most Gambian women BACKGROUND Methylenetetrahydrofolate reductase ( MTHFR ; EC 1.7.99.5 ) supplies the folate needed for the metabolism of homocysteine . A reduction in MTHFR activity , as occurs in the homozygous state for the 677C-->T ( so-called thermolabile ) enzyme variant ( TT genotype ) , is associated with an increase in plasma total homocysteine ( tHcy ) . OBJECTIVE In vitro studies suggest that the reduced activity of thermolabile MTHFR is due to the inappropriate loss of its riboflavin cofactor . We investigated the hypothesis that MTHFR activity in the TT genotype group is particularly sensitive to riboflavin status . DESIGN We studied tHcy and relevant B-vitamin status by MTHFR genotype in a cross-sectional study of 286 healthy subjects aged 19 - 63 y ( median : 27 y ) . The effect of riboflavin status was examined by dividing the sample into tertiles of erythrocyte glutathionine reductase activation coefficient , a functional index of riboflavin status . RESULTS Lower red blood cell folate ( P = 0.0001 ) and higher tHcy ( P = 0.0082 ) concentrations were found in the TT group than in the heterozygous ( CT ) or wild-type ( CC ) groups . However , these expected relations in the total sample were driven by the TT group with the lowest riboflavin status , whose mean tHcy concentration ( 18.09 micromol/L ) was almost twice that of the CC or CT group . By contrast , adequate riboflavin status rendered the TT group neutral with respect to tHcy metabolism . CONCLUSIONS The high tHcy concentration typically associated with homozygosity for the 677C-->T variant of MTHFR occurs only with poor riboflavin status . This may have important implication s for governments considering new fortification policies aim ed at the prevention of diseases for which this genotype is associated with increased risk The pharmacokinetics and utilization ( flavocoenzyme synthesis ) of orally and intravenously administered riboflavin in healthy humans were assessed . After the determination of circadian rhythms of riboflavin concentrations in blood plasma and urine of four males and five females ( control period ) , each of these subjects received three different oral riboflavin doses ( 20 , 40 , and 60 mg ) and one intravenous bolus injection of riboflavin ( 11.6 mg ) . Vitamins were administered in a r and omized , cross-over design with 2 wk between each administration . Blood plasma and urine specimens were collected repeatedly over a period of 48 h after each administration . Concentrations of flavocoenzymes and riboflavin were analyzed in blood plasma ; riboflavin was assayed in urine . During the control period , a small circadian variation was observed : plasma concentrations and urinary excretion of riboflavin were low during the afternoon ( P < 0.05 ) . Pharmacokinetics were calculated using a two-compartment open model . The maximal amount of riboflavin that can be absorbed from a single dose was 27 mg per adult . Half-life of absorption was 1.1 h. First-order rate constants describing distribution and elimination of riboflavin were significantly higher after intravenous than after oral administration ( P < 0.01 ) . Release of flavocoenzymes into plasma was low compared with the increase of riboflavin concentrations . 7 alpha-Hydroxyriboflavin was identified in plasma . Clearance data indicated that urinary excretion of riboflavin contributes to one-half of the overall removal of riboflavin from plasma . No sex differences were observed for any of the pharmacokinetic variables ( P > 0.05 ) BACKGROUND Vitamin B(2 ) exists in blood as riboflavin and its cofactors , flavin mononucleotide ( FMN ) and FAD . The erythrocyte glutathione reductase activation coefficient ( EGRAC ) has traditionally been used to assess vitamin B(2 ) status in humans . We investigated the relationships of EGRAC and plasma and erythrocyte concentrations of riboflavin , FMN , and FAD in elderly volunteers and their responses to riboflavin administration . METHODS EGRAC and plasma and erythrocyte concentrations of riboflavin , FMN , and FAD were determined in 124 healthy individuals with a mean age of 69 years . The same measurements were made in a subgroup of 46 individuals with EGRAC > or = 1.20 who participated in a r and omized double-blind 12-week intervention study and received riboflavin ( 1.6 mg/day ; n = 23 ) or placebo ( n = 23 ) . RESULTS Median plasma concentrations were 10.5 nmol/L for riboflavin , 6.6 nmol/L for FMN , and 74 nmol/L for FAD . In erythrocytes , there were only trace amounts of riboflavin , whereas median FMN and FAD concentrations were 44 and 469 nmol/L , respectively . Erythrocyte FMN and FAD correlated with each other and with EGRAC and plasma riboflavin ( P < 0.05 ) . All variables except plasma FAD responded significantly to riboflavin supplementation compared with placebo ( P < or = 0.04 ) . The strongest increases were for riboflavin in plasma ( 83 % ) and for FMN in erythrocytes ( 87 % ) . CONCLUSIONS Concentrations of all B(2 ) vitamers except plasma FAD are potential indicators of vitamin B(2 ) status , and plasma riboflavin and erythrocyte FMN may be useful for the assessment of vitamin B(2 ) status in population studies Eighty-one pregnant or lactating women living in a village in The Gambia were allocated to treatment groups to receive a daily placebo , riboflavin , ferrous sulphate or ferrous sulphate plus riboflavin . At the beginning of the study and at 3 and 6 weeks thereafter women were examined clinical ly and blood sample s collected for haematological and biochemical measurements . Pregnant women showed a wide range of response to supplement but among the lactating women an interesting pattern emerged : whereas the haematological status of the placebo group declined over 6 weeks , in the group receiving iron supplements this deterioration was reduced although not significantly . Riboflavin given in addition to iron result ed in a significant increase in circulating plasma iron and in iron stores , relative to the placebo BACKGROUND Meta-analyses predict that a 25 % lowering of plasma homocysteine would reduce the risk of coronary heart disease by 11 % to 16 % and stroke by 19 % to 24 % . Individuals homozygous for the methylenetetrahydrofolate reductase ( MTHFR ) 677C-->T polymorphism have reduced M 
    Output:
    
Plasma total homocysteine was not an effective biomarker of riboflavin status in the general population , but some evidence identified its potential usefulness specifically in those homozygous for a common polymorphism in the MTHFR gene .
The evidence suggests that EGRac is an effective biomarker of a change in riboflavin intake in population s with severe-to-normal baseline status .