Systematic Review of Observational Studies with Dose-Response Meta-Analysis between Folate Intake and Status Biomarkers in Adults and the Elderly.

BACKGROUND: Dietary reference values for folate intake vary widely across Europe. METHODS: MEDLINE and Embase through November 2016 were searched for data on the association between folate intake and biomarkers (serum/plasma folate, red blood cell [RBC] folate, plasma homocysteine) from observational studies in healthy adults and elderly. The regression coefficient of biomarkers on intake (ß) was extracted from each study, and the overall and stratified pooled ß and SE (ß) were obtained by random effects meta-analysis on a double log scale. These dose-response estimates may be used to derive folate intake reference values. RESULTS: For every doubling in folate intake, the changes in serum/plasma folate, RBC folate and plasma homocysteine were +22, +21, and -16% respectively. The overall pooled regression coefficients were ß = 0.29 (95% CI 0.21-0.37) for serum/plasma folate (26 estimates from 17 studies), ß = 0.28 (95% CI 0.21-0.36) for RBC (13 estimates from 11 studies), and ß = -0.21 (95% CI -0.31 to -0.11) for plasma homocysteine (10 estimates from 6 studies). CONCLUSION: These estimates along with those from randomized controlled trials can be used for underpinning dietary recommendations for folate in adults and elderly.

Vitamin B12 intake and status and cognitive function in elderly people.

Current recommendations on vitamin B12 intake vary from 1.4 to 3.0 µg per day and are based on the amount needed for maintenance of hematologic status or on the amount needed to compensate obligatory losses. This systematic review evaluates whether the relation between vitamin B12 intake and cognitive function should be considered for underpinning vitamin B12 recommendations in the future. The authors summarized dose-response evidence from randomized controlled trials and prospective cohort studies on the relation of vitamin B12 intake and status with cognitive function in adults and elderly people. Two randomized controlled trials and 6 cohort studies showed no association or inconsistent associations between vitamin B12 intake and cognitive function. Random-effects meta-analysis showed that serum/plasma vitamin B12 (50 pmol/L) was not associated with risk of dementia (4 cohort studies), global cognition z scores (4 cohort studies), or memory z scores (4 cohort studies). Although dose-response evidence on sensitive markers of vitamin B12 status (methylmalonic acid and holotranscobalamin) was scarce, 4 of 5 cohort studies reported significant associations with risk of dementia, Alzheimer's disease, or global cognition. Current evidence on the relation between vitamin B12 intake or status and cognitive function is not sufficient for consideration in the development of vitamin B12 recommendations. Further studies should consider the selection of sensitive markers of vitamin B12 status.

EURRECA-Estimating zinc requirements for deriving dietary reference values.

Zinc was selected as a priority micronutrient for EURRECA, because there is significant heterogeneity in the Dietary Reference Values (DRVs) across Europe. In addition, the prevalence of inadequate zinc intakes was thought to be high among all population groups worldwide, and the public health concern is considerable. In accordance with the EURRECA consortium principles and protocols, a series of literature reviews were undertaken in order to develop best practice guidelines for assessing dietary zinc intake and zinc status. These were incorporated into subsequent literature search strategies and protocols for studies investigating the relationships between zinc intake, status and health, as well as studies relating to the factorial approach (including bioavailability) for setting dietary recommendations. EMBASE (Ovid), Cochrane Library CENTRAL, and MEDLINE (Ovid) databases were searched for studies published up to February 2010 and collated into a series of Endnote databases that are available for the use of future DRV panels. Meta-analyses of data extracted from these publications were performed where possible in order to address specific questions relating to factors affecting dietary recommendations. This review has highlighted the need for more high quality studies to address gaps in current knowledge, in particular the continued search for a reliable biomarker of zinc status and the influence of genetic polymorphisms on individual dietary requirements. In addition, there is a need to further develop models of the effect of dietary inhibitors of zinc absorption and their impact on population dietary zinc requirements.

The relationship between zinc intake and serum/plasma zinc concentration in adults: a systematic review and dose-response meta-analysis by the EURRECA Network.

Dietary Zn recommendations vary widely across Europe due to the heterogeneity of approaches used by expert panels. Under the EURopean micronutrient RECommendations Aligned (EURRECA) consortium a protocol was designed to systematically review and undertake meta-analyses of research data to create a database that includes 'best practice' guidelines which can be used as a resource by future panels when setting micronutrient recommendations. As part of this process, the objective of the present study was to undertake a systematic review and meta-analysis of previously published data describing the relationship between Zn intake and status in adults. Searches were performed of literature published up to February 2010 using MEDLINE, Embase and the Cochrane Library. Data extracted included population characteristics, dose of Zn, duration of study, dietary intake of Zn, and mean concentration of Zn in plasma or serum at the end of the intervention period. An intake-status regression coefficient (ß ) was estimated for each individual study, and pooled meta-analysis undertaken. The overall pooled ß for Zn supplementation on serum/plasma Zn concentrations from randomised controlled trials and observational studies was 0·08 (95 % CI 0·05, 0·11; P < 0·0001; I² 84·5 %). An overall ß of 0·08 means that for every doubling in Zn intake, the difference in Zn serum or plasma concentration is ß (2(0·08) = 1·06), which is 6 %. Whether the dose-response relationship, as provided in the present paper, could be used as either qualitative or quantitative evidence to substantiate the daily Zn intake dose necessary to achieve normal or optimal levels of biomarkers for Zn status remains a matter of discussion.

Transformations of summary statistics as input in meta-analysis for linear dose-response models on a logarithmic scale: a methodology developed within EURRECA.

BACKGROUND: To derive micronutrient recommendations in a scientifically sound way, it is important to obtain and analyse all published information on the association between micronutrient intake and biochemical proxies for micronutrient status using a systematic approach. Therefore, it is important to incorporate information from randomized controlled trials as well as observational studies as both of these provide information on the association. However, original research papers present their data in various ways. METHODS: This paper presents a methodology to obtain an estimate of the dose-response curve, assuming a bivariate normal linear model on the logarithmic scale, incorporating a range of transformations of the original reported data. RESULTS: The simulation study, conducted to validate the methodology, shows that there is no bias in the transformations. Furthermore, it is shown that when the original studies report the mean and standard deviation or the geometric mean and confidence interval the results are less variable compared to when the median with IQR or range is reported in the original study. CONCLUSIONS: The presented methodology with transformations for various reported data provides a valid way to estimate the dose-response curve for micronutrient intake and status using both randomized controlled trials and observational studies.

Effect of folate intake on health outcomes in pregnancy: a systematic review and meta-analysis on birth weight, placental weight and length of gestation.

The beneficial effect of folic acid supplementation before and shortly after conception is well recognized, whereas the effect of supplementation during the second and third trimesters is controversial and poorly documented. Our aims were to systematically review randomized controlled trials (RCTs) investigating the effect of folate supplementation on birth weight, placental weight and length of gestation and to assess the dose-response relationship between folate intake (folic acid plus dietary folate) and health outcomes. The MEDLINE, EMBASE and Cochrane Library CENTRAL databases were searched from inception to February 2010 for RCTs in which folate intake and health outcomes in pregnancy were investigated. We calculated the overall intake-health regression coefficient (ß^) by using random-effects meta-analysis on a log(e)-log(e) scale. Data of 10 studies from 8 RCTs were analyzed. We found significant dose-response relationship between folate intake and birth weight (P=0.001), the overall ß^ was 0.03 (95% confidence interval (CI): 0.01, 0.05). This relationship indicated 2% increase in birth weight for every two-fold increase in folate intake. In contrast, we did not find any beneficial effect of folate supplementation on placental weight or on length of gestation. There is a paucity of well-conducted RCTs investigating the effect of folate supplementation on health outcomes in pregnancy. The dose-response methodology outlined in the present systematic review may be useful for designing clinical studies on folate supplementation and for developing recommendations for pregnant women.

Effect of fish oil on ventricular tachyarrhythmia in three studies in patients with implantable cardioverter defibrillators.

AIMS: To determine the effects of omega-3 polyunsaturated fatty acids (omega-3 PUFAs) from fish on the incidence of recurrent ventricular arrhythmia in implantable cardioverter defibrillator (ICD) patients by combining results from published trials. METHODS AND RESULTS: We searched in the Medline, EMBASE, and Cochrane databases and performed a meta-analysis on all three available trials on fish oil and ventricular arrhythmia. Furthermore, we pooled individual data of two of these randomized, double-blind, placebo-controlled trials (Raitt et al. Fish oil supplementation and risk of ventricular tachycardia and ventricular fibrillation in patients with implantable defibrillators: a randomized controlled trial. JAMA 2005;293:2884-2891 and Brouwer et al. Effect of fish oil on ventricular tachyarrhythmia and death in patients with implantable cardioverter defibrillators: the Study on Omega-3 Fatty Acids and Ventricular Arrhythmia (SOFA) randomized trial. JAMA 2006;295:2613-2619). The main outcome was time to first confirmed ventricular fibrillation (VF) or ventricular tachycardia (VT) combined with death for the meta-analysis, and time to first spontaneous confirmed VF or VT for the pooled analysis. The meta-analysis (n = 1148) showed no convincing protective effect of fish oil (RR 0.90; 95% CI 0.67-1.22). The hazard ratio for the subgroup of patients with coronary artery disease at baseline (0.79; 0.60-1.06) tended towards a protective effect. The pooled analysis (n = 722) showed that time to appropriate ICD intervention was similar for fish oil and placebo treatment (log-rank P = 0.79). CONCLUSION: These findings do not support a protective effect of omega-3 PUFAs from fish oil on cardiac arrhythmia in all patients with an ICD. Current data neither prove nor disprove a beneficial or a detrimental effect for subgroups of patients with specific underlying pathologies.

Differences in fatty acid composition between cerebral brain lobes in juvenile pigs after fish oil feeding.

Very long-chain n-3 PUFA from fish are suggested to play a role in the development of the brain. Fish oil feeding results in higher proportions of n-3 PUFA in the brains of newborn piglets. However, the effect of fish oil on the fatty acid composition of specific cerebral brain lobes in juvenile pigs is largely uninvestigated. This study examined the effect of a fish oil diet on the fatty acid composition of the frontal, parietal, temporal and occipital brain lobes in juvenile pigs (7 weeks old). Pigs were randomly allocated to a semipurified pig diet containing either 4% (w/w) fish oil (n 19) or 4% (w/w) high-oleic acid sunflower oil (HOSF diet, n 18) for a period of 8 weeks. The fish oil diet resulted in significantly higher proportions (%) of DHA in the frontal (10.6 (SD1.2)), parietal (10.2 (SD1.5)) and occipital brain lobes (9.9 (SD 1.3)), but not in the temporal lobe (7.7 (SD1.6)), compared with pigs fed the HOSF diet (frontal lobe, 7.5 (SD1.0); parietal lobe, 8.1 (SD 1.3); occipital lobe, 7.3 (SD1.2), temporal lobe, 6.6 (SD1.2). Moreover, the proportion of DHA was significantly lower in the temporal lobe compared with the frontal, parietal and occipital brain lobes in pigs fed a fish oil diet. In conclusion, the brains of juvenile pigs appear to be responsive to dietary fish oil, although the temporal brain lobe is less responsive compared with the other three brain lobes. The functional consequences of these differences are a challenging focus for future investigation.

n 3 fatty acid proportions in plasma and cognitive performance in older adults.

BACKGROUND: Very-long-chain n-3 polyunsaturated fatty acids (n-3 PUFAs) are suggested to be related to cognitive performance in older adults. However, limited data exist on the association between n-3 PUFAs and performance in specific cognitive domains. OBJECTIVE: We evaluated the association between plasma n-3 PUFA proportions and cognitive performance in 5 cognitive domains and determined whether plasma n-3 PUFA proportions predict cognitive change over 3 y. DESIGN: We used data from the FACIT trial, in which participants received folic acid or placebo capsules for 3 y. Fatty acid proportions in plasma cholesteryl esters at baseline were measured in 807 men and women aged 50-70 y. Cognitive performance for memory, sensorimotor speed, complex speed, information-processing speed, and word fluency was assessed at baseline and after 3 y. The cross-sectional analyses were based on all 807 participants; the longitudinal analyses were based only on 404 participants in the placebo group. RESULTS: Higher plasma n-3 PUFA proportions predicted less decline in sensorimotor speed (multiple linear regression coefficient, z score = 0.31; 95% CI: 0.06, 0.57) and complex speed (0.40; 95% CI: 0.10, 0.70) over 3 y. Plasma n-3 PUFA proportions did not predict 3-y changes in memory, information-processing speed, or word fluency. The cross-sectional analyses showed no association between plasma n-3 PUFA proportions and performance in any of the 5 cognitive domains. CONCLUSIONS: In this population, plasma n-3 PUFA proportions were associated with less decline in the speed-related cognitive domains over 3 y. These results need to be confirmed in randomized controlled trials.

Effect of fish oil on ventricular tachyarrhythmia and death in patients with implantable cardioverter defibrillators: the Study on Omega-3 Fatty Acids and Ventricular Arrhythmia (SOFA) randomized trial.

CONTEXT: Very-long-chain n-3 polyunsaturated fatty acids (omega-3 PUFAs) from fish are thought to reduce risk of sudden death, possibly by reducing susceptibility to cardiac arrhythmia. OBJECTIVE: To study the effect of supplemental fish oil vs placebo on ventricular tachyarrhythmia or death. DESIGN, SETTING, AND PATIENTS: The Study on Omega-3 Fatty acids and ventricular Arrhythmia (SOFA) was a randomized, parallel, placebo-controlled, double-blind trial conducted at 26 cardiology clinics across Europe. A total of 546 patients with implantable cardioverter-defibrillators (ICDs) and prior documented malignant ventricular tachycardia (VT) or ventricular fibrillation (VF) were enrolled between October 2001 and August 2004. Patients were randomly assigned to receive 2 g/d of fish oil (n = 273) or placebo (n = 273) for a median period of 356 days (range, 14-379 days). MAIN OUTCOME MEASURE: Appropriate ICD intervention for VT or VF, or all-cause death. RESULTS: The primary end point occurred in 81 (30%) patients taking fish oil vs 90 (33%) patients taking placebo (hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.64-1.16; P = .33). In prespecified subgroup analyses, the HR was 0.91 (95% CI, 0.66-1.26) for fish oil vs placebo in the 411 patients who had experienced VT in the year before the study, and 0.76 (95% CI, 0.52-1.11) for 332 patients with prior myocardial infarctions. CONCLUSION: Our findings do not indicate evidence of a strong protective effect of intake of omega-3 PUFAs from fish oil against ventricular arrhythmia in patients with ICDs. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00110838.

Biomarker responses to folic acid intervention in healthy adults: a meta-analysis of randomized controlled trials.

BACKGROUND: The task of revising dietary folate recommendations for optimal health is complicated by a lack of data quantifying the biomarker response that reliably reflects a given folate intake. OBJECTIVE: We conducted a dose-response meta-analysis in healthy adults to quantify the typical response of recognized folate biomarkers to a change in folic acid intake. DESIGN: Electronic and bibliographic searches identified 19 randomized controlled trials that supplemented with folic acid and measured folate biomarkers before and after the intervention in apparently healthy adults aged ≥18 y. For each biomarker response, the regression coefficient (ß) for individual studies and the overall pooled ß were calculated by using random-effects meta-analysis. RESULTS: Folate biomarkers (serum/plasma and red blood cell folate) increased in response to folic acid in a dose-response manner only up to an intake of 400 µg/d. Calculation of the overall pooled ß for studies in the range of 50 to 400 µg/d indicated that a doubling of folic acid intake resulted in an increase in serum/plasma folate by 63% (71% for microbiological assay; 61% for nonmicrobiological assay) and red blood cell folate by 31% (irrespective of whether microbiological or other assay was used). Studies that used the microbiological assay indicated lower heterogeneity compared with studies using nonmicrobiological assays for determining serum/plasma (I(2) = 13.5% compared with I(2) = 77.2%) and red blood cell (I(2) = 45.9% compared with I(2) = 70.2%) folate. CONCLUSIONS: Studies administering >400 µg folic acid/d show no dose-response relation and thus will not yield meaningful results for consideration when generating dietary folate recommendations. The calculated folate biomarker response to a given folic acid intake may be more robust with the use of a microbiological assay rather than alternative methods for blood folate measurement.

Systematic review using meta-analyses to estimate dose-response relationships between iodine intake and biomarkers of iodine status in different population groups.

The objective of this systematic review was to identify studies investigating iodine intake and biomarkers of iodine status, to assess the data of the selected studies, and to estimate dose-response relationships using meta-analysis. All randomized controlled trials, prospective cohort studies, nested case-control studies, and cross-sectional studies that supplied or measured dietary iodine and measured iodine biomarkers were included. The overall pooled regression coefficient (ß) and the standard error of ß were calculated by random-effects meta-analysis on a double-log scale, using the calculated intake-status regression coefficient (ß) for each individual study. The results of pooled randomized controlled trials indicated that the doubling of dietary iodine intake increased urinary iodine concentrations by 14% in children and adolescents, by 57% in adults and the elderly, and by 81% in pregnant women. The dose-response relationship between iodine intake and biomarkers of iodine status indicated a 12% decrease in thyroid-stimulating hormone and a 31% decrease in thyroglobulin in pregnant women. The model of dose-response quantification used to describe the relationship between iodine intake and biomarkers of iodine status may be useful for providing complementary evidence to support recommendations for iodine intake in different population groups.

Systematic review with dose-response meta-analyses between vitamin B-12 intake and European Micronutrient Recommendations Aligned's prioritized biomarkers of vitamin B-12 including randomized controlled trials and observational studies in adults and elderly persons.

BACKGROUND: Many randomized 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 systematically reviewed 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. DESIGN: This systematic review included all RCTs, prospective cohort studies, nested case-control studies, and cross-sectional studies in healthy adult populations published through January 2010 that supplied or measured dietary vitamin B-12 intake and measured vitamin B-12 status as serum or plasma vitamin B-12, methylmalonic acid (MMA), or holotranscobalamin. We calculated an intake-status regression coefficient ( ) for each individual study and calculated the overall pooled and SE ( ) by using random-effects meta-analysis on a double-log scale. RESULTS: The meta-analysis of observational studies showed a weaker slope of dose-response relations than the meta-analysis of RCTs. The pooled dose-response relation of all studies between vitamin B-12 intake and status indicated that a doubling of the vitamin B-12 intake increased vitamin B-12 concentrations by 11% (95% CI: 9.4%, 12.5%). This increase was larger for studies in elderly persons (13%) than in studies in adults (8%). The dose-response relation between vitamin B-12 intake and MMA concentrations indicated a decrease in MMA of 7% (95% CI: -10%, -4%) for every doubling of the vitamin B-12 intake. The assessment of risk of bias within individual studies and across studies indicated risk that was unlikely to seriously alter these results. CONCLUSION: 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 populations.

The relationship between zinc intake and serum/plasma zinc concentration in pregnant and lactating women: a systematic review with dose-response meta-analyses.

Recommendations for zinc intake during pregnancy and lactation vary widely across Europe. Using data on zinc intake and biomarkers of zinc status reported in randomized controlled trials (RCTs) and observational studies can provide estimates of dose-response relationships that may be used for underpinning zinc reference values. This systematic review included all RCTs, prospective cohort studies, nested case-control studies and cross-sectional studies in healthy pregnant and lactating populations published by February 2010 which provided data on zinc intake and biomarkers of zinc status. An intake-status regression coefficient (߈) was calculated for each individual study and calculated the overall pooled ߈ and SE (߈) using random effects meta-analysis on a double log scale. The pooled dose-response relationship between zinc intake and zinc status found that a doubling of zinc intake was associated with an increase in serum/plasma zinc status by 3% in pregnant women and by 1% in lactating women. These modest associations are likely to reflect the low-moderate zinc bioavailability dietary patterns and the widespread use of other micronutrients in the populations included in this review, physiologic adjustments of zinc homeostasis, insensitivity of serum/plasma zinc as a biomarker of zinc status, and wide heterogeneity between study results which reflect real uncertainty in the current evidence base. Although this review provides useful information for dietary zinc requirements in populations vulnerable to zinc deficiency, it also highlights a need for further studies in pregnant and lactating women with different dietary patterns in order to provide useful complementary evidence that can be utilized when setting zinc recommendations as a basis for nutrition policies in Europe.

The relationship between zinc intake and serum/plasma zinc concentration in children: a systematic review and dose-response meta-analysis.

Recommendations for zinc intake during childhood vary widely across Europe. The EURRECA project attempts to consolidate the basis for the definition of micronutrient requirements, taking into account relationships among intake, status and health outcomes, in order to harmonise these recommendations. Data on zinc intake and biomarkers of zinc status reported in randomised controlled trials (RCTs) can provide estimates of dose-response relationships which may be used for underpinning zinc reference values. This systematic review included all RCTs of apparently healthy children aged 1-17 years published by February 2010 which provided data on zinc intake and biomarkers of zinc status. An intake-status regression coefficient (ß) was calculated for each individual study and calculated the overall pooled and SE (ß) using random effects meta-analysis on a double log scale. The pooled dose-response relationship between zinc intake and zinc status indicated that a doubling of the zinc intake increased the serum/plasma zinc status by 9%. This evidence can be utilised, together with currently used balance studies and repletion/depletion studies, when setting zinc recommendations as a basis for nutrition policies.

Folate intake and markers of folate status in women of reproductive age, pregnant and lactating women: a meta-analysis.

Background. Pregnant and breastfeeding women are at risk for folate deficiency. Folate supplementation has been shown to be associated with enhanced markers of folate status. However, dose-response analyses for adult women are still lacking. Objective. To assess the dose-response relationship between total folate intake (folic acid plus dietary folate) and markers of folate status (plasma/serum folate, red blood cell folate, and plasma homocysteine); to evaluate potential differences between women in childbearing age, pregnant and lactating women. Methods. Electronic literature searches were carried out on three databases until February 2010. The overall pooled regression coefficient (ß) and SE(ß) were calculated using meta-analysis on a double-log scale. Results. The majority of data was based on nonpregnant, nonlactating women in childbearingage. The pooled estimate of the relationship between folate intake and serum/plasma folate was 0.56 (95% CI = 0.40-0.72, P < 0.00001); that is, the doubling of folate intake increases the folate level in serum/plasma by 47%. For red blood cell folate, the pooled-effect estimate was 0.30 (95% CI = 0.22-0.38, P < 0.00001), that is, +23% for doubling intake. For plasma-homocysteine it was -0.10 (95% = -0.17 to -0.04, P = 0.001), that is, -7% for doubling the intake. Associations tended to be weaker in pregnant and lactating women. Conclusion. Significant relationships between folate intake and serum/plasma folate, red blood cell folate, and plasma homocysteine were quantified. This dose-response methodology may be applied for setting requirements for women in childbearing age, as well as for pregnant and lactating women.