BACKGROUND: Multiple systematic reviews examine the introduction of foods in relation to individual health outcomes, but the balance of harms and benefits has not been overviewed systematically.
OBJECTIVES: We aimed to perform an overview of systematic reviews on age of introduction of complementary and allergenic foods to the infant diet and long and short-term health outcomes.
DATA SOURCES: We searched Medline, Embase, Cochrane, and PubMed (July 25, 2022).
STUDY SELECTION: Included systematic reviews examining the introduction of complementary or allergenic foods before age 1. Outcomes included allergic, autoimmune, and inflammatory diseases, neurodevelopment, nutrition, and weight.
DATA EXTRACTION: Extraction and quality assessment were performed in duplicate (A Measurement Tool to Assess Systematic Reviews) and strength of evidence was assessed.
RESULTS: We screened 4015 articles and included 32 systematic reviews. There was moderate evidence that peanut and egg should be introduced from 4 to 11 months to prevent food allergy (6 of 10 reviews). Complementary food introduction was not associated with food allergy. Moderate certainty evidence suggested age of complementary food introduction was not associated with eczema. Age at introduction of gluten was not associated with celiac disease (high certainty evidence; 3 of 4 reviews). Low certainty evidence indicated that introducing solids before 4 months may increase the risk of childhood obesity, but not growth. There was insufficient evidence regarding an association between any food introduction and bone health, gastrointestinal diseases, autoimmune disorders, asthma, or allergic rhinitis.
LIMITATIONS: Gray literature was not included.
CONCLUSIONS: Current evidence supports introducing complementary foods around 6 months and allergenic foods before 11 months.
BACKGROUND: COPD and adult-onset asthma (AOA) are the most common noncommunicable respiratory diseases. To improve early identification and prevention, an overview of risk factors is needed. We therefore aimed to systematically summarise the nongenetic (exposome) risk factors for AOA and COPD. Additionally, we aimed to compare the risk factors for COPD and AOA.
METHODS: In this umbrella review, we searched PubMed for articles from inception until 1 February 2023 and screened the references of relevant articles. We included systematic reviews and meta-analyses of observational epidemiological studies in humans that assessed a minimum of one lifestyle or environmental risk factor for AOA or COPD.
RESULTS: In total, 75 reviews were included, of which 45 focused on risk factors for COPD, 28 on AOA and two examined both. For asthma, 43 different risk factors were identified while 45 were identified for COPD. For AOA, smoking, a high body mass index (BMI), wood dust exposure and residential chemical exposures, such as formaldehyde exposure or exposure to volatile organic compounds, were amongst the risk factors found. For COPD, smoking, ambient air pollution including nitrogen dioxide, a low BMI, indoor biomass burning, childhood asthma, occupational dust exposure and diet were amongst the risk factors found.
CONCLUSIONS: Many different factors for COPD and asthma have been found, highlighting the differences and similarities. The results of this systematic review can be used to target and identify people at high risk for COPD or AOA.
BACKGROUND & OBJECTIVE: It has been suggested that prenatal vitamin D plays a role in the development of childhood asthma and wheeze. Several systematic reviews have been conducted, but the results are inconsistent, and the methodological quality has not been studied. Therefore, the objective of this umbrella review was to assess the internal validity of the evidence base and the evidence for an association between prenatal vitamin D and asthma or wheezing in the offspring.
METHODS: We searched the electronic databases Embase, PubMed, and Cochrane Library for studies on prenatal vitamin D using search words such as vitamin D, 25-hydroxyvitamin D, calcidiol, fetal, and neonatal. The search was conducted in June 2020, and the databases were searched from their date of establishment. We included systematic reviews and/or meta-analyses of experimental and observational studies assessing the association between prenatal vitamin D or asthma and wheeze. We excluded narrative reviews, commentaries, and other umbrella reviews. The methodological quality of systematic reviews was assessed using AMSTAR 2 tool. PROSPERO reg. no. CRD42020151329.
RESULTS: We identified 22 eligible systematic reviews (17 on asthma and 20 on wheeze). Using the AMSTAR 2 quality assessment tool, the methodological quality was rated as critically low in 21 out of 22 systematic reviews, suggesting that previous reviews and meta-analyses did not provide accurate and comprehensive summaries of the included studies and that conclusions reached were potentially flawed. The majority of the included reviews reported that prenatal vitamin D reduces the risk of wheeze in the offspring.
CONCLUSION: Prior to informing public guidelines, high-quality systematic reviews of the current evidence are greatly warranted.
Diet, physical activity, smoking and alcohol behaviour-change interventions delivered in pregnancy aim to prevent adverse pregnancy outcomes. This review reports a synthesis of evidence from meta-analyses on the effectiveness of interventions at reducing risk of adverse health outcomes. Sixty-five systematic reviews (63 diet and physical activity; 2 smoking) reporting 602 meta-analyses, published since 2011, were identified; no data were identified for alcohol interventions. A wide range of outcomes were reported, including gestational weight gain, hypertensive disorders, gestational diabetes (GDM) and fetal growth. There was consistent evidence from diet and physical activity interventions for a significantly reduced mean gestational weight gain (ranging from -0.21 kg (95% confidence interval -0.34, -0.08) to -5.77 kg (95% CI -9.34, -2.21). There was evidence from larger diet and physical activity meta-analyses for a significant reduction in postnatal weight retention, caesarean delivery, preeclampsia, hypertension, GDM and preterm delivery, and for smoking interventions to significantly increase birth weight. There was no statistically significant evidence of interventions having an effect on low or high birthweight, neonatal intensive care unit admission, Apgar score or mortality outcomes. Priority areas for future research to capitalise on pregnancy as an opportunity to improve the lifelong wellbeing of women and their children are highlighted.
PURPOSE: To assess the benefits and harms of folic acid supplementation in reproductive-age women for the prevention of neural tube defects (NTDs).
DATA SOURCES: Systematic review of studies from MEDLINE, the Cochrane Library, EMBASE unpublished literature, and trial registries through January 28, 2016; bibliographies from retrieved articles, outside experts, and reviewers.
STUDY SELECTION: Two investigators independently selected studies using a priori inclusion and exclusion criteria. We included studies that focused on the use of folic acid supplementation (by itself or in multivitamin or prenatal supplement form) for the prevention of NTD-affected pregnancies in women of childbearing age. We limited the evaluation of benefits to NTDs. We excluded poor-quality studies and studies of prepubertal girls, men or women without the potential for childbearing, and NTD recurrence prevention, and studies in developing countries.
DATA EXTRACTION: One investigator extracted data and a second checked accuracy. Two reviewers independently rated the quality for all included studies, using predefined criteria.
DATA SYNTHESIS: We included 24 studies: 12 on the effect of folic acid supplementation on NTDs, three on variation in the effect on NTDs by race/ethnicity, and eight on variation by dosage or timing. For harms, we focused on two recent systematic reviews on respiratory outcomes, which reported on several included studies. One systematic review also provided data on variation in harms by timing and dose. We paid particular attention in the analysis to variation in effect by study design and over time, particularly before and after food fortification in the United States (1998). For the question of benefits of folic acid supplementation on NTDs, we found a single randomized, controlled trial (RCT), initiated in 1984 in Hungary, reporting a Peto odds ratio (OR) for NTDs of 0.131 (95% confidence interval [CI], 0.026 to 0.648; p=0.013). Two older cohort studies provided an OR of 0.11 (95% CI, 0.011 to 0.91) and 0.27 (95% CI, 0.11 to 0.63). Older case-control studies were also generally consistent with the evidence from the older RCT and cohort studies; odds ranged from 0.6 to 0.7 in three of four case-control studies. This evidence led to food fortification in the United States in 1998, after which no new trials or prospective cohort studies have been conducted. All newer evidence arises from case-control studies only. These newer studies, with inherently weaker designs, are consistent in not demonstrating a protective effect of folic acid supplements on NTDs, with odds ranging from 0.9 to 1.4 and CIs spanning the null. Regarding variations in benefits by race/ethnicity, we found three eligible studies. One found no effect by race/ethnicity, a second found a higher but nonsignificant risk of NTDs with folic acid supplementation among Hispanic women (adjusted OR for consistent users compared with nonusers, 2.20 [95% CI, 0.98 to 4.92]), and a third found that the risk reduction was of smaller magnitude for Hispanic women compared with white or black women. These inconsistent results could have occurred by chance. Regarding variation in benefits, eight studies provided information. Of these, four studies provided information on dose, none on duration, and five on timing. We found no indication of a dose-response relationship in three of four studies. One study showed lower odds for daily versus less than daily use (OR, 0.57 [95% CI, 0.35 to 0.93]). Regarding timing, two older studies consistently showed no effect. Two newer studies found no effect of timing for spina bifida, while one showed a protective effect with supplement use before pregnancy for anencephaly. Regarding harms, one trial and one cohort study did not find evidence of statistically significant increased risk of twinning in women. The cohort study found that any increased risk of twinning was attenuated when the confounding effects of in vitro fertilization were accounted for. Three systematic reviews evaluated childhood asthma, wheezing, or allergy and found no consistent evidence of harm. One trial evaluated the risks of adverse events in women and found a higher risk of some events (weight gain, diarrhea, constipation) and not others (increased appetite, lack of appetite, exanthema, heartburn, and vertigo), but the event rate was very low and could have occurred by chance or as consequence of pregnancy. One systematic review did not find consistent evidence of an effect of folic acid supplementation on childhood asthma, wheezing, and allergy by timing or dose of intake.
LIMITATIONS: We restricted interventions to folic acid supplementation and did not include interventions such as food fortification, counseling to increase dietary intake, or screening for NTDs. We found very limited information on differences in benefits and risks of folic acid supplementation by race/ethnicity, dose, and timing and no information on duration. Regarding the overall quality of evidence, ethical considerations limit the use of RCTs to answer questions of efficacy. Observational studies carry limitations of case ascertainment and recall bias, and these two sources of bias can serve to reduce the observed effect of NTDs.
CONCLUSIONS: Studies conducted before food fortification in the United States in 1998, with fewer design flaws, show that folic acid supplementation provides protection against NTDs. Newer studies, conducted after food fortification with folic acid, do not demonstrate this protective effect. These studies, however, have the potential for misclassification and recall bias, both of which can serve to attenuate the effect of folic acid supplementation on NTDs. Although mandatory food fortification in the United States has been accompanied by a decline in NTD prevalence, variations in intake continue to leave nearly a quarter of the U.S. population with suboptimal red blood cell folate concentrations, suggesting continued importance of folic acid supplement use. Evidence of variations in effectiveness by race/ethnicity is inconsistent and could have occurred due to chance. We found no evidence of a dose-response effect, but studies had small numbers of cases for subanalyses. We did not find consistent evidence on timing of folic acid for benefits. We also did not find consistent evidence of harms, specifically twinning, respiratory outcomes, and other harms.
Multiple systematic reviews examine the introduction of foods in relation to individual health outcomes, but the balance of harms and benefits has not been overviewed systematically.
OBJECTIVES:
We aimed to perform an overview of systematic reviews on age of introduction of complementary and allergenic foods to the infant diet and long and short-term health outcomes.
DATA SOURCES:
We searched Medline, Embase, Cochrane, and PubMed (July 25, 2022).
STUDY SELECTION:
Included systematic reviews examining the introduction of complementary or allergenic foods before age 1. Outcomes included allergic, autoimmune, and inflammatory diseases, neurodevelopment, nutrition, and weight.
DATA EXTRACTION:
Extraction and quality assessment were performed in duplicate (A Measurement Tool to Assess Systematic Reviews) and strength of evidence was assessed.
RESULTS:
We screened 4015 articles and included 32 systematic reviews. There was moderate evidence that peanut and egg should be introduced from 4 to 11 months to prevent food allergy (6 of 10 reviews). Complementary food introduction was not associated with food allergy. Moderate certainty evidence suggested age of complementary food introduction was not associated with eczema. Age at introduction of gluten was not associated with celiac disease (high certainty evidence; 3 of 4 reviews). Low certainty evidence indicated that introducing solids before 4 months may increase the risk of childhood obesity, but not growth. There was insufficient evidence regarding an association between any food introduction and bone health, gastrointestinal diseases, autoimmune disorders, asthma, or allergic rhinitis.
LIMITATIONS:
Gray literature was not included.
CONCLUSIONS:
Current evidence supports introducing complementary foods around 6 months and allergenic foods before 11 months.
