Randomized trials and public health interventions: time to end the scientific double standard

Developmental Origins of Disease: Emerging Prenatal Risk Factors and Future Disease Risk

Purpose of review

Many of the diseases and dysfunctions described in the paradigm of the developmental origins of health and disease have been studied in relation to prenatal nutrition or environmental toxicant exposures. Here, we selectively review the current research on four exposures-two nutritional and two environmental-that have recently emerged as prenatal risk factors for long-term health outcomes.

Recent findings

Recent studies have provided strong evidence that prenatal exposure to (1) excessive intake of sugar-sweetened beverages, (2) unhealthy dietary patterns, (3) perfluoroalkyl substances, and (4) fine particulate matter, may increase risk of adverse health outcomes, such as obesity, cardiometabolic dysfunction, and allergy/asthma.

Summary

Emerging prenatal nutritional factors and environmental toxicants influence offspring long-term health. More work is needed to identify the role of paternal exposures and maternal exposures during the preconception period and to further elucidate causality through intervention studies. The ubiquity of these emerging nutritional and environmental exposures makes this area of inquiry of considerable public health importance.

Infant feeding and growth: putting the horse before the cart

Background

Previous observational studies have consistently shown slower weight and length gains in infants with prolonged breastfeeding than in those who were formula-fed from birth or breastfed for a shorter duration. These studies inferred that prolonged breastfeeding causes slower growth in infancy.

Objective

We compared infant growth associated with ≥12 mo of breastfeeding with a shorter duration of breastfeeding on the basis of 3 different analytic approaches to the same data from a randomized trial: intention-to-treat (ITT; "as randomized"), observational ("as fed"), and instrumental variable (IV; by using randomization as an "instrument" to achieve ≥12 mo of breastfeeding).

Design

This was a cluster-randomized trial of a breastfeeding-promotion intervention. Anthropometric measurements were obtained at birth and at 1, 2, 3, 6, 9, and 12 mo.

Results

The 3 analytic approaches yielded different results. The ITT approach showed more rapid growth in the first 2 mo among infants randomly assigned to the breastfeeding-promotion intervention than among control infants, with a decreasing difference over the ensuing months and nearly identical weight, length, and body mass index by 12 mo. The observational analysis showed a different trend: higher weight and length in infants who were breastfed ≥12 mo than in those who were breastfed <12 mo during the first 3 mo and no difference by 6 mo, while infants who were breastfed <12 mo showed increasingly higher weight and length from 6 to 12 mo. The IV analysis showed a temporal pattern that was similar to that seen in the ITT analysis, but with larger (and less precise) differences between infants breastfed for ≥12 compared with <12 mo.

Conclusions

We observed major differences in experimental (ITT and IV) compared with observational approaches to analyzing data obtained from the same children. These approaches lead to opposite causal inferences about the relation between infant feeding and growth and underline the importance of ensuring that the postulated cause (feeding) temporally precedes its hypothesized effect (growth). This trial is registered at http://www.isrctn.org/ as ISRCTN37687716.

Improving the use of research evidence in guideline development: 7. Deciding what evidence to include

BACKGROUND

The World Health Organization (WHO), like many other organisations around the world, has recognised the need to use more rigorous processes to ensure that health care recommendations are informed by the best available research evidence. This is the seventh of a series of 16 reviews that have been prepared as background for advice from the WHO Advisory Committee on Health Research to WHO on how to achieve this.

OBJECTIVES

We reviewed the literature on what constitutes "evidence" in guidelines and recommendations.

METHODS

We searched PubMed and three databases of methodological studies for existing systematic reviews and relevant methodological research. We did not conduct systematic reviews ourselves. Our conclusions are based on the available evidence, consideration of what WHO and other organisations are doing and logical arguments. KEY QUESTION AND ANSWERS: We found several systematic reviews that compared the findings of observational studies with randomised trials, a systematic review of methods for evaluating bias in non-randomised trials and several descriptive studies of methods used in systematic reviews of population interventions and harmful effects. What types of evidence should be used to address different types of questions? The most important type of evidence for informing global recommendations is evidence of the effects of the options (interventions or actions) that are considered in a recommendation. This evidence is essential, but not sufficient for making recommendations about what to do. Other types of required evidence are largely context specific. The study designs to be included in a review should be dictated by the interventions and outcomes being considered. A decision about how broad a range of study designs to consider should be made in relationship to the characteristics of the interventions being considered, what evidence is available, and the time and resources available. There is uncertainty regarding what study designs to include for some specific types of questions, particularly for questions regarding population interventions, harmful effects and interventions where there is only limited human evidence. Decisions about the range of study designs to include should be made explicitly. Great caution should be taken to avoid confusing a lack of evidence with evidence of no effect, and to acknowledge uncertainty. Expert opinion is not a type of study design and should not be used as evidence. The evidence (experience or observations) that is the basis of expert opinions should be identified and appraised in a systematic and transparent way.

Gaps in the evidence for well-child care: a challenge to our profession

BACKGROUND

Up to one third of visits to pediatricians involve health supervision (well-child care), and recommendations for office-based preventive interventions have dramatically expanded. We reviewed the evidence for the effectiveness of these interventions.

METHODS

The well-child care recommendations of 7 major North American organizations were tabulated. Three types of health supervision interventions were recommended, ie, behavioral counseling, screening, and prophylaxis. For recommendations common to at least 2 of the 7 organizations, evidence of effectiveness was sought from systematic reviews and clinical trials. Immunizations were not considered for this review, because they have been reviewed elsewhere.

RESULTS

Forty-two preventive interventions were recommended by > or =2 of the organizations. Limited clinical trials show that counseling can change some health risk behaviors; repeated intensive counseling is most likely to be effective. Harmful effects were shown for a few behavioral counseling interventions. Trials have been conducted for only 2 of the recommended screening interventions; therefore, rigorous evidence supporting screening is very limited. Trials support the use of folate to prevent neural tube defects, trials of iron supplementation do not address developmental outcomes, and trials were not found for the other recommended prophylactic interventions.

CONCLUSIONS

Limited direct evidence was found to support the recommended interventions. Because a large number of interventions are routinely recommended and often mandated and because the implementation of any recommendation may cause harm (including the displacement of other beneficial activities), these recommendations should be based on the strongest possible evidence. When recommendations are made, supporting evidence should be clearly stated.