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Does Fish Oil Lower Asthma Risk? The New England Journal of Medicine reported on a study of fish oil consumption in pregnant mothers and the subsequent development of asthma in their children. Read the excerpts from the abstract and answer the questions that follow: (Source: Bisgaard et al., "Fish oil- derived fatty acids in pregnancy and wheeze and asthma in offspring," New England Journal of Medicine, vol. 375 [December 2016]: 2530-2539, doi: 10.1056/NEJMoa1503734 Methods: We randomly assigned 736 pregnant women at 24 weeks of gestation to receive fish oil or a placebo (olive oil) daily. Neither the investigators nor the participants were aware of group assignments during follow-up for the first 3 years of the children's lives, after which there was a 2 -year follow- up period during which only the investigators were unaware of group assignments. Results: A total of 695 children were included in the trial, and \(95.5 \%\) completed the 3-year, double-blind follow-up period. The risk of persistent wheeze or asthma in the treatment group was \(16.9 \%\), versus \(23.7 \%\) in the control group, corresponding to a relative reduction of \(30.7 \%\). a. Was this a controlled experiment or an observational study? Explain how you know. b. Assuming the study was properly conducted, can we conclude that the lower rate of asthma was caused by the mother's consumption of fish oil?

Step by step solution

01

Controlled Experiment or Observational Study

Firstly, to identify whether this study is a controlled experiment or an observational study, understand that in a controlled experiment, an intervention is deliberately applied to some individuals and is then compared with other individuals who were not subjected to this treatment. Observational study, on the other hand, observes individuals and measures variables of interest without affecting responses. In this case, the study is a controlled experiment. This is because pregnant women at 24 weeks of gestation were randomly assigned to receive fish oil or a placebo (olive oil) daily.

02

Determining Causality

Secondly, in order to conclude whether the lower rate of asthma was caused by the mother's consumption of fish oil, you can refer to the results of the controlled experiment. If the study is indeed properly conducted, a causal relationship is plausible due to the experimental setting and random allocation of treatment. The results show that the risk of persistent wheeze or asthma was lower in the treatment group compared to the control group, which verifies the difference in the groups. Therefore, it can be concluded that mother's consumption of fish oil resulted in a lower rate of asthma.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Observational Study

An observational study involves observing subjects and measuring variables of interest without influencing those variables. In such studies, researchers gather data on subjects in their natural environments without attempting to manipulate the study conditions or apply any treatment. For example, if researchers were to simply observe pregnant women as they naturally consume different amounts of fish oil and follow up on their children's asthma rates later on, this would be classified as an observational study. There is no intervention; researchers only record findings from naturally occurring behaviors.

• No manipulation of study conditions
• Data collection happens in natural settings
• Results can highlight associations but not causations

It's important to note that observational studies can suggest associations but they do not establish a cause-and-effect relationship between the variables involved.

Causality in Experiments

In scientific research, establishing causality is important when determining whether one variable directly affects another. Causality refers to a situation where a change in one variable directly produces a change in another. In controlled experiments, causality is more reliably established because the experimental design allows researchers to manipulate one or more independent variables and observe the effect on dependent variables. In the case of the fish oil study, causality is suggested because:

• The researchers controlled the intake of fish oil and olive oil (placebo) among the study participants.
• The effects on children's asthma and wheeze were measured.
• The reduction in asthma risk in children whose mothers consumed fish oil indicates that fish oil could cause this effect.

This approach strengthens the confidence that the observed differences were caused by the intervention and not other extraneous factors.

Randomized Control Trials

Randomized control trials (RCTs) are a robust method for testing the efficacy or effects of an intervention. RCTs randomly assign participants to either the treatment group or the control group. This random assignment helps to ensure that any other variables are evenly distributed across both groups and that the comparison between groups is fair and unbiased. Key features of RCTs include:

• Random assignment of participants
• Control group receives placebo or standard treatment
• Blinded or double-blinded setup to minimize bias

In the study, 736 pregnant women were randomly assigned to receive fish oil or a placebo. This randomization and the double-blind setup in place for the initial three years help to ensure that the results reflect the actual effects of fish oil, rather than other factors.

Asthma Risk Reduction

Asthma risk reduction aims to lower the likelihood of developing asthma or related respiratory conditions. Reducing risk factors during crucial periods, such as pregnancy, can significantly impact future health outcomes of offspring. In this study:

• Fish oil supplementation during pregnancy was tested for its potential to reduce the asthma risk in children.
• The results showed a lower incidence of asthma and persistent wheeze in the children of women who consumed fish oil.
• A relative reduction of 30.7% was observed in the treatment group compared to the control group.

These findings contribute to the understanding of dietary factors during pregnancy that may protect children from developing asthma, offering a potential preventive measure.