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Meta-Analysis
. 2018 Aug;21(12):2345-2350.
doi: 10.1017/S1368980018000575. Epub 2018 Mar 26.

Source of bias in sugar-sweetened beverage research: a systematic review

Ethan A Litman  1 , Steven L Gortmaker  2 , Cara B Ebbeling  3 , David S Ludwig  3
Affiliations
Meta-Analysis

Source of bias in sugar-sweetened beverage research: a systematic review

Ethan A Litman et al. Public Health Nutr. 2018 Aug.

Abstract

Objective: Financial conflicts of interest involving the food industry have been reported to bias nutrition studies. However, some have hypothesized that independently funded studies may be biased if the authors have strong a priori beliefs about the healthfulness of a food product ('white hat bias'). The extent to which each source of bias may affect the scientific literature has not been examined. We aimed to explore this question with research involving sugar-sweetened beverages (SSB) as a test case, focusing on a period during which scientific consensus about the adverse health effects of SSB emerged from uncertainty.

Design: PubMed search of worldwide literature was used to identify articles related to SSB and health risks published between 2001 and 2013. Financial relationships and article conclusions were classified by independent groups of co-investigators. Associations were explored by Fischer's exact tests and regression analyses, controlling for covariates.

Results: A total of 133 articles published in English met inclusion criteria. The proportion of industry-related scientific studies decreased significantly with time, from approximately 30 % at the beginning of the study period to <5 % towards the end (P=0·003). A 'strong' or 'qualified' scientific conclusion was reached in 82 % of independent v. 7 % of industry-related SSB studies (P<0·001). Industry-related studies were overwhelmingly more likely to reach 'weak/null' conclusions compared with independent studies regarding the adverse effects of SSB consumption on health (OR=57·30, 95 % CI 7·12, 461·56).

Conclusion: Industry-related research during a critical period appears biased to underestimate the adverse health effects of SSB, potentially delaying corrective public health action.

Keywords: Conflicts of interest; Diabetes; Nutrition; Obesity; Public health; Sugar-sweetened beverages.

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Conflict of interest statement

One investigator (E.A.L.) independently abstracted information regarding financial sponsorship for each selected manuscript. Another investigator (D.S.L.), masked to the article context (including conclusion strength ratings), used the abstracted information to categorize funding source as: (i) ‘industry-related’, including for-profit and non-profit affiliations with the SSB industry (e.g. American Beverage Association); (ii) ‘independent’, for government, university, independent foundations, philanthropies and other philanthropic organizations without direct association with the SSB industry; or (iii) ‘both.’

As an additional method to identify conflicts of interest prior to consistently enforced disclosure requirements( 21 ), we used the Integrity in Science Database( 22 ) to assign: (i) ‘conflict present’, if the first or last author ever received funding from an SSB industry-sponsored organization or had been affiliated with such an organization; or (ii) ‘conflict absent’.

Figures

Fig. 1
Fig. 1
Flowchart of articles included in the present review
Fig. 2
Fig. 2
Decreasing proportion of industry-related scientific studies on sugar-sweetened beverages (formula image) over the study period (formula image, linear regression line: P<0·001). (Too few articles were published in 2001 and 2002 to provide meaningful data for the regression)
See this image and copyright information in PMC

References

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