Scientific research funded by the soft drinks industry is up to eight times more likely than independent studies to suggest that its products are healthy, according to the first detailed analysis of the topic released on Monday.

A study by doctors in Plos Medicine, an open-access, peer-reviewed US medical journal published monthly online by the Public Library of Science (PLoS), a nonprofit organization, highlighted the potential for considerable bias in articles about soft drinks, fruit juices and milk in leading nutrition journals.

Medline searches of worldwide literature were used to identify three article types (interventional studies, observational studies, and scientific reviews) about soft drinks, juice, and milk published between 1 January, 1999 and 31 December, 2003. Financial sponsorship and article conclusions were classified by independent groups of coinvestigators. The relationship between sponsorship and conclusions was explored by exact tests and regression analyses, controlling for covariates. 206 articles were included in the study, of which 111 declared financial sponsorship. Of these, 22% had all industry funding, 47% had no industry funding, and 32% had mixed funding. Funding source was significantly related to conclusions when considering all article types (p = 0.037). For interventional studies, the proportion with unfavorable conclusions was 0% for all industry funding versus 37% for no industry funding (p = 0.009). The odds ratio of a favorable versus unfavorable conclusion was 7.61 (95% confidence interval 1.27 to 45.73), comparing articles with all industry funding to no industry funding.

Of the 206 articles, more than half of those who disclosed sponsorship were fully or partly funded by the industry. Those that were industry-sponsored were between four and eight times more likely to draw favourable conclusions.

David Ludwig, associate professor of paediatrics at the Children’s Hospital in Boston, stressed that there were many possible explanations for the results, but that the findings made the case for greater independent research on the health effects of nutrition. “The relatively small costs of more government funding could be drowned by the huge public health costs [of the status quo],” he said.

“I’m not surprised,” said Tim Lang, professor of food policy at City University in London in a comment to the Financial Times. “The sensitivity of nutrition for industry cannot be under-estimated. It has become a competitive advantage for companies and puts academics into a compromising position. The pendulum has swung too far.”

Examples included two on the positive effects of milk on bone mass and nutrients in the elderly supported by the US and Australian dairy industry; improved lipid levels of orange juice funded by Tropicana; and the absence of any link between dehydration and cola or coffee, funded by Coca-Cola.

Public and foundation-funded studies suggested few preventive effects of milk on hip fractures, diabetes and cancers; a risk of kidney stones from Cola; and obesity linked to consumption of soft drinks.

Plos Medicine says that support of biomedical research may bias scientific conclusions, as demonstrated by recent analyses of pharmaceutical studies. It concludes that industry funding of nutrition-related scientific articles may bias conclusions in favor of sponsors' products, with potentially significant implications for public health.