Disclosure of funding sources and conflicts of interest in evidence underpinning vitamin D and calcium recommendations in bone health guidelines

Objective: The present study aims to examine the relationship between study funding sources, author conflicts of interest (COI) and conclusions in studies supporting vitamin D and Ca intake cited in bone health guideline recommendations.

Design: Cross-sectional.

Setting: Forty-seven global bone health guidelines with vitamin D and/or Ca recommendations for adults aged 40 years and above.

Participants: The evidence cited to support the recommendations was extracted by two independent reviewers and classified by type of recommendation, article characteristics, study design, types of funding sources and conflict of interest (COI) disclosure and direction of study conclusions.

Results: Of 156 articles cited to support the bone health recommendations, 120 (77 %) disclosed a funding source, and 43 (28 %) declared that at least one author had a COI. Compared with articles with non-commercial or no funding source, those funded by commercial sponsors tended to have a study conclusion favourable towards vitamin D/Ca (relative risk (95 % CI): 1·32 (0·94, 1·87), P = 0·16), but the association was not statistically significant (Fisher's exact test). Compared to those with a COI disclosure statement, articles with missing or unclear COI disclosure were more likely to have favourable conclusions (1·56 (1·05, 2·31), P = 0·017) (Fisher's exact test).

Conclusion: In the evidence underpinning a sample of global bone health guidelines, COI disclosure was low and studies with missing or unclear COI disclosures were more likely to have favourable study conclusions than those with disclosures, suggesting a need for greater transparency of COI in bone health guidelines.