Methodological quality of recommendations on vitamin D and calcium recommendations - a systematic review of bone health guidelines

There are numerous guidelines developed for bone health. Yet it is unclear the differences in guideline development methods explain the variability in recommendations for vitamin D and calcium intakes. The objective of this systematic review was to collate and compare recommendations for vitamin D and calcium across bone health guidelines, assess methods used to form the recommendations, and explore which methodological factors were associated with these guideline recommendations. We searched MEDLINE, EMBASE, CINAHL and other databases indexing guidelines to identify records in English between 2009 and 2019. Guidelines or policy statements on bone health or osteoporosis prevention for generally healthy adults aged ≥40 years were eligible for inclusion. Two reviewers independently extracted recommendations on daily vitamin D and calcium intake, supplement use, serum 25 hydroxy vitamin D [25(OH)D] level, and sunlight exposure; assessed guideline development methods against 25 recommended criteria in the World Health Organization (WHO) Handbook for Guideline Development; and, identified types of evidence underpinning the recommendations. We included 47 eligible guidelines from 733 records: 74% of the guidelines provided vitamin D (200∼600-4000 IU/day) and 70% provided calcium (600-1200 mg/day) recommendations; 96% and 88% recommended vitamin D and calcium supplements, respectively; and 70% recommended a specific 25(OH)D concentration. The mean of meeting 25 WHO methodological criteria per guideline was 10 (95% CI: 9-12; interquartile range: 6-15). There was uncertainty in the associations between the methodological criteria and the proportion of guidelines that provided recommendations on daily vitamin D or calcium. Various types of evidence, ranging from previous bone guidelines, nutrient reference reports, systematic reviews, observational studies, to perspectives/editorials were used to underpin the recommendations. In conclusion, there is considerable variability in vitamin D and calcium recommendation and in guideline development methods in bone health guidelines. Effort is required to strengthen methodological rigor of guideline development and utilize the best available evidence to underpin public health nutrition.