Vitamin C intake in relation to bone mineral density and risk of hip fracture and osteoporosis: a systematic review and meta-analysis of observational studies

We aimed to systematically review available data on the association between vitamin C intake and bone mineral density (BMD), as well as risk of fractures and osteoporosis, and to summarise this information through a meta-analysis. Previous studies on vitamin C intake in relation to BMD and risk of fracture and osteoporosis were selected through searching PubMed, Scopus, ISI Web of Science and Google Scholar databases before February 2017, using MeSH and text words. To pool data, either a fixed-effects model or a random-effects model was used, and for assessing heterogeneity, Cochran's Q and I-2 tests were used. Subgroup analysis was applied to define possible sources of heterogeneity. Greater dietary vitamin C intake was positively associated with BMD at femoral neck (pooled r 0.18; 0.06, 0.30) and lumbar spine (pooled r 0.14; 95 % CI 0.06, 0.22); however, significant between-study heterogeneity was found at femoral neck: I-2 = 87.6 %, P-heterogeneity<0.001. In addition, we found a non-significant association between dietary vitamin C intake and the risk of hip fracture (overall relative risk = 0.74; 95 % CI 0.51, 1.08). Significant between-study heterogeneity was found (I-2 = 79.1 %, P-heterogeneity<0.001), and subgroup analysis indicated that study design, sex and age were the main sources of heterogeneity. Greater dietary vitamin C intake was associated with a 33 % lower risk of osteoporosis (overall relative risk = 0.67; 95 % CI 0.47, 0.94). Greater dietary vitamin C intake was associated with a lower risk of hip fracture and osteoporosis, as well as higher BMD, at femoral neck and lumbar spine.