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In prior studies of B6 and B12 supplementation, researchers reported excess hip fracture risk among supplement users. To confirm these results in a large population, investigators used data from the Nurses' Health Study. They assessed more than 75,000 postmenopausal women at baseline and every 2 years from 1984 through 2014 (mean follow-up, 21 years) for a wide range of clinical variables; dietary analyses were performed every 4 years.
Median intakes (dietary plus supplements) of vitamins B6 and B12 were 3.6 mg/day and 12.1 µg/day, respectively. About 9% of the population had high intake of B6 (≥35 mg/day) and about 24% had high intake of B12 (≥20 µg/day). Nonpathological hip fractures occurred in 2300 participants. High intake of both B6 and B12 was associated with nearly double the crude incidence of hip fracture compared with low intake of both vitamins (19 vs. 10 per 10,000 person-years) but statistical adjustment attenuated the relative risk to about 1.5.
Meyer HE et al. Association of high intakes of vitamins B6 and B12 from food and supplements with risk of hip fracture among postmenopausal women in the Nurses' Health Study. JAMA Netw Open 2019 May 3; 2:e193591. (https://doi.org/10.1001/jamanetworkopen.2019.3591)
Comment
We don't have a known mechanism by which B6 or B12 would cause fractures, so inferring a causal association would be purely speculative. However, nutritional supplements do not seem to benefit people without diagnosed nutritional deficiencies, and excessive intake of some vitamins and minerals can be harmful. Therefore, this study reminds us to question patients explicitly about nutritional supplement use and counsel them accordingly.