From the Research
Excessive vitamin B12 intake can be harmful, particularly when combined with high intakes of vitamin B6, as it may increase the risk of hip fracture in postmenopausal women. The body absorbs only what it needs and eliminates the excess through urine, making toxicity rare even with high doses. Vitamin B12 is water-soluble, so it doesn't accumulate in tissues like fat-soluble vitamins can. Most healthy individuals can safely take doses well above the recommended daily allowance (2.4 micrograms for adults) without experiencing adverse effects. However, very high doses might occasionally cause mild side effects like headache, nausea, dizziness, or skin rash in sensitive individuals.
Some key points to consider:
- A study published in 2019 1 found that high intakes of vitamins B6 and B12 from food and supplements were associated with an increased risk of hip fracture in postmenopausal women.
- The same study found that combined high intakes of both vitamins conferred a particularly increased fracture risk, with an almost 50% increased risk of hip fracture.
- Other studies have shown that vitamin B12 deficiency is a concern, particularly for vegetarians, vegans, older adults, and those with absorption issues, and that intranasal administration of vitamin B12 may be a safe and effective alternative to intramuscular injections 2.
- However, it is also important to note that high doses of vitamin supplements can be toxic, and there is no evidence that taking vitamin supplements without medical indication improves the health of people with a varied diet 3.
In terms of morbidity, mortality, and quality of life, it is essential to weigh the potential benefits of vitamin B12 supplementation against the potential risks, particularly in vulnerable populations such as postmenopausal women. Healthcare providers should consult with patients before recommending high-dose supplements, especially for those with certain medical conditions or taking other medications.