Folate status shows no relationship with vitamin B12 but reiterates the urgency for folate fortification in the UK

The UK has a high and increasing prevalence of folate deficiency. The decision to start mandatory folic acid fortification has not yet been implemented. Concern has been raised about the effect of high folate on vitamin B12 status.

The prevalence of folate deficiency was assessed based on the serum folate concentrations from 47,240 samples collected between August 2023 and January 2025 (provided to us as anonymised data, measured in a UK-based contract laboratory using an immunochemical analyser). In 39,374 individuals, both serum folate and holotranscobalamin (holoTC) ('active' vitamin B12) concentrations were available, and were used to determine if high folate status had a negative impact on active vitamin B12 concentrations.

For women of reproductive age (16-50 y), 72.7% had serum folate concentration lower than 24.3 nM/L for protection against neural tube defects. For young adult women (21-25 y) this percentage was 85.5%. The top decile, across all samples (mean serum folate = 43.9 nM/L, range 38.4- > 45 nM/L, n = 3935), had on average also a high holoTC concentration (119.2 pM/L) and no increased risk of vitamin B12 deficiency.

Young women are especially a risk of low folate status. We found no evidence that high folate affects vitamin B12 status.