To the Editor: The recent viewpoint by Kamien1 and letter by Gunasekera2 rightly highlight the benefits of folate fortification and the unlikely occurrence of masking pernicious anaemia. Food Standards Australia New Zealand recently submitted a proposal supporting the mandatory fortification of bread-making flour to increase folate intakes in women of child-bearing age, with the aim of reducing the risk of children being born with neural tube defects.3 This proposal has had extensive public comment and will be considered by the Australia and New Zealand Food Regulation Ministerial Council. Several public groups and individuals continue to raise concerns that higher dietary folate levels could increase B12 deficiency. Our data, collected from a population-based sample of 2596 older people in the Blue Mountains region, from 1997 to 2000, do not suggest that this is a likely outcome.

We recently reported the prevalence of low serum vitamin B12 levels in the Blue Mountains Eye Study cohort of people aged 50 years and older. We found that 22.9% had low serum B12 levels (< 185 pmol/L).4 New data from this study show that higher intakes of folate (from diet and supplements) did not increase the likelihood of low serum B12 levels; in fact, people whose diets included folate in the highest quintile of intake had significantly higher serum B12 levels than those consuming lower dietary folate (Box), after accounting for age and sex (P < 0.001). After also adjusting for vitamin B12 from diet and supplements, there was no significant difference in mean serum B12 levels for the various quintiles of folate intake.

We also investigated older people who reported consuming high amounts of folate (> 500 μg dietary folate equivalents [DFE] [n = 645] and > 1000 μg DFE [n = 123]) and found higher mean serum B12 levels in these groups than in people who consumed < 500 μg DFE, after adjusting for age and sex (P for trend < 0.001). After further adjustment for vitamin B12 intake, there were no significant differences in mean serum B12 levels for these high dietary folate intakes (Box).

We also examined the frequency of macrocytic anaemia in our cohort (n = 6; 0.2%); two of these had low serum B12 levels (0.3% of subjects with low serum B12 levels).

In the United States, where mandatory folate fortification began a decade ago, a study of the presence of anaemia in people with B12 deficiency found no significant change in the proportion with anaemia before and after the introduction of mandatory fortification.5

Although many older Australians have low serum levels of vitamin B12, our data show that higher intakes of folate do not increase the likelihood of low serum B12 levels. Given the relatively high prevalence of low serum B12 levels among older people, it would seem reasonable for this to be monitored more frequently in this age group. We suggest that this is not a valid concern that should prevent moves to proceed with mandatory folate fortification of key foods in Australia.