I must admit, I thought they'd been supplementing for a while. I know they were discussing it many years ago. I didn't realise that it hadn't been implemented.
The link you provide says that large doses of folic acid shouldn't be given for megaloblastic anaemia in case of B12 deficiency. That means doses in the 1000's of ug. I'm pretty sure that folate in bread would result in much smaller doses.
I believe that very ordinary doses, such as 400 micrograms of folic acid, can be sufficient to mask B12 deficiency. The amount we'd be likely to get from wheat flour alone likely wouldn't fully mask.
But there's always the person who eats nothing but toast, pizza...
"Several studies both before and after fortification have examined this issue and concluded that, at current recommended intakes, there is little evidence of masking or exacerbation of neuropathies [61,62,63,64]."
I live in the US where fortification has been done since 1998. I believe masking of enlarged blood cells by folic acid was one reason my B12 deficienciency/PA wasn't detected early and I ended up with nerve damage. For several years I had mentioned fatigue to my doctors but nothing was ever found in the standard tests doctors usually run, TSH and CBC. After foot surgery I experienced severe neurological symptoms, but my MCV was not higher than the normal range so nothing unusual was detected in the CBC blood test. Most traditional doctors here aren't aware of B12 deficiency and the symptoms or order a B12 test. It was 3-1/2 months after my surgery before an ER doctor even thought to order a B12 test.
I ate lots of leafy greens, veggies, etc. so likely got plenty of folic acid in my diet, plus whatever was in bread and pasta that I consumed often. My folate level was quite high when my B12 deficiency was finally diagnosed (perhaps because my B12 was low so the folate accumulated?)
Dr. Ralph Green in the following article is one of the experts who appears in the well known YouTube video about B12 deficiency, youtube.com/watch?v=BvEizyp...
There are many other articles about the masking effect, links to some of them are below. Sally Pacholok warns about the masking by folic acid fortification in her book "Could It Be B12? An Epidemic of Misdiagnosis."
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