Article in the Telegraph:
"Folic acid is the synthetic form of a naturally occurring B vitamin, folate. Women who have good levels of folate in their diet, or take folic acid supplements, are far less likely to have babies affected by the birth defect spina bifida. America and Canada started adding folic acid to flour in 1998 and the Food Standards Agency (FSA) in the UK has called for a similar fortification here. But recent research has linked high folic acid consumption with an increased risk of bowel cancer; the modest-sounding annual increase of one per cent could, in fact, amount to an extra 3,000 cases per year in the UK. Other evidence points to an increased risk of breast or prostate cancers."
""People with a high intake end up with unmetabolised folic acid floating in their bloodstream," says Dr Siân Astley of the Institute for Food Research in Norwich. "We don't really know what its consequences might be."
The recommended daily intake for folate is 200 micrograms (mcg), and most multivitamins contain this amount of folic acid. But it is also added to breakfast cereals, snack bars and some margarines. Official government advice puts the safe upper limit for folic acid at 1,000mcg per day, but the leading vitamin B expert, Prof David Smith of Oxford University, thinks there is now sufficient evidence to cut that down to 500mcg in general and 400mcg for cancer survivors.
"If you eat a lot of fortified cereals, you may want to rethink your daily multivitamin. Or you could stick with the vitamin pill and switch to wholegrains without added synthetic vitamins, such as porridge or muesli," says Dr Astley. "Fortification is an overly broad approach that increases everyone's folic acid intake, instead of targeting those who need it."
Cutting down on salt/sodium intake lowers the risk of most cancers.