The UK's Food Standards Agency (FSA) recently rec-ommended mandatory folic-acid fortification of either bread or flour as part of an effort to prevent neural-tube defects (NTDs) such as spina bifida and anencephaly.
In the US, they have been fortifying flour with folic acid since 1996, and NTDs dropped by 20 per cent (BMJ, 2007; 334: 1252). The UK's Scientific Advisory Committee on Nutrition (SACN) report on Folate and Disease Prevention (2006) says that it could prevent up to 162 NTDs a year.
Yet, although fortification seems like a good idea, the evidence suggests that, for some, it could do more harm than good. More disturbing is that folic-acid supplementation could lead to cancer.
In the latest study to raise a cautionary note regarding the wisdom of mass medication with folic acid, researchers followed more than 1000 men and women, who had previously had precancerous adenomas removed from their colon, for six to eight years. Half received 1 mg/day of folic acid and half received a placebo. On follow-up, there was a 67-per-cent higher risk of advanced lesions in the folic-acid group, and a more than twofold increased risk of having at least three adenomas. Moreover, those taking folic acid were also more likely to develop cancers other than bowel cancer-particularly prostate cancer (JAMA, 2007; 297: 2351-9).
Although the dose used in the study is higher than recommended by the FSA in bread, the fact that other foods are also fortified with folic acid makes this worrying. A significant number of people may end up getting too much, enough to cause serious damage.
Scientists report that colon-cancer cases in both the US and Canada spiked after folic fortification of cereals in the late 1990s. Increased consumption of folic acid, the researchers said, was a likely explanation (Cancer Epidemiol Bio-markers Prev, 2007; 16: 1325-9).
So, how does a nutrient thought to be cancer-protective become a cancer-promoter? According to scientists at the Fred Hutchinson Cancer Research Center in Seattle, WA, it's all to do with timing. While folate may prevent tumours from forming in the first place, once cancer starts, the vitamin can feed its growth (JAMA, 2007; 297: 2408-9). So, fortification may benefit younger con-sumers, but be detrimental in older ones. This 'dual-effect' has also been seen in animal and laboratory studies (Environ Mol Mutagen, 2004; 44: 10-25).
It's also possible that synthetic folic acid is the problem. In a study of 25,000 postmenopausal women, there was no breast-cancer risk with folate from food, but the risk increased significantly (32 per cent) with high folate supplementa-tion (Am J Clin Nutr, 2006; 83: 895-904).
Other adverse effects
And cancer isn't the only problem. According to the SACN 2006 report, excess folic acid may mask vitamin B12 deficiency in the elderly, and possibly lead to "irreversible neurolog-ical damage". While the evidence is limited to "often poorly described case reports", some researchers note that it's nonetheless a "major concern" (Am J Clin Nutr, 2004; 80: 1123-8).
There's also evidence that, rather than 'protecting' pregnant women, folic acid can increase early mis-carriage. Although associated with fewer NTDs and other anomalies, it increases spontaneous abortion. In fact, for every 1000 women on folic-acid supplementation who became preg-nant, there would be 10 fewer birth defects, but 18 more miscarriages (Lancet, 1997; 350: 513-5).
The evidence, however, is far from conclusive: a more recent study found no evidence that 400 mg/day of folic acid before and during early pregnancy influenced the risk of miscarriage (Lancet, 2001; 358: 796-800).
Some suggest that folic acid is a weak abortifacient, and prevents birth defects by helping the body reject the malformed baby-while encouraging rejection of other babies, too. Others suggest that high concentrations of folic acid leads to higher rates of fetal complications and distress (Am J Clin Nutr, 1984; 40: 496-507).
It also appears that too much folic acid can increase allergies. Women who supplemented throughout pregnancy (rather than preconceptually and for the first two months of pregnancy) had babies with more allergic skin reactions, asthma and bronchitis (Arch Dis Child, 1994; 70: 229-33).
Clearly, more research is needed to establish the effects of mass fortifica-tion on the whole of the population.
As Dr Arthur Schatzkin, chief of the nutritional epidemiology branch at the National Cancer Institute, points out, "When you focus on a magic bullet, sometimes you find collateral damage."
To supplement or not?
- Monitor your total level of dietary folate closely to make sure you don't get too much or too little. Avoid fortified foods, which will be processed anyway.
- Much of your daily requirement (adults require at least 0.2 mg/day) can probably come from a varied and balanced diet. Stick to natural sources such as fruits (including oranges, strawberries and melons), dark-green leafy vegetables, liver, and dried beans and peas.
- If you need to supplement, take folic acid as part of a general B complex
or multivitamin. Don't take it on its own.
- If you are planning a baby, studies show that the best effect is when folic acid is taken as part of a complex starting before conception and continued into early pregnancy. The UK Food Standards Agency recommends a
daily supplement of 0.4 mg starting after stopping contraception until week 12 of pregnancy. Thereafter, supplement holistically.