Yes, it seems to. In rats with breast cancer. At doses two-to-five times higher than humans consume. The fairly comprehensive study analysis (here) covers much of the literature on folic acid, showing that the addition of folic acid doesn’t seem to help and may add to the problem in colon cancer as well.
The problem with human studies on folic acid is that it is a required addition to our diets. Where in our diets does it occur? “Since 1998, it has been added to cold cereals, flour, breads, pasta, bakery items, cookies, and crackers, as required by federal law. ” (from WebMD) According to that fountain of wisdom, wikipedia, seventy-six other countries have followed the U.S. lead and require folic acid in their floured goods. What else does a diet high in white flour treats cause? Obesity. Is obesity associated with increased breast cancer? Yes.
So how do you tease out folic acid from the products you find folic acid in? Let’s remember that folic acid is necessary for human life, and the people who are supposed to take the most of it are pregnant mothers. Even without a deficiency, it is supposed to be good for avoiding neural tube defects in babies. So how do we get from an essential for babies to possibly cancer causing?
Could it be that synthetic folate is an issue? According to Pubchem, folic acid has an extraordinary absorption and reabsorption rate. The gut absorbs it all, and the liver stores it. Even when the liver dumps it out in the bile, it is reabsorbed through the gut again. Any folic acid in the blood stream is continuously reabsorbed by the kidney. This is a compound that the human body conserves every chance it gets.
According to Erica Wickham, R.D., it is virtually impossible to poison yourself with dietary folate. Pub chem concurs, noting that dietary folate is absorbed only half as fast. So synthetic folic acid is likely the culprit. Wickham notes that too much folate masks B12 deficiency and can lead to a zinc deficit.
Zinc deficiency, particularly caused by a mutation in zinc binding ability in breast cancer patients, leads to: “significantly decreased disease-free and overall survival.” (study on mutation here).
Vitamin B12 below a certain threshold is also associated with increased risk of breast cancer. (here)
So what really do we learn from the rat study on folic acid? Possibly that very high levels of folic acid,without supplementing other necessary compounds, can lead to a deficiency and even mask a deficiency of necessary nutrients. If I recall, this is simply a reiteration of previous studies showing that taking too many supplements may not be a good idea if your body is already dealing with cancer. (recent review here).
Before we look too closely at supplements as a culprit, I think it might be time to look at why we need to fortify our white flour worldwide. We’ve got dozens of studies looking at our dietary choices, and the lives saved from making some minor changes there would dwarf those saved if we pulled every folic acid supplement in the world off the shelves tomorrow.