Folic Acid & Colon Cancer

Not Too Much, Not Too Little, but Just Right…


A line from Goldilocks, or the new recommendations for daily folate/folic acid intake?  In the past, several studies have revealed a link between lower levels of folate intake and a higher incidence of colorectal adenomas, supporting the recommendation for individuals to take a daily multivitamin containing folate.  Recently, two new studies revealed conflicting results on the levels of folate necessary to protect against colorectal cancer.  


Good Dietary Sources
of Folate

Below are several common foods which can serve as excellent sources of folate.

Fortified Breakfast Cereals
¾ cup = 100-40 mcg

Blackeyed Peas
½ cup = 105 mcg

Spinach , frozen, cooked
½ cup = 100 mcg

4 spears = 85 mcg

Baked Beans
1 cup = 60 mcg

Green Peas, frozen, boiled
½ cup = 50 mcg  

Broccoli, cooked
½ cup = 50 mcg  

1 ounce = 40 mcg

Romaine Lettuce
½ cup = 40 mcg  

Orange Juice
¾ cup = 35 mcg      

Bread white/whole wheat
1 slice = 25 mcg 

Note that folate content is meausred in micrograms (mcg) and that 400 mcg  represents 100% of the US RDA for folate.

In the first study, researchers challenged the widely held belief that folate protects against colorectal cancer by showing that low circulating levels, rather than high levels, of the this B vitamin actually led to a reduced risk of colon cancer. 

Although, this study directly contradicts the findings of other epidemiological
studies that revealed an inverse relationship between folate intake and colorectal cancer risk, it does provide important information since it was performed in Sweden where the food is not fortified with folate. This study would not be able to be replicated in the United States because of the mandatory folic acid fortification program implemented in 1998. 

In a subsequent study, researchers examined the effects of folate on a laboratory model of colorectal cancer

development in mice.  They discovered that animals consuming a folate-deficient diet developed intestinal masses, while those mice on a control diet consuming adequate amounts of folate remained free of tumors.  The researchers concluded that folate deficiency increased DNA damage by decreasing the expression of two genes involved in DNA repair.  This study is consistent with the majority of epidemiological studies in humans, which demonstrate a clear link between colorectal cancer development and inadequate folate consumption. 

So where does that leave those of us who are concerned with consuming the right amount of folate?  Given the number of studies supporting high daily intake (≥400 ug/day) of folate and decreased colorectal cancer risk compared with the results of the Swedish study it is easy to become confused regarding recommendations for adequate folate consumption.  A practical recommendation would be to

follow the U.S. Recommended Daily Allowance (RDA) for folate, which is 400 ug/day for adults and children over 14.  This requirement can easily be achieved by eating a balanced diet, without the need for supplementation.  As
with most things even folate intake requires moderation. See the sidebar (right) for a variety of readily available dietary sources of folate.  Folate is obtained from  green leafy vegetables, legumes, nuts, and some dairy foods.  Fortified grain products such as bread, cereal and flour are also excellent sources of folate.