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by CancerConnect, Medically Reviewed by Dr. C.H, Weaver M.D. 3/2022

Eating a well-balanced, plant-based diet may reduce your risk of developing certain forms of cancer. Research has shown that eating fruits and vegetables rich in folate is associated with a reduced risk of certain types of cancer. Specifically, folate and folic acid have been linked with potential reductions in the risk of breast, colon, rectal, and pancreatic cancers.

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What Is Folate?

Folate is a water-soluble B-vitamin that occurs naturally in foods such as spinach. Its synthetic form-folic acid-is found in dietary supplements and fortified foods - this form makes up a large part of the dietary intake in the United States.

The body absorbs and utilizes folic acid twice as efficiently as it does food sources of folate. Because they play an integral part in making DNA and RNA, folate and folic acid are responsible for producing and maintaining red blood cells. Proper red blood cell production serves important functions, including the prevention of anemia. Folate is also responsible for producing levels of homocysteine (an amino acid in the blood).

Food Sources of Folate

The best food sources of folate are green leafy vegetables such as spinach. Oranges and strawberries are also excellent sources of folate, as are some other fruits. Other foods that are rich in folate are legumes, such as dried peas and beans.

Folic acid was added to the U.S. food supply in the mid-1990s as a way to reduce the amount of neural tube defects in U.S. infants. These folic acid–enriched foods include dried cereal, white rice, and pasta; and the folic acid in these fortified foods is easier to absorb than the folate naturally present in other foods.

Daily Requirements of Folate

To prevent deficiencies in folate, a recommended daily allowance (RDA) has been established. Children between the ages of one and three need 150 micrograms (mcg) of folate per day. From ages four to eight, the RDA is 200 mcg. Teens ages nine to 13 need 300 mcg a day, whereas those 14 and older need 400 mcg. For women who are pregnant, the RDA is 600 mcg; if nursing, 500 mcg.

Taking large doses of folate or folic acid is not recommended because it may cause a lack of vitamin B12. The upper limit for folate in adults is 1,000 mcg per day unless instructed differently by a physician. A lack of vitamin B12 can present as another form of anemia and if not treated may result in permanent nerve damage.

Conditions Associated with Folate Deficiency

If one’s diet is lacking in folate or folic acid, the following may occur:

  • Increased risk of neural tube defects in infants
  • Anemia induced by folate deficiency (which can occur as weakness), sore tongue, headaches, irritability, memory problems, and behavioral issues. 
  • A lack of folate in the blood stream can also cause an increase in homocysteine, which increases the risk of developing heart disease.

People who are pregnant, abuse alcohol, have malabsorption problems, or suffer from kidney or liver disease have an increased need for folate through diet or supplementation. Taking certain medications may also impair folate absorption, which can increase need. These medications include: Dilantin® (phenytoin), Mysoline® (primidone), Fortamet® (metformin), Azulfidine® (sulfasalazine), Dyrenium® (triamterene), Rheumatrex® (methotrexate), and some barbiturates.

Reducing Cancer Risk with Increased Folate Intake?

Research has shown that a diet lacking in folate may increase the risk of developing colon, and pancreatic cancers.1,2 The most confirmatory evidence of this was seen in the Nurse’s Health Study, where researchers followed the dietary habits of 88,000 women over a 14-year period. 

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Researchers found that older women (ages 55 to 69) who consumed adequate amounts of folate through diet and a multivitamin had a lower risk of developing colon cancer. 

Another study found that Chinese women who consumed diets highest in folate or folic acid had a lower risk of breast cancer compared with their counterparts who consumed low amounts of folate. It’s also noted that alcohol negates the positive effect of folate in the diet. Researchers state that although these studies show promising results, more research needs to be done to establish a causal relationship.

According to combined analyses of several previously published studies however folate does not appear to influence the risk of developing breast cancer. These results were published in the Journal of the National Cancer Institute.3

Folate, Vitamin B6, Vitamin B12 Not Shown to Protect Against Cancer in Women

Supplementation with folic acid, B6, and B12 for more than seven years neither reduced nor increased the risk of breast cancer or other invasive cancer among women. These results were recently published in the Journal of the American Medical Association.4

The role of diet in cancer incidence remains a major focus among researchers as it is becoming more evident that diet may drastically reduce the risk of developing certain types of cancers. It has been suggested that diets high in folate and B vitamins reduce the risk of developing cancer; however, it has also been discovered that supplementation with specific vitamins and minerals often does not have the same protective role as obtaining the nutrients from foods.

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To further explore the relationship between folate and B vitamins, researchers affiliated with the Women's Antioxidant and Folic Acid Cardiovascular Study (WAFACS) evaluated the effects of supplementation on cancer. This trial included 8,171 postmenopausal healthcare professionals who were considered to be at a high risk of developing cardiovascular disease. To prevent cardiovascular disease, participants were randomized to daily combined folic acid (2.5 mg), vitamin B6 (50 mg), and vitamin B12 (1 mg) or placebo from 1998 to 2005. ?After just over seven years of being on the study, the following results were found:

  • There were no differences in the incidence of any single type of cancer between patients taking supplementation compared with those receiving placebo.
  • There were no differences in death from cancer between the two groups.

The researchers concluded that supplementation with folate and B vitamins does not appear to reduce the risk of developing or dying from cancer. Because this study included supplements, results do not necessarily reflect upon a diet high in food providing these nutrients.

References

  1. Larsson S, Hakansson N, Giovannucci E, Wolk A. Folate Intake and Pancreatic Cancer Incidence: A Prospective Study of Swedish Women and Men. Journal of the National Cancer Institute.*2006; 98: 407-413.
  2. La Vecchia C, Negri E, Pelucchi C, et al. Dietary folate and colorectal cancer. International Journal of Cancer. 2002;102:545-7.
  3. Meta-analyses of Observational and Genetic Association Studies of Folate Intakes or Levels and Breast Cancer Risk. Journal of the National Cancer Institute. 2006;98:1607-22.
  4. Zhang S, Cook N, Albert C, et al. Effect of Combined Folic Acid, Vitamin B6, and Vitamin B12 on Cancer Risk in Women: A Randomized Trial. Journal of the American Medical Association. 2008; 300:2012-2021.