Is Excessive Folic Acid Intake Linked to Cancer Risk?

Folic acid overdose

Hello, nutritionist.
Today I read in the newspaper that long-term excessive intake of folic acid (800 mcg) can lead to cancer.
I take one multivitamin in the morning (which contains 800 mcg of folic acid) and two B-complex vitamins (which contain 300 mcg of folic acid), totaling 700 mcg of folic acid, not to mention the folic acid from the fruits and vegetables in my three meals.
Doesn't that exceed 800 mcg of folic acid? I'm quite worried about this.

Zhihong, 30~39 year old female. Ask Date: 2009/11/20

Dr. Shi Guimei reply Nutrition

Dear Zhihong,
Hello! Previous studies have indicated that administering 10 mg (1000 micrograms equals 1 milligram) of folic acid daily at 25 times the recommended amount to women for four months did not result in any adverse symptoms.
However, consuming excessive amounts of folic acid, such as over 100 times the recommended daily intake, may lead to seizures.
Animal studies have shown that administering large doses of folic acid via injection may lead to accumulation in the kidneys, causing kidney damage.
In our country, the recommended dietary allowance for folic acid in adults is 400 micrograms per day.

It is important to maintain a balanced diet, and adults may supplement with a multivitamin if needed; however, it is not necessary to take both a multivitamin and a B-complex vitamin simultaneously.
Wishing you happiness and health!
Sincerely,
Dietitian Shih Kuei-Mei
Director of the Nutrition Department, Taoyuan Hospital, Ministry of Health and Welfare

Reply Date: 2009/11/20

More Info

Excessive intake of folic acid, particularly in the form of supplements, has been a topic of discussion in the medical community regarding its potential link to cancer risk. Folic acid is the synthetic form of folate, a B vitamin that is crucial for DNA synthesis, repair, and methylation. It plays a significant role in cell division and growth, which is why it is particularly important during periods of rapid growth, such as during pregnancy.

The concern about excessive folic acid intake stems from its potential effects on pre-existing cancer cells. Some studies suggest that high levels of folic acid may promote the growth of certain types of cancer, particularly in individuals who already have undiagnosed cancerous lesions. This is because folic acid can stimulate cell division, which could theoretically support the proliferation of cancer cells. However, the evidence is not definitive, and the relationship between folic acid and cancer risk remains complex and somewhat controversial.

The recommended dietary allowance (RDA) for folate for adults is about 400 micrograms (mcg) per day, with higher recommendations for pregnant women (600 mcg) and lactating women (500 mcg). The upper limit for synthetic folic acid intake from supplements is set at 1,000 mcg (1 mg) per day for adults. Your concern about exceeding this limit is valid, especially since you mentioned taking a multivitamin with 800 mcg of folic acid and additional B vitamins that contribute another 300 mcg. This totals 1,100 mcg from supplements alone, not accounting for the folate content in your diet from fruits and vegetables, which can further increase your intake.

While the body can tolerate some excess folic acid, consistently exceeding the upper limit may pose risks, particularly if there are underlying health issues or a history of cancer in your family. It is essential to consider the source of your folate intake. Natural food sources of folate, such as leafy greens, legumes, and fortified grains, are generally considered safe and beneficial for health. However, the synthetic form, particularly in high doses, should be approached with caution.

If you are concerned about your folic acid intake, it would be wise to consult with a healthcare professional, such as a registered dietitian or your primary care physician. They can help assess your dietary habits, evaluate your overall nutrient intake, and determine whether you need to adjust your supplementation. They may recommend reducing your intake of folic acid supplements or suggest alternative ways to meet your nutritional needs without exceeding safe limits.

In summary, while folic acid is essential for health, excessive intake, particularly from supplements, may be linked to cancer risk in certain populations. Monitoring your total folate intake and consulting with a healthcare professional can help ensure that you maintain a balanced approach to your nutrition without exceeding recommended levels.

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