葉酸過多的 4 種潛在副作用

How does too much folic acid form?

Your body does not absorb folic acid as easily as folic acid.

It is estimated that about 85% of the folate in fortified foods or supplements is absorbed, while only 50% of the naturally occurring folate in food is used by your body.

After folic acid is absorbed into the blood, it is broken down into smaller compounds by the liver. However, the liver can only process a certain amount of folate at a time .

Therefore, consuming too much folate from fortified foods and supplements can cause unmetabolized folate (UMFA) to accumulate in the blood. This doesn't happen when you eat foods high in folate.

This is concerning because high blood levels of UMFA appear to be linked to various health problems.

Dietary Folate Equivalents Because folate is more readily absorbed than folate found in food, the Food and Nutrition Board (FNB) of the National Academies of Sciences, Engineering, and Medicine developed dietary folate equivalents (DFE) to develop more specific folate intake recommendations. (1Trusted Source).

1 microgram of DFE is equal to:

  • 1 microgram of folate in food
  • 0.6 mcg folic acid from fortified foods or dietary supplements taken with food
  • Take 0.5 mcg of folic acid from a dietary supplement on an empty stomach

There is no upper limit (UL) set for naturally occurring folic acid in foods.

However, the National Institutes of Health (NIH) recommends that adults over 19 years of age limit their intake of folic acid from fortified foods and supplements to 1,000 micrograms per day. The UL for children is even lower, ranging from 300-800 micrograms depending on age .

Keep in mind that most people don't get more than 1,000 mcg of folate per day unless they take a high-dose supplement.

In fact, according to the NIH, it is estimated that only about 5% of men and women ages 51-70 consume more than this amount each day, primarily due to the use of supplements.

1. Can mask vitamin B12 deficiency

High folate intake may mask vitamin B12 deficiency.

Your body uses vitamin B12 to make red blood cells and keep your heart, brain, and nervous system functioning optimally.

If left untreated, vitamin B12 deficiency can cause irreversible neurological damage, making delayed diagnosis particularly worrisome.

Your body uses folate and vitamin B12 similarly, which means deficiencies in both can cause similar symptoms.

Therefore, folic acid supplementation may mask vitamin B12-induced megaloblastic anemia and allow underlying vitamin B12 deficiency to go undetected.

Megaloblastic anemia is a disease characterized by enlarged red blood cells. It may cause symptoms such as weakness, fatigue, difficulty concentrating, and shortness of breath.

If you take folic acid supplements and notice any of these symptoms, consider getting your B12 levels checked.

2. May accelerate age-related mental decline

Too much folic acid may accelerate age-related mental decline, especially in people with low vitamin B12 levels.

One study of people over 60 showed that high blood levels of folate, or UMFA, were associated with reduced intelligence in people with low vitamin B12 levels. This association was not found in people with normal vitamin B12 levels.

Another study showed that people with high folate and low vitamin B12 levels were 3.5 times more likely to experience loss of brain function than those with normal blood parameters.

However, keep in mind that more research is needed to confirm that supplementing with large amounts of folic acid may be detrimental to mental health.

3. May slow down children’s brain development

Adequate folic acid intake during pregnancy is necessary for your baby's brain development. It may also reduce the risk of birth defects.

Because many women cannot meet their folic acid needs through food sources alone, women of childbearing age are often encouraged to take folic acid supplements.

However, taking too much folic acid during pregnancy may increase insulin resistance and slow brain development in children.

In one study, 4- and 5-year-old children born to mothers who supplemented with more than 1,000 mcg of folic acid per day during pregnancy scored lower on brain development tests than those born to mothers who supplemented with 400-999 mcg of folic acid per day.

Another study showed that higher blood folate levels during pregnancy were associated with a higher risk of insulin resistance in children aged 9 to 13 years.

Although further research is needed, it is best to avoid taking folic acid supplements above the recommended daily dose of 600 mcg during pregnancy unless otherwise advised by a health professional.

4. May increase the likelihood of cancer recurrence

The role of folate in cancer development and recurrence appears to be twofold.

Research shows that exposing healthy cells to adequate levels of folate can protect them from cancer. However, exposing cancer cells to high levels of folate may help them grow or spread.

Still, research results are mixed. While some studies point to a slightly increased risk of cancer in people who take folic acid supplements, most studies have not found a link.

Presumably, the risk may depend on the type of cancer and your health history.

For example, some earlier studies have shown that people previously diagnosed with prostate or colorectal cancer who supplemented with more than 1,000 mcg of folic acid per day had a 1.7-6.4% increased risk of cancer recurrence.

Still, eating lots of folate-rich foods doesn't appear to increase cancer risk. It might even reduce it.

Ultimately, more research is needed on the potential association between folic acid, folic acid supplements, and cancer risk and recurrence.

Recommended uses, dosage and possible interactions

Most multivitamins, prenatal supplements, and B vitamins contain folic acid, but it is also sold as a supplement. In some countries, some foods are also fortified with vitamins.

Folic acid supplementation is often recommended to prevent or treat low blood folate levels. Additionally, people who are pregnant or planning to become pregnant often take them to reduce the risk of birth defects.

The recommended dietary allowance (RDA) for folic acid is 400 micrograms for people over 14 years of age. People who are pregnant and breastfeeding should take 600 and 500 micrograms respectively. Supplement dosage is usually 400–800 mcg.

You can buy folic acid supplements without a prescription. They are generally considered safe when taken in normal doses.

That said, they can interact with some prescription medications, including some used to treat epilepsy, rheumatoid arthritis, and parasitic infections. Therefore, if you are taking other medications, it is best to consult a health professional before using folic acid supplements.

generalize

Folic acid supplements are generally safe and a convenient way to maintain adequate folate levels.

However, consuming too much folic acid may cause some side effects, including slower brain development in children and accelerated mental decline in older adults.

While further research is needed, you can work with your health care professional to determine your folate levels and whether you need to take supplements.

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