Increasing the number of prenatal vitamins that you take each day or taking folic acid in amounts greater than 400 mcg per day without a physician's supervision is inadvisable. At the higher doses, it is possible that folate supplementation may mask the presence of a vitamin B12 deficiency and result in neurological problems for the mother; therefore, take 400 mcg daily unless asked to take more by a physician who will provide appropriate evaluation and follow-up.
When looking for a good vitamin, your doctor can guide you to the right mix of nutrients for you. Remember that more isn't always better. In a study of over 22,000 pregnant women, those who took supplements with more than 10,000 international units (IU) a day of pre-formed vitamin A (retinol) were almost five times more likely to give birth to a baby with a birth defect than women who consumed 5,000 IU or less. (A good vitamin A alternative is beta-carotene, which the body will convert into vitamin only if needed. These days, many supplements have beta-carotene added to its formula but list it under Vitamin A activity.)
When Should I Be Taking Folic Acid?
In Western countries, the only vitamin really lacking in women's diets is folic acid. Birth control pills accentuate a woman's vitamin B9 (folate) deficit, and may also contribute to a vitamin B6 deficiency. So supplementing even when you are not trying to get pregnant is a good idea. The March of Dimes and the Centers for Disease Control (CDC) recommend that all women of child-bearing age get 400 micrograms (0.4 mg) of folic acid daily. This is especially wise if you are sexually active, in case you get pregnant unintentionally.
If you are planning to start or build your family, start taking prenatal vitamins at least two months before conception. A good prenatal vitamin should include folic acid and calcium among other nutrients that are important to a healthy pregnancy and baby. Research has shown that taking folic acid can reduce the occurrence of birth defects in the spine, skull, and brain (NTDs) by 50 to 70 percent.
Take folic acid daily. Because it is a water-soluble vitamin, is not stored in your body in significant quantities, and any excess is excreted in the urine.