You may be tempted to take prenatal vitamins because of unproven claims that they promote thicker hair and stronger nails. However, if you're not pregnant and not planning to become pregnant, high levels of certain nutrients over a long period of time may actually be more harmful than helpful.

Prenatal vitamins are formulated specifically for women who are pregnant or trying to become pregnant, and women who are breast-feeding, with particular emphasis on:

• Folic acid. To reduce the risk of having a child with neural tube defects, it's recommended that women who are trying to become pregnant get 400 to 800 micrograms (mcg) of folate or folic acid a day through diet and supplements. Other healthy adults — both men and women — need only 400 mcg a day. While uncommon, getting too much folic acid by taking supplements can mask the symptoms of vitamin B-12 deficiency and delay diagnosis and treatment.
• Iron. During pregnancy, the recommended intake of iron is 27 milligrams (mg) a day. Women between the ages of 19 and 50 who aren't pregnant need only 18 mg a day, and women age 51 and older and all adult men need only 8 mg a day. Getting too much iron can be toxic because it can build up in your body, causing constipation, nausea, vomiting, diarrhea and, in severe cases, possibly death.
• Calcium. Pregnant adult women and healthy men and women ages 19 to 50 all need 1,000 mg a day. Men and women age 51 and older need 1,000 mg a day and 1,200 mg a day, respectively. Because prenatal vitamins are intended to supplement calcium you get in your diet, they generally contain only 200 to 300 mg of calcium. If you rely on prenatal vitamins to meet your calcium needs, you likely won't get enough, raising your risk of osteoporosis and other health problems.

Generally, if you eat a healthy, balanced diet, taking multivitamins of any sort isn't necessary.