Unless you eat a perfectly balanced diet and soak up plenty of sunshine, you might need a diet supplement. But before dropping dough on a bottle of pills, it's best to determine if you really need them by checking with a doctor. Here's what science has to say about some of the most common supplements.
Cost: $7 for 75
Claim: Makes up for nutritional inadequacies and improves overall health.
What experts say: In people with very poor nutrition, multivitamins can reduce the risk of certain cancers, but there really isn't any evidence that multivitamins prevent chronic disease. Although they are not necessary for most people, multivitamins can help cover nutritional deficits, they're relatively inexpensive, and they cast a pretty broad and basic net.
Cost: $6 for 100
Claim: Boosts bone health and the immune system.
What experts say: Vitamin D supplementation is necessary only for people who are deficient, as indicated by lab work. Too much can be harmful, and humans can manufacture vitamin D, for free, from sunlight exposure.
Cost: $26 for 130
Claim: Reduces the risk of heart disease.
What experts say: Foods high in omega-3 fatty acids, such as fatty fish, are beneficial, but studies on supplements have been inconsistent and haven't shown the same benefits.
Cost: $5 for 250
Claim: Reduces neural-tube defects in babies.
What experts say: Women of childbearing age should supplement daily with folic acid even if they aren't planning pregnancy. Folic acid is generally present in most multivitamins -- check the labels.
Cost: $11 for 120
Claim: Boosts bone health and fracture prevention in older adults.
What experts say: Studies haven't shown that calcium supplementation results in fewer fractures in the older population, although taking calcium in combination with vitamin D may be beneficial.
Cost: $8 for 100
Claim: Reduces the chance of some cancers.
What experts say: While research results have been inconsistent, eating foods naturally high in vitamin C may help lower cancer risk. Supplements, however, do not show the same effect and probably aren't necessary.
Cost: $5 for 30
Claim: Reduces the risk of cardiovascular disease.
What experts say: Some research shows that CoQ10 may benefit those who already have heart disease, but the jury is out on whether there is any benefit to those who do not.
Cost: $11 for 100
Claim: Helps with certain types of anemia and reduces the risk of heart disease.
What experts say: B12 has been shown to lower homocysteine levels in certain populations (people with heart disease often have high homocysteine levels), but there is a lack of evidence that it actually helps prevent heart disease. Supplements are recommended for those who are B12 anemic.
Cost: $16 for 30
Claim: Helps restore normal intestinal function.
What experts say: Evidence suggests that certain probiotics can help prevent diarrhea in people taking antibiotics and also help those with irritable bowel disease. But there isn't enough evidence to recommend daily use.
Cost: $35 for 120
Claim: Helps with the pain of osteoarthritis.
What experts say: The American College of Rheumatology recommends against use in people with hip or knee osteoarthritis. There hasn't been enough research on other joints to draw a conclusion. Bottom line: Save your money.
Cost: $4 for 100
Claim: Helps prevent heart problems.
What experts say: Some studies have shown a positive correlation, but others, particularly with people at higher risk of heart disease, showed no difference between people who took it and those who did not.