Nearly 40 percent of American adults take a daily vitamin and collectively spend some $5 billion on multivitamins each year.

A recent survey by Consumer Reports revealed confusion about which are the best vitamins and concerns about contamination.

The magazine studied 21 regular daily multivitamins, as well ones for seniors and chewables for children, to find some answers.

"Not everyone needs to take a multivitamin, particularly if you eat a balanced diet. But it's necessary for pregnant women and people on strict diets," Gayle Williams, with Consumer Reports, said.

An outside lab tested multivitamins for contamination and to see if they actually contained the ingredients that their manufacturers claim.

None of the vitamins contained worrisome levels of heavy metals or excessive doses of any vitamin or mineral.

Consumer Reports also tested to see how well the multivitamins dissolve, which is important to getting all the nutrients from a vitamin.

Two of the most expensive multivitamins – Rite Aid's Whole Source Mature Adult and Vitamin Shoppe's One Daily – did not dissolve sufficiently.

Samples from two of three lots of Vitamin Shoppe's One Daily contained only 73 percent of the vitamin A listed.

"The good news is all the other multivitamins passed Consumer Reports' tests, so you can chose by price," Williams said.

Walmart's Equate brand has some of the least expensive multivitamins and vitamins for seniors and children. Costco's Kirkland Signature multivitamins cost even less.

To cut costs, look for sales and buy in bulk then, because many vitamins don't expire for at least a year.