MADISON, Wis. -- We spend $4 billion a year on multivitamins, but according to Consumer Reports, not everyone needs one.

If you consistently eat a lot of fruits and vegetables, whole grains and dairy, along with low fat meat like chicken and fish, then you're probably getting most of what you need.

The problem, according to Consumer Reports, is that most people don't eat the recommended diet.

Not getting the nutrients you need can increase your risk of various diseases and disorders from the common cold to heart attack, stroke, mental decline, even some types of cancer.

A multivitamin can help fill some of the gaps in your diet. Consumer Reports testers recently evaluated 18 brands from discount and dollar stores.

What they found was that nearly half of the tested brands failed to contain their labeled level of at least one nutrient, and two of the vitamins failed to dissolve properly. That means your body won't absorb the nutrients.

Consumer Reports recommends steering clear of dollar stores when shopping for multivitamins. Inconsistent quality means you don't know what you're getting.

Instead choose big name brands, like Centrum and One A Day, or major store brands. These have done well in Consumer Reports tests.

Another tip, stick with a basic multivitamin.

There's really no need to pay extra for fancy add-ons such as herbs like ginkgo and ginseng, or phytochemicals such as lutein or lycopene.

Consumer Reports recommends avoiding mega-doses. In particular, too much vitamin C can cause gastrointestinal distress, excess iron can mask internal bleeding, and high levels of vitamin A increase the risk of liver damage and birth defects.

Most vitamins will keep for more than a year so you can wait for a sale and stock up when the price is low, according to Consumer Reports.

Visit Consumer Reports to find more information on how to choose the right multivitamin.