But, CBS News Correspondent Medical Correspondent Dr. Jennifer Ashton points out, those aren't good places to keep them.
It turns out, according to a Purdue University study, that both kitchens and bathrooms are hotbeds for high humidity conditions that could hasten the degrading of the vitamins and other health supplements, even if the bottle lids are on tight.
Ashton notes that kitchens, from stoves and dishwashers, and bathrooms, from showers, are high in heat and humidity. The latter causes the water-soluble solids to dissolve, which could cause chemical changes in vitamins such as Vitamin C. That decreases the quality and shelf-life of the product, and could mean you're not getting the all the nutrition you thought you were.
Special Section: Dr. Jennifer Ashton
So, says Ashton, store products in dry conditions, out of areas that are humid. If you open and close a vitamin bottle, say, in the bathroom, a little bit of moisture gets trapped in there each time. Keep it away from direct sunlight. Finally, it's very important to keep them away from your children's reach. Excessive amounts of vitamins can be harmful. You can put them in an airtight container in a dry area of your home, like a linen closet. If you're buying these vitamins in bulk, it's important to remember that, so all the money you save isn't wasted!
Also, contrary to popular belief, refrigeration can also degrade the vitamins.
According to the researchers, to tell if vitamins are or are going bad, look for liquid in any containers -- and if there are brown spots on the vitamins, throw them away. The FDA doesn't require supplement makers to print expiration dates, but some vitamin makers do include use-by-dates.
Taking vitamins that have lost their potency won't harm you -- they don't turn poisonous. You just won't get the intended amount of vitamins, and may have to take more.
Are vitamin supplements even necessary?
Ashton says a balanced diet of whole fruits and vegetables should be able to provide the nutrients you need. There's also been controversy about how well vitamins work in fighting disease. A study from last year from the Women's Health Initiative found that women who took multivitamins were just as likely to be diagnosed with cancers or heart disease as those who didn't. Another recent study found that Vitamin E and selenium didn't prevent prostate cancer. A doctor may recommend extra vitamins if the patient is vegetarian or vegan, or if a woman is pregnant or breastfeeding, or if blood tests show him or her to be low in a particular vitamin.