Americans spend billions of dollars each year on dietary supplements, but experts argue there is no scientific proof that that any pill is a magic bullet.    

"Any claim to preventing disease or extending life with vitamin and mineral supplements are unproven," said Dr. George Blackburn from Beth Israel Deaconess Medical Center.    

Doctors prefer people get nutrition by eating vegetables, fruits and whole grains. But, Dr. Blackburn estimates only a quarter of Americans follow recommended guidelines.  For those who don't, a multi-vitamin may be just what the doctor orders.  

"I want them to take a low cost, simple, one a day vitamin and mineral supplement for insurance," Dr. Blackburn said.    

Pregnant women are advised to take pre-natal vitamins that contain extra folate.  With many fortified foods on the market, Dr. Blackburn has some reassuring advice for people worried about getting too many vitamins and minerals.    

"You would have to be taking a high dose, single supplement to worry about overdose," he said.

Anyone taking prescription medication should consult with their doctor about possible interactions with supplements.