Tips to make vitamins work better

ST. LOUIS – With more than 90,000 supplements on the market, the vitamin industry is a big one in the United States. 

Since 1999, the National Institutes of Health has spent $2.4 billion researching vitamins and minerals. 

The jury is still out on how effective the supplements are, but there are steps consumers can take to optimize the efficacy of their vitamins. 

Fifty percent of adults take vitamins and supplements, but dietitians say we're not getting the most bang for our buck.  

"There are ways to enhance the absorption, the efficiency of the vitamin and mineral supplement," said Moe Schlachter, a registered dietitian at Houston Family Nutrition.

One way to do that? Take fat-soluble vitamins like A, D, E and K with a high-fat meal. 

"Those fat-soluble vitamins will be better absorbed with a meal that contains at least 10 grams of fat or more," said Whitney Linsenmeyer, registered dietitian at Saint Louis University in St. Louis.

One study showed taking vitamin D with a high-fat meal increased absorption 32 percent more than with a fat-free meal. 

"Some nutrients will enhance the absorption of others, and then some nutrients will inhibit the absorption of others," Linsenmeyer said.

Vitamin D increases the absorption of calcium, so take those together. Calcium and zinc both inhibit iron absorption, so it's best to take those separately. 

"Caffeine can also inhibit absorption of certain nutrients," Schlachter said.

People should avoid taking iron with coffee. Most vitamins with the exception of iron should be taken with food. 

"When we're consuming these with foods, we also have those gastric juices and enzymes present that are helping us to absorb those nutrients optimally," Linsenmeyer said.

Remember that all vitamins are not created equal. To ensure you're getting safe, high-quality vitamins, always look for the U.S. Pharmacopeia seal. 

"The USP is really the saving grace, I would say, in the world of supplements," Schlachter said.

With $30 billion spent every year on dietary supplements, a little vitamin savvy can go a long way. 

It's important to note that some vitamins and supplements can build up to toxic levels if you take too much of them, especially fat-soluble vitamins like A, D, E and K. 

Some vitamins can also interfere with medications prescribed by your doctor, so it's important to let your doctor know about any supplement you take.