How to make your vitamin intake more effective

There are more than 90,000 vitamins and supplements on the market 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 all these 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 many experts 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, who is a registered dietitian.

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

Registered dietitian Whitney Linsenmeyer explains the science behind that strategy.

"Those fat-soluble vitamins will be better absorbed with a meal that contains at least 10 grams of fat or more," Linsenmeyer said.

One study shows taking vitamin D with a high-fat meal increases 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 experts say it's best to take those separately.

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

That's why 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 explained.

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

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

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.