150 million Americans take nutritional supplements daily.  That's according to the Council for Responsible Nutrition and the Nutrition Business Journal.   In fact, sales of supplements totaled $28 billion in  2010.  That's up more than $1 billion from the previous year.   And once January rolls around, sports nutrition and weight loss formulas start to fly off the shelves.

So, which supplements are right for you, and what's safe?  Registered dietician Erin Palinski explains dietary supplements are regulated by the federal government as a category of food. not as a drug. "Medications are tested and verified for potency and purity. with dietary  supplements, there is no testing standard, and that's where we can run into  issues."

Palinski says you need to be a savvy shopper and read labels and ingredient lists.  Those who are looking to build muscle and improve  performance often tout the benefits of protein, creatine, and CLA.  Though studies on creatine and CLA are mixed,  all three are generally considered safe if taken at  recommended levels.  "Even generally safe supplement ingredients, if you're taking them in too high  a dose, can be potentially dangerous," says Palinski.  She adds it can lead to things dehydration, increased risk for  kidney stones, and gastrointenstinal issues.

Palinski says one of the most popular supplements for athletes looking  to boost their energy is caffeine.  "In up to about 300mg per day, it may help increase athletic performance, but  above that amount we can run at the risk, since it's a stimulant, of increasing  blood pressure.  In very high amounts, it can actually lead to seizures."

Some fat-burning supplements, which contain a mix of  herbal ingredients, can also act as a stimulant. Are they effective?  There's no clear-cut answer but Dr. Taylor Wallace with the Council for Reasonable Nutrition  says you should always consult your doctor first. ""Long-term use of certain fat burners can have some very adverse events in  the liver."

Experts say you should keep an eye out for Ephedra, which has been banned by the Food and Drug Administration.  And check labels for something called Bitter Orange, also referred to as Synephrine.  It is similar to the main chemical in Ephedra and the government says there's little evidence it's any safer.

If you chose to use athletic or weight loss supplements, everyone agrees: watch where you buy and stick with reputable brands and retailers.  "If a claim for a dietary supplement is too good to be true, then it probably is," says Wallace.

When you are shopping for supplements, Palinski recommends looking for products that take part in the USP Dietary Supplement Verification Program.  A USP Seal means the product meets stringent, voluntary standards for safety and purity.