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A new study revealed that many over-the-counter vitamin D supplements might not actually contain what their label says.

The study found that while some vitamin D supplements contain a lot more vitamin D than listed on the label, others contain significantly less, according to a new study published Feb. 11 in the journal JAMA Internal Medicine.

However, researchers are more worried supplements delivering too little vitamin D than vitamins that provide too much.

Researchers said that while it's hard to overdose on vitamin D, people who are receiving too little could face potential health risks like osteoporosis, heart disease and cancer.

Vitamin D is also called the "sunshine vitamin" because the body produces it when it is exposed to natural sunlight. The vitamin is frequently added to milk and other foods and is also available in small doses in fatty fish, cheese and egg yolk. However, researchers say that it can still be difficult for people to get the vitamin needed through diet, so doctors sometimes recommend that people take supplements.

Recently, health experts have disagreed on how much vitamin D people need.  However, the Institute of Medicine, an American non-profit, non-governmental organization, recommends that teens and adults take 600 international units (IU) a day and older adults over the age of 70 take 800 IU a day.

In the latest study, researchers analyzed the content of 55 over-the-counter bottles of vitamin D supplements from 12 unidentified manufacturers. Researchers also tested vitamin D pills produced at compounding pharmacy that makes individualized drugs.

The findings reveal that the amount of vitamin D found in the supplements ranged from 9 percent to 146 percent of the amount stated on the label. Furthermore, when researchers tested five pills from the same bottle, the pills had ranged from 52 percent to 135 percent of the amount listed on the label. Researchers noted that when the five pills were averaged out, two thirds were within the state range.

"We were surprised by the variation in potency among these vitamin D pills," lead author Dr. Erin S. LeBlanc of the Kaiser Permanente Center for Health Research in Portland, Oregon, said in a statement. "The biggest worry is for someone who has low levels of vitamin D in their blood. If they are consistently taking a supplement with little vitamin D in it, they could face health risks."

While the supplement industry remains largely unregulated, the study found that manufacturers who volunteer to have the quality of the supplements tested by the U.S. Pharmacopeial Convention, an independent, nonprofit organization that sets public standards for the quality of dietary supplements, may be more accurate in their vitamin dosages.

LeBlanc and her team tested one supplement from a USP Verified manufacturer in their sample and found that the amount of vitamin D in pills from that bottle was on average more accurate than the other bottles tested in the study.

"The USP verification mark may give consumers some reassurance that the amount of vitamin D in those pills is close to the amount listed on the label," LeBlanc said. "There are not many manufacturers that have the USP mark, but it may be worth the extra effort to look for it."