REVEALED: The common supplements experts say you should avoid - including one that's now linked to BRAIN CANCER...

We're a nation of pill poppers - so it's no surprise vitamins and supplements have become a $50billion-a-year industry.

An estimated 70 percent of American's take some form of a supplement each day.

But doctors caution that not only are a huge number of the products duds, they might actually harm rather than boost your health. 

A new study suggested that taking nicotinamide riboside (NR), a form of the vitamin b3, might increase your risk of developing aggressive forms of cancer. 

The 70-cent tablets are touted for it's anti-aging properties and have gained rampant popularity in recent years among wellness influencers. 

The study, led by Elena Goun, a chemistry professor from the University of Missouri, discovered that the popular supplement might help cancer spread. 

NR has been shown to support cell growth. When Professor Goun fed it to cancer cells in the lab, she found they were able to use it as a potent fuel to spread across the body. 

This, the study said, could increase peoples risk of developing hard-to-treat forms of breast cancer and increase the risk that the disease will spread to the brain and other parts of the body.

However, the study authors caution, finding this link doesn't definitely mean that these supplements cause cancer - people might need to take in a lot of the supplement for it to have a serious effect on their body, for example.

It does shine light on how unregulated the supplement industry is, and how little we know about the long term effects of many supplements, Professor Goun said.  

'Some people take them [vitamins and supplements] because they automatically assume that vitamins and supplements only have positive health benefits, but very little is known about how they actually work,' she said. 

This isn't the only supplement that has been linked to unfortunate outcomes. 

A review of 450,000 Americans by researchers from Johns Hopkins University found that multivitamins did nothing to reduce the risk of heart disease or cancer. 

'Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided,' the study authors wrote. 

Taking too much Vitamin E has been associated with an earlier death overall and prostate cancer, according to Mayo Clinic. 

And studies suggest beta carotene, a supplement that is naturally found in vegetables, may increase your risk for developing lung cancer if you were previously a smoker. 

However, all of these studies note that this link isn't proven conclusively, and that you're probably not in immediate danger if you're currently taking these supplements.  

Meanwhile, supplements for sexual performance, weight loss, sports performance and cognitive enhancement are usually the most problematic categories, Dr Pieter Cohen, an internist from Harvard University Medical School told Discover. 

'These health claims do not need to be supported by evidence in human trials. In other words, it can say things like this will improve your cognition or improve your memory, even if there's no study that's ever shown that the supplement will actually help you do that,' he said. 

For example, Gwenyth Patltrow's company Goop manufactures a product called 'Brain Boost daily chews', which are supposed to 'support energy and focus'. Cohen said products like these don't have scientific basis.  

Cohen explained further that the supplements in these categories are most likely to contain harmful substances, experimental drugs or far less or more of the ingredients they're supposed to contain. 

 Cohen, who is part of a lab that tests supplements for their veracity, said that in a study of a brand of sleep gummies, his company found incredibly high levels of CBD. 

Other studies have found that supplements are frequently contaminated with cancer-causing heavy metals. 

Another study yet found that all of the 138 supplements tested contained foreign bacterium. 

This can happen because supplements fall into category somewhere into a no-mans-land between a drug and a food item, which means that the FDA does not regulate them. 

So, the only way you can know if a product actually contains what it says on the label is if the company opts to go through third party testing.

Some third party testing companies have stamps that you can look out for on the label of bottles, like US Pharmacopeia. If you see that a bottle has a gold and green stamp emblazoned with USP on it, it's a sign that it's been verified. 

'When it’s also third-party certified, that’s the most likely way of getting what you think you are in the bottle,' Cohen said. 

In one of Cohen's tests, he discovered that a brand of sleep vitamins contained 346 percent more melatonin than it stated on the label. An overdose of the supplement is rarely fatal, but can cause tremors, nausea , confusion, drowsiness and anxiety. 

 'Sometimes what's in the bottle can be very worrisome,' Cohen said. 

Another problem with supplements is that sometimes your body doesn't need more of a particular nutrient. For example, taking in too much Vitamin A can cause headaches, dizziness and hair loss.  

One of the other murky areas you can run into with supplements is how they interact with other drugs you may be taking. 

For example, St John's Wort has been shown to block or minimize the effects of statin's, a class of drugs that help lower cholesterol. 

Also, NR supplements have been shown to lower blood pressure, so people taking medication for blood pressure could enter dangerous territory if they take the supplements on top of it.

Another popular herbal supplement called Ashwagandha can alter the effects of diabetes medication, sending people with the condition into dangerously low blood sugar territory. 

If you consult your doctor before you start any new supplement, you will probably be safe from the deleterious effects, Dr. Eve Glazier and Dr Elizabeth Ko from UCLA wrote. 

'When someone wants to start taking a supplement, it is always wise to check in with their doctor.'

Further, most people don't need to be taking supplements at all, Cohen said. The best way to get daily nutrients is from eating a well rounded diet, Michelle Routhenstein, a registered dietitian, previously told the Daily Mail.