We Need to Talk About Megadosing

RDN Liz Shaw (@shawsimpleswaps) gives us the lowdown on this troubling phenomenon.

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In the past year, we’ve seen the rise of a troubling trend: megadosing vitamins without medical supervision. In simple terms, people are taking vitamins doses that are sometimes 10 to 20 times above the recommended dietary allowance, or RDA. But when it comes to taking vitamins, more is rarely better, especially without the recommendation and supervision of a medical professional. 

Conventional wisdom says that any excess amounts would simply be metabolized by the body, especially water-soluble vitamins like vitamin C. But the truth is that nutritional science is a complicated subject. It’s hard to evaluate the exact impact of a single nutrient outside of the larger context of a person’s diet, health condition, genetic makeup, activity levels and more. 

What’s more, nutrition has a cumulative effect over a person’s life. There can be unforeseen consequences of megadosing, even for vitamins that were previously thought to be harmless in large quantities. A study in the August 2017 issue of the Journal of Clinical Oncology suggested that taking B6 and B12 supplements in high doses appeared to triple, almost quadruple, the risk of lung cancer in some people.

The risk of lung cancer for men who took 20 milligrams of B6 daily for years was twice as high compared to men who didn’t. For smokers, the effect appeared to be even more dramatic—the lung-cancer risk increased threefold. Smokers who supplemented B12, more than 55 micrograms daily, had almost four times the risk!

The RDA in the United States is 1.7 milligrams a day for B6 and 2.4 micrograms for B12. Men in the high-risk group were taking about 20 times these amounts. This sounds like an absurdly high dose—except that supplements containing these types of doses are mainstream and available at grocery stores and pharmacies.

To uncover the risks of this trend, we interviewed registered dietitian Elizabeth Shaw, MS, RDN, CLT. Shaw is an author, nutrition consultant and founder of She offers her observations on the trend and discoveries from her own clinical practice.

Have you seen this megadosing trend in your practice as a dietitian?

Yes, unfortunately I have. It’s amazing to me that individuals will read one thing on the internet one morning and then within hours have their order placed for the supplement to arrive via Amazon Prime in a day! While I appreciate the active interest in one to take care of their health, my concern as an RDN arises when individuals aren’t properly supervised by a medical professional.

For instance, when it comes to vitamin D, there is what we call an “upper limit” that should not be exceeded due to adverse health outcomes in most individuals. For adults, that number is 4,000 IU/day of vitamin D. Intakes above this number can result in toxicity, which results when amounts in the blood become too high.

Signs include nausea, vomiting, poor appetite, constipation, weakness, and weight loss. Furthermore, through the action of raising blood levels of calcium, too much vitamin D can cause confusion, disorientation, and problems with heart rhythm. Lastly, high amounts of vitamin D can also cause harm to the kidneys. 

What substances are most commonly megadosed?

Honestly this question is so varied for such a wide audience. For instance, I’ve found that many of my male students who participate in strength training and other fitness activities consume large doses of creatine. While creatine may be viewed as safe in the correct dosage, the effects of the dosing on the younger populations development are still not well studied. Thus, I recommend my clients work directly with a registered dietitian on finding the eating regimen that works for them to help achieve their personal goals.

Omega-3 supplements are often taken in large quantities too, but I usually find this is done under the supervision of a medical professional to help with heart health for those at risk of cardiovascular events. I too take an omega-3 supplement in proper quantities because I don’t meet my daily needs through diet alone! This is important to remember because sometimes supplements can serve as a great vehicle to help meet those needs in an appropriate quantity when diet is not providing enough of the nutrient on its own.

What are your thoughts on the super-high doses often seen in very mainstream supplements?

My hope is that the clickbait for consumers and companies for that matter to engage in megadosing will subside for the general population and be recommended only in those cases that truly warrants an exceptional high dose. I know it’s far-fetched, but my hope is that health care professionals can work with the media and supplement companies to help them understand the importance of providing a product that meets individuals needs without putting them at adverse health conditions related to exceeding an upper limit for a particular vitamin.

What would you advise for your clients to consider when they're choosing supplements?

First and foremost, make sure you’ve had a recent workup with your physician to assess your overall health. Since low vitamin D is a big concern these days, often times insurance will cover testing. Once you’ve received your results or spoken with your physician or dietitian about your current dietary habits and nutritional needs, ask them for their suggested brands.

If a health care professional is contracted with a particular company, they need to disclose this to you. I always recommend two brands to my clients to give them options so they can find what works with their budget and body, since everyone will respond so differently.

What are some legitimate scenarios for megadosing? We know that those with blood serum levels of extremely low vitamin D will be prescribed megadoses by their doctors. Some substances like omega-3 fatty acids don’t have established RDAs.

Given that individual needs will vary, it’s most important to speak with your physician before considering increasing one’s intake of a supplement to that over the recommended dietary allowances. 

With that said, I’ve spoken to patients who have been referred by their physicians to take higher doses of omega-3s to aid in cardiovascular health as a result of adverse events such as an myocardial infarction (MI).

While there is currently no upper limit for omega-3s, some studies have reported side effects with excessive consumption. Here’s the exact information from the NIH:

"The IOM did not establish a UL for any omega-3s, although it noted that high doses of DHA and/or EPA (900 mg/day of EPA plus 600 mg/day DHA or more for several weeks) might reduce immune function due to suppression of inflammatory responses. However, according to the European Food Safety Authority, long-term consumption of EPA and DHA supplements at combined doses of up to about 5 g/day appears to be safe. It noted that these doses have not been shown to cause bleeding problems or affect immune function, glucose homeostasis, or lipid peroxidation. The FDA recommends not exceeding 3 g/day EPA and DHA combined, with up to 2 g/day from dietary supplements. Some doses used in clinical trials exceed these levels. Commonly reported side effects of omega-3 supplements are usually mild."

Lastly, I read an interesting article that chatted about the mega-dosing seen with vitamin C as an antioxidant with cancer. From what the research alludes to, the intravenous administration of the vitamin is what they’ve found to have the effects, so it’s not necessarily recommended to just pop a vitamin C pill for patients who are battling cancer.

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Elizabeth "Liz" Shaw MS, RDN, CLT, CPT is a San Diego-based registered dietitian, food blogger, author and wellness coach. Her work has appeared in Huffington Post, Bustle, Shape Magazine and CW San Diego.

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