For years, one of my patients took a daily high-dose vitamin B6 supplement at the recommendation of a naturopath. She trusted the scientific-looking genetic test he based this recommendation on, and never questioned whether she was actually deficient in vitamin B6 before buying and taking the expensive product, which contained a dose 3,800 percent of the daily recommended intake. After a few years, she started experiencing pain and tingling in her arms and legs, and finally sought care from a credentialed medical doctor. The diagnosis? Irreversible nerve damage ( neuropathy) caused by toxic levels of vitamin B6. To add insult to injury, she learned there was never a medical reason for her to have been taking vitamin B6 to begin with.
While my patient's story may not be typical among supplement users, it may be increasingly common as a result of the dangerous trend toward megadosing a variety of nutritional supplements -- both by mouth and intravenously -- for a variety of dubious reasons, generally at the recommendation of alternative health practitioners.
In recent years, a host of boutique laboratories have cropped up, offering official-looking blood tests, stool tests and genetic tests that cater to a cottage industry of expensive supplements pushed by chiropractors, naturopaths and so-called "functional medicine" nutritionists and doctors. Their blood tests commonly use non-standard definitions of what constitutes a normal blood level of vitamins and minerals, and often employ non-standard lab testing methods as well. As such, healthy people with adequate nutrition status by all evidence-based metrics may come out looking "deficient," and are prescribed extensive supplement regimens.
These labs also offer genetic tests that identify the presence of common variants in the human gene pool, which practitioners use to justify the sale of expensive, high-dose, specialized versions of vitamins B6 and B12 to people who show no clinical signs of a disorder or deficiency. (A favorite one is the MTHFR mutation.) This practice is carried out despite the absence of scientific evidence linking single copies of the MTHFR gene variant to the actual real-life health problems for which it is commonly blamed.
Another trend that places people at risk of toxicity from vitamins and minerals is the proliferation of so-called "infusion centers," where people spend a few hundred dollars per session to have various nutrients infused directly into their veins. The digestive system has some mechanisms to limit absorption of too-high nutrient doses taken by mouth. But when you pour nutrients directly into the veins, there's no gatekeeper mechanism to help protect you against overdosing. To be clear: There is no medically-justified reason for people who aren't hospitalized to require IV infusion of nutrients into their bloodstreams.
Fat-soluble vitamins -- vitamins A, D, E and K -- can be particularly toxic at high levels because our bodies store excess amounts of them rather than disposing of overages in the urine. Excessive vitamin A can lead to liver failure, and excessive vitamin E risks internal bleeding. Many minerals are also likely to be toxic at high levels -- some even fatally so. Too much iron can kill you. Too much iodine can damage your thyroid. Too much zinc can induce anemia from copper deficiency by out-competing it for absorption. Too much selenium can damage the joints and cause loss of hair and nails. Megadosing vitamins that are water soluble like vitamin C and many B vitamins may be generally less risky, but they're still not entirely risk-free: Excess vitamin C can cause kidney stones, and too much vitamin B6 can cause permanent nerve damage. Because dietary supplements are so laxly regulated, it's frighteningly common for products to contain accidental megadoses due to formulation errors.
There are a handful of medically-appropriate reasons for some people to take high doses of certain vitamins or minerals under specific circumstances. For example, people who malabsorb vitamin B12 in their guts as the result of an autoimmune condition or intestinal surgery may require a high dose of vitamin B12 (500 micrograms or 20,800 percent of the daily recommended intake) in a form that dissolves under the tongue; this is because only about 1 percent of that total dose can be absorbed through this channel. Sometimes, doctors will prescribe high-dose vitamin C as a laxative at doses of 2,000 milligrams -- or 3,333 percent of the daily recommended intake. High-dose niacin (vitamin B3) has been used to manage high cholesterol, though this has fallen out of favor due to its common, unpleasant side effect of facial flushing and a general lack of evidence for its efficacy. Doctors will also prescribe v itamin D, taken once per week at a high dose of 50,000 IUs, to help treat profound vitamin D deficiency, but this prescription typically only lasts for 12 weeks.
The National Academies of Science has established a safe upper range for most nutrients taken in supplement form based on scientific evidence. It's called the "Tolerable Upper Limit" and can be found online here. Before taking any supplements, it's a good idea to check this table and make sure the dose you're considering is underneath the upper limit; be sure to add up the total amount of a nutrient you're taking if you use multiple dietary supplements with overlapping vitamins and minerals, such as a multivitamin in addition to a separate B-complex pill. If anyone recommends that you take a daily vitamin or mineral supplement with a dose over the Tolerable Upper Limit, seek a second opinion. If you opt to proceed, make sure the provider is monitoring your blood levels of that nutrient every few months to make sure they stay in a healthy range.
So many of my patients have sought care from alternative health practitioners due to mistrust of conventional Western medicine. They have a perception that medical doctors just want to treat everything with pharmaceuticals rather than addressing a problem's underlying cause or considering changes in diet or lifestyle before resorting to drugs. There's certainly a lot of legitimacy in this critique. But where is the equal skepticism of those who profit from selling extensive vitamin and mineral supplement regimens, which include barely-regulated pills, often by the dozens, at unnaturally high doses? Vitamins and minerals may seem more "natural" than drugs sold by big pharmaceutical companies, but that certainly doesn't make them unequivocally safe. Buyer beware.
Tamara Duker Freuman, MS, RD, CDN, is a registered dietitian whose NYC-based clinical practice specializes in digestive disorders, celiac Disease, and food intolerances. Her personal blog, www.tamaraduker.com, focuses on healthy eating and gluten-free living.