Four Vitamin Toxicities on a Gluten-Free Diet - Amy Burkhart, MD, RD (2024)

By Amy Burkhart MD, RD

Updated 2023

A gluten-free diet can lead to vitamin deficiencies. This is well known. But what about vitamin toxicities in a gluten-free dieter? Why would this happen?

Vitamin D, iron, B vitamins, calcium, zinc, copper, and vitamins A, E, and K. are often low on a gluten-free diet. But, many healthcare providers do not test for vitamin deficiencies. Because of this, people are taking it upon themselves to prevent the possibility of low vitamin levels. And they are often guessing how much to take.

Supplements are readily available over the counter. Many people are taking vitamins to prevent possible deficiencies, address persistent symptoms, or in these times, protect themselves against COVID-19.

Supplements can be beneficial, but they need to be used with caution.

Common culprits such as other food sensitivities or gluten exposure are evaluated when symptoms persist on a gluten-free diet. While these factors are often the cause and essential to consider, ongoing symptoms can result from someone’s treatment. That treatment often includes vitamins and supplements.

Below are four examples of vitamin toxicities I have seen most frequently in my practice. Remember, however, the potential for toxicity exists with any vitamins taken in supplementation.

Taking high doses of vitamin B6 for prolonged periods can lead to permanent nerve damage.

Vitamin B6 is a co-factor (helper) for many metabolic functions in the body. It is vital in maintaining health, but it can cause nerve destruction when taken at high doses for prolonged periods. If high blood levels are not addressed, the damage can be irreversible. Common symptoms of vitamin B6 toxicity include painful numbness and tingling of the hands and feet, ataxia (loss of coordination in body movement), painful skin lesions, nausea, heartburn, and photosensitivity.

Recommended doses vary, but suggested doses for adults range from 1-2mg daily. Many supplements contain much higher quantities—recommended amounts for a safe upper limit of normal range from 50mg-100 mg per day. If blood levels are high, all supplements containing vitamin B6 should be discontinued until levels return to normal.

Good food sources of vitamin B6 are whole grains, chickpeas, starchy vegetables such as potatoes, and organ meats. There are no reported cases of B6 toxicity from food sources.

Iron deficiency is common whether or not a person is on a gluten-free diet, but taking iron without appropriate monitoring can be dangerous.

Iron is essential for carrying oxygen in the blood. It is also needed for many enzymes and proteins to function. Although it is a crucial nutrient, the potential for iron toxicity is high because very little is excreted from the body. Symptoms of iron overload include joint pain, fatigue, weight loss, nausea, and stomach pain.

A widespread genetic condition called hemochromatosis occurs in 1% of the population. Most people with this condition do not know they have it. People with hemochromatosis are very efficient at absorbing iron. Iron accumulates in the body and deposits in body tissues and organs like the liver. I have seen several cases of hemochromatosis in the past few months. It is not rare. If someone with this condition takes iron supplements, they can quickly become iron toxic.

If iron levels are elevated, typically, stopping all iron is all that is needed. If the person has hemochromatosis, frequent blood draws ( a therapeutic phlebotomy process) may be required to get iron levels back to the normal range.

The recommended daily intake for adults is based on age and ranges from 8-18mg per day. Tolerated upper limits are 45mg per day. Supplementation beyond the daily recommended amount should be under medical supervision and not be undertaken without evaluating the baseline level.

Food sources of iron include liver, beef, chicken, fortified cereals, beans, lentils, spinach, and molasses.

Vitamin A is necessary for normal vision, organ and immune function, and reproduction. Toxicity can cause serious symptoms.

There are two forms of vitamin A:

– Preformed (animal sources and many supplements): In supplements, the preformed vitamin A is typically called retinyl acetate and retinyl palmitate.

– Provitamins (plant sources and some supplements): In supplements, this form of vitamin A is called beta carotene. Provitamins do not appear to be toxic but can turn the skin orange if ingested in very high amounts.

High intake of the preformed Vitamin A types is associated with toxicity and can cause nausea, dizziness, elevated intracranial pressure (pressure around the brain), headaches, coma, and death. High vitamin A levels during pregnancy are associated with congenital disabilities.

The recommended daily intake of vitamin A is 2300 IU for women and 3000 IU for men.

The recommended daily allowances differ during pregnancy and for children based on age.

The daily upper safe limits for Vitamin A are 2000 IU for infants, 3000-5000 IU for children (depending on age), and 10,000 IU per day for adults.

If levels are elevated, treatment typically consists of stopping all supplements. If someone has neurologic symptoms, additional treatments or medications may be required.

Food sources of preformed vitamin A are liver and fish oil, milk, and eggs. Good plant sources of vitamin A are sweet potato, spinach, carrots, and pumpkin.

Vitamin D has become a panacea, but high doses can work to our detriment. This vitamin is frequently used for COVID-19 prevention and often as a part of Coivid-19 treatment.

Vitamin D is essential for numerous body functions, including healthy bone formation, calcium regulation, and neuromuscular and immune function. It is also critical in minimizing inflammation.

It is present in very few foods unless they are fortified but produced by our bodies when exposed to sunlight. Due to the lack of dietary sources and minimal exposure to sunlight for many people, deficiency is common. That makes supplementing with vitamin D also common. This increases the risk of toxicity in the population because so many people take it.

Symptoms of toxicity are vague and include poor appetite, weight loss, irregular heart rhythms, and increased urination.

Recommended daily intake ranges from 400-600 IU per day, depending on age. Still, there has been a movement to shift that recommendation closer to 1000-2000 IU per day based on more recent findings.

Daily upper tolerable limits range from 1000 IU – 4000 IU per day, depending on age. Many patients require higher doses to maintain adequate serum levels, so monitoring is necessary.

If levels are unsafely elevated, stopping supplementation is all that is required.

Food sources of vitamin D include fortified products such as milk, cereals, and orange juice. Small amounts of vitamin D are found in beef liver and egg yolks.

A patient came to my office for chronic digestive symptoms. She was on a gluten-free diet for non-celiac gluten sensitivity. During her visit, she mentioned painful burning and numbness in her feet for about a year. As many people do, she had started herself on nutritional supplements to ensure she was getting adequate vitamins and minerals. She knew the gluten-free diet could be deficient in many nutrients, so she wanted to safeguard against any potential problems. What she didn’t realize, however, was that supplements could be toxic, even to those at risk of deficiency.

When her vitamin B6 level came back “too high to count,” we addressed the safe use of vitamins and supplements, an important topic for anyone taking nutritional supplements. We stopped all her vitamins that contained B6, and her levels came down. Her numbness and tingling resolved over several months. I hope her story and the following information makes you more aware of the caution to be taken with supplements. They can help improve health, but please use them with care and under the supervision of a health care practitioner.

This is just one example of how vitamins and supplements can cause vitamin toxicity. Supplements and vitamins are often needed, can be helpful, but please use them carefully and under the supervision of a knowledgeable provider.