Vegan diets raise concerns for iodine deficiency

A new study comparing a vegan diet with a mixed diet has found no difference in vitamin B12 levels. However, one-third of the vegan participants were iodine-deficient.

There are many benefits to a vegan diet, including a lower risk of heart disease, cancer, and type 2 diabetes.

However, a growing concern is the lack of dietary nutrients that are mainly present in animal foods. Two important nutrients are vitamin B12 and iodine.

Vitamin B12 is essential to the body

Vitamin B12, also known as cobalamin, helps the body form nerves, red blood cells, and DNA. Maintaining adequate vitamin B12 levels is also crucial for cell metabolism and supporting the nervous system.

According to the National Institutes of Health (NIH), the average adult needs about 2.4 micrograms (mcg) of vitamin B12. The only natural sources of vitamin B12 are animal-based. They include various types of meats and fish, as well as dairy products, clams, and eggs.

As vitamin B12 does not occur naturally in plant-based foods, those eating only these foods are at risk for vitamin B12 deficiency. A 2017 study in the journal Nutrients found that 69.9% of males and 83.4% of females who were under the age of 55 years and identified as vegan lacked sufficient vitamin B12.

Since vitamin B12 is vital in making red blood cells, insufficient levels can increase the risk of anemia. Also, without vitamin B12, the brain cannot function correctly, which can lead to cognitive impairments. There is also evidence of a link between this vitamin deficiency and depression, Alzheimer’s, Parkinson’s disease, and dementia.

Importance of iodine in the diet

Iodine is another essential nutrient for the body. Iodine is crucial to making thyroid hormones, and the recommended intake for an adult is 150 mcg. However, about 38% of the world’s population lack adequate iodine levels.

Iodine is in fish, eggs, and dairy products. Unlike vitamin B12, iodine is naturally available to vegans in seaweed.

Despite some natural sources, getting sufficient iodine can still be challenging for vegans. A 2011 study in The Journal of Clinical Endocrinology & Metabolism found vegans to be at high risk for iodine deficiency.

Low iodine levels can force the thyroid to absorb iodine from the blood, which may lead to hypothyroidism. Iodine deficiency during pregnancy or in young children may also impair cognitive development and increase the risk of intellectual disabilities.

A growing trend for vegan diets

Despite the nutritional concerns, eating plant-based foods remains increasingly popular. For instance, a 2017 study in the Journal of Nutrition Education and Behavior found that in 2012, 1.9% of people in the U.S. followed a vegan or vegetarian diet for health reasons. This was an 18.8% increase from 2002.

In response to the rising interest in veganism, researchers at the German Federal Institute for Risk Assessment sought to find any updates regarding the average vegan’s nutritional health.

The study appears in the journal Deutsches Ärzteblatt.

Study design

The researchers selected a total of 72 participants aged 30–57 years from Berlin, of whom 36 were vegan, and 36 were eating an omnivorous diet consisting of both plant and animal foods.

The team used questionnaires to collect demographic information from these individuals, including their age, education level, and lifestyle factors.

Using the German Nutrient Database, the researchers used a 3-day dietary protocol to measure nutrient intake in both groups. They excluded dietary supplement use from the calculations.

The researchers also took 60-milliliter blood samples and 24-hour urine samples to observe vitamin and mineral levels. They identified some of these, such as vitamin B12, through biomarkers. For example, high concentrations of holotranscobalamin indicate a vitamin B12 deficiency.

Key research findings

During the 3-day recording, those on a vegan diet showed lower concentrations of cholesterol than the omnivores.

The vegan group also consumed more fiber, vitamin E, vitamin K, and folate. However, these participants did not eat as many foods high in vitamin B12, vitamin D, and iodine as the omnivores.

In the blood, the vegan participants had lower levels of vitamin B2, vitamin B3, vitamin E, vitamin A, selenoprotein P, and zinc than the omnivores. However, they had high levels of folate and vitamin K1.

In the urine samples, iodine and calcium levels were low in those following a vegan diet.

A surprising finding was the lack of vitamin B12 deficiency in vegans. The researchers attribute this to a growing knowledge of the lack of vitamin B12 in plant-based diets.

“Most vegans are aware that a vegan diet is associated with the risk of vitamin B12 deficiency, and vitamin B12 is by far their most frequently taken supplement,” write the authors.

Another interesting finding was that both groups had low iodine levels, although this was more apparent in vegans. Only 8% of vegans achieved adequate iodine levels compared with 25% of omnivores.

Study limitations to consider

Understanding the study’s recruitment process is important when interpreting the data. The authors note that participants were most likely a convenience sample. This means that they chose people who were easy to reach, as they enrolled people who responded to their announcement.

A convenience sample may have created bias in the results, as the people who took the time to respond may already have been health conscious. However, the subjectiveness in recruitment remains debatable.

“Since the same recruitment strategy was used for vegans and omnivores, and a BMI ≥ 30 kg/m2 was chosen as an exclusion criterion, it can be assumed that the level of health consciousness was similar in both groups,” note the authors.

The study also used a small sample size of 72 participants, which is unlikely to be representative of the general population in Germany.

Final thoughts

“Consequently, the results of our study provide first insights into the current vitamin and mineral status in vegans versus omnivores in the German population,” write the authors.

This updated nutritional information could help guide vegans toward prioritizing iodine in addition to vitamin B12 supplementation.

Doing so may help circumvent the health risks associated with following a plant-based diet.

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