Studies have shown that a vitamin B12 deficiency in pregnant women can damage the baby's brain development. However, many people with autism have too much B12, according to a new Norwegian study.

Many people on the autism spectrum have too much vitamin B12, which is important for brain development and thinking

Sigrun Hope is a consultant and specialist in psychiatry. She thinks she has uncovered what she calls “a small mystery”.

As a physician, Sigrun Hope has long suspected that some of her patients who are on the autism spectrum have an excessive level of the vitamin B12.

Other research has shown that women with too little B12 during pregnancy can damage a child's brain development.

Medical theory has held that B12 levels cannot become excessive because the body regulates itself by excreting any excess of the vitamin through pee or stools.

Significantly more cases with high B12 levels

“I’ve been a psychiatrist for 25 years and have wondered for years why my patients with autism have such high B12 levels, even though they haven’t taken vitamin supplements. I thought this was really strange,” says Hope.

A few years ago, an American study showed that pregnant women with high levels of B12 were more likely to have children with autism.

This piqued the psychiatrist’s curiosity even more.

Now she and colleagues at Oslo University Hospital have conducted a study where they examined blood tests for Norwegian patients on the autism spectrum. The study confirmed her experiences from the clinic.

The study shows that significantly more people with this diagnosis have a high level of vitamin B12 compared to healthy ones.

Didn't apply to patients with schizophrenia

The researchers also measured the level of the vitamin in patients with schizophrenia. This group’s B12 level was within the normal range.

The study is part of the so-called BUPGEN project at Oslo University Hospital. This project involves researchers trying to find new information about what causes someone to develop autism spectrum disorder.

Importance for brain development

Vitamin B12 is of great importance for brain development and cognitive function, in other words, the ability to think.

I’m seeing that something doesn’t agree with the theory here. I think we need to figure this out before we give people advice about taking B12 supplements," says Sigrun Hope.

A Norwegian study from 2018 brought this to light in an article published in the scientific journal Nature.

The researchers examined genetic factors that influence our ability to remember new words. They found that what was most closely related to word memory was a protein called TCN1. This is the same substance that transports B12 through the blood.

Little research available on excessive B12

B12 is a vitamin that has been extensively researched for many years.

Much of the focus has been on how harmful it is to the body to have too little of the vitamin.

However, little research has been done that looks into how excessive B12 could be harmful,” Hope says.

Research has shown that a lack of B12 can cause memory impairment and dementia in the elderly. Prolonged B12 deficiency can cause damage to the nervous system.

It has also been shown that a lack of B12 in pregnant women can damage the baby's brain development.

Many study participants receive supplements

A study from the University of Bergen has shown that two-thirds of pregnant women had lower than recommended B12 levels.

Researchers in Bergen are now conducting several large clinical studies looking at the effect of giving B12 to pregnant women and young children.

The studies are being conducted in Norway, Nepal, India and Tanzania.

The most important brain development occurs in pregnancy and the first years of life. Researchers want to see if the B12 level is related to brain development in children.

Is autism caused by B12 supplements?

Hope and her colleagues were interested in whether individuals with autism whose B12 level was too high had received supplements during pregnancy.

The researchers created a subgroup of the participants to study this question, but they did not find any such link.

Another new Norwegian study published in The Journal of Nutrition, in which researchers measured the level of B12 in toddlers, likewise did not find any connection between supplementation and vitamin level in the children’s blood.

Is lifestyle a cause?

People on the autism spectrum often live somewhat differently than healthy people.

They tend to have poorer finances. They more often have a disability. They often live alone and have a different diet and lifestyle than the rest of the population.

Diet could have been an explanation to the high levels of B12, Hope believes.

“People with autism can in many ways be compared to people with schizophrenia, in terms of socio-economic factors and lifestyle. It has been interesting to study this group to control for all the factors that might otherwise be difficult to control.

But the scientists didn’t find any link here, either.

People with schizophrenia had the same B12 level as the healthy control group.

Important reminder

Tor Strand is a professor at the University of Bergen’s Centre for International Health and Innlandet Hospital. He heads the projects for B12 supplementation in Norway, Nepal, India and Tanzania.

Strand has read Hope's study and finds it interesting, but points out that it is important to have this confirmed in clinical trials.

Tor Strand believes that it isn’t possible to use this finding to claim that high doses of B12 are dangerous.

“Studies like this serve as an important reminder for those of us who work with vitamins, minerals and nutrition that there is a limit to all nutrients. For iodine and iron, it doesn't take much to reach doses that are too high. For vitamin B12, on the other hand, the vast majority of people can tolerate high doses,” Strand says.

Warns against strong conclusions

However, he cautions against drawing strong conclusions yet.

When you start with a clinical population like this, the findings are often a bit scary. You can find strange things that are difficult to explain, he says.

“It’s also difficult to interpret data from a cross-sectional study because you get the classic hen and egg problem. What comes first? Is it the disease that causes higher levels of the vitamin or is it a high vitamin level that causes the condition?” he asks.

Strand believes it is important to remember that the blood’s B12 levels can change throughout the day, whereas developmental disorders like autism develop over years, in pregnancy and early childhood.

Do people with autism eat differently?

Strand believes that when researchers study three different subgroups of a population, as was done in this study, there is good reason to believe that the groups may have different nutritional profiles.

“The researchers haven’t looked at what people eat, just whether a subgroup takes vitamin supplements or not. Perhaps people with autism have different eating habits than others?

Certain foods contain a lot of vitamin B12, like fish, meat and cow's milk.

Anorexia and cancer

Vitamin B12 is the largest and perhaps the most structurally complex vitamin we have in our body, Strand says. It is absorbed in the interactions between the mouth, stomach and small intestine.

“If something in the body isn’t working properly, the concentration of B12 in the blood can be affected,” he says.

Numerous diseases are associated with high B12 values, such as lung cancer.

Other studies have shown that B12 can have a growth-promoting effect on established or early-stage cancers.

Some studies indicate that high levels of B12 are related to poor nutrition and bowel problems.

An association between anorexia and high levels of B12 has also been shown.

"It’s been suggested that a high level of the vitamin may represent a form of acute phase reaction, similar to other levels – such as ferritin and CRP – that increase when talking about an underlying disease process," Hope says.

Still a mystery

What are the commonalities between various diseases like cancer, anorexia and autism?

So far, it remains a mystery for researchers.

“We simply don't know,” says Hope.

“I’m seeing that something here doesn’t agree with the theory. I think we should figure it out before we give people advice on taking B12 supplements,” she says.

Supplements usually not dangerous

However, Strand believes that this finding cannot be used to claim that normal or high doses of B12 supplements are dangerous.

“This is a vitamin that the body usually regulates well by itself. Regular vitamin supplements that give you a recommended daily dose don’t lead to a dangerous build-up in the body. Vitamin B12 is actually something we can store effectively. Our body can access these stores during periods of low intake. But, if high doses are being prescribed, the patient's B12 level should still be examined first,” he says.

Translated by Ingrid P. Nuse


Sigrun Hope et al: Higher vitamin B12 levels in neurodevelopmental disorders than in healthy controls and schizophrenia, The Faseb Journal, April 2020.

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