Scientists have been studying the link between Vitamin B12 levels and cancer risk, with a 2025 study finding both too high and too low levels may be associated with increased risk
In a new article experts cautioned against ‘megadosing’ on supplements
B12 is a vitamin that is absolutely vital for the body. It assists in producing red blood cells, maintains the nervous system’s function, and plays a fundamental role in how cells replicate and repair DNA.
It must be obtained from food as the body cannot manufacture it. When the body lacks sufficient amounts – which can occur for various reasons – it can trigger a broad spectrum of symptoms and potentially lead to irreversible damage.
However, a new report has revealed a connection between cancer and B12 – highlighting that the primary concern arises whether you have excessive levels or insufficient amounts.
B12 occurs naturally in animal products including meat, fish, eggs, milk and cheese. Certain cereals and breads are also fortified with it, enabling those who don’t consume meat to obtain adequate amounts.
People have been warned about overdosing on B12 supplements(Image: Getty)
Most people eating a balanced diet receive the recommended quantity, but vegans, individuals with particular digestive conditions and elderly adults who absorb nutrients less effectively may require supplements.
Writing on The Conversation website, Ahmed Elbediwy, Senior Lecturer in Cancer Biology and Clinical Biochemistry, Kingston University, and Nadine Wehida, Senior Lecturer in Genetics and Molecular Biology, Kingston University explained the consequences of inadequate levels. They said: “, reports the Mirror.
Without enough B12, things can go wrong, sometimes seriously, especially if deficiency is not recognised and treated.” On the subject of cancer, they highlighted that the new research had thrown up some concerning findings: “In recent years, researchers have been asking whether high levels of B12 intake or high levels of B12 in the blood could be linked to cancer.
“The body is constantly making new cells. Every time a cell divides, it needs to copy its DNA accurately. Vitamin B12 is critical to that process. When levels are too low, DNA can be copied incorrectly, leading to mutations that, over many years, may increase the risk of certain cancers, particularly colon cancer. This is why B12 deficiency is taken seriously.
“A 2025 case-control study from Vietnam found what researchers described as a U-shaped relationship between B12 intake and cancer risk, with both lower and higher intakes associated with increased risk. Because this kind of study can show an association but cannot prove cause and effect, the takeaway is not that B12 is dangerous. It is that balance matters.”
Also known as cobalamin, B12 is essential for life. It helps the body produce red blood cells, keeps the nervous system functioning, and plays a central role in how cells copy and repair DNA.
Regarding B12 as a potential safeguard against cancer, the scientists stated: “It might seem logical that if B12 helps healthy cells thrive, taking extra doses should offer extra protection against cancer. But research does not fully support this. Vitamin B12 supports cell growth generally, not only the growth of healthy cells. One concern is that, if pre-cancerous cells are already present, very high availability of growth-supporting nutrients such as B12 could, in theory, support their growth too. But this remains difficult to prove in humans.
“Overall, studies of high-dose B vitamin supplements taken over long periods have not shown clear protective effects against cancer incidence or cancer deaths.”
The scientists noted that certain ‘observational research’ suggested a slight increase in lung cancer risk linked to long-term, high-dose B6 and B12 supplementation, particularly amongst men and smokers, ‘although this kind of study cannot prove that the supplements caused the cancers’.
The connection between cancer and B12 was partly brought to light after doctors observed elevated levels in the blood of patients, however research in 2022 revealed that B12 appeared alongside the disease – but was not responsible for triggering it.
Symptoms of vitamin B12 and folate deficiency anaemia include:
rapid breathing or shortness of breathheadachesindigestionloss of appetitepalpitationsproblems with your visionfeeling weak or tireddiarrhoeaa sore or red tongue, sometimes with mouth ulcersproblems with memory, understanding and judgment (cognitive changes)
Vitamin B12 deficiency can also cause symptoms that affect your brain and nervous system (neurological symptoms), including: Testing can help detect how the cancer is progressing, they explained: “Researchers are also recognising that elevated B12 may not be a cause of cancer, but it could be a useful marker of whether cancer is present or progressing. A large 2026 study found that colon cancer patients with very high B12 levels survived a median of around five years, compared with nearly eleven years for those with normal levels.
“Similar patterns have been found in oral cancer and in patients receiving immunotherapy, where elevated B12 has been associated with poorer outcomes. This means that unexplained, persistent high B12, especially when it is not caused by supplements, should not be ignored. It may point to liver disease, blood disorders or an underlying cancer that has not yet been detected.
Also known as cobalamin, B12 is essential for life. It helps the body produce red blood cells, keeps the nervous system functioning, and plays a central role in how cells copy and repair DNA.
“For most people, this is not something to worry about. B12 from a normal diet containing meat, fish, eggs, dairy or fortified foods is not usually the issue: it is very difficult to consume too much B12 from food alone. Deficiency remains a more common and better-established problem than excess. The concern is prolonged high-dose supplementation without medical advice, or a blood test showing persistently high B12 when someone is not taking supplements.”
The researchers emphasised that the key message is ‘more is not better’ – and maintain a balanced diet alongside a healthy lifestyle. Regarding B12, they added: “Get enough through food or supplementation if you need it, especially if you are vegan, older or have a condition that affects absorption. But leave the megadoses on the shelf unless a doctor advises them. With B12, as with many nutrients, the goal is not as much as possible. It is the right amount.”
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