Daily, millions of individuals consume vitamin tablets with the expectation that they will improve their health and fortify them against life-threatening conditions like cancer.
Consumers in the United Kingdom spent over £500 million on dietary supplements in 2022, with iron and calcium supplements and vitamins C, D, and B12 being the most popular.
Approximately one-third of the population consumes dietary supplements in the belief that they will enhance health and prevent disease.
However, some vitamin supplements may have the opposite effect.
A recent study, published in August in the Journal of Clinical Investigation, found that mice with lung tumours grew and spread more swiftly when regularly supplemented with high doses of vitamins C and E.
The Unexpected Effects of Vitamins C and E
Vitamin C is essential for wound healing and maintaining healthy skin, blood vessels, bones, and cartilage in humans; vitamin E is critical for immunity and eye health.
Despite their abundant presence in commonplace foods, approximately one-fourth of the population consumes vitamin C supplements on a daily basis, either standalone or in conjunction with a multivitamin regimen.
Additionally, it seems that a considerable number of individuals hold the belief that supplementing with vitamin C in large quantities can effectively protect against winter colds and influenza.
The Impact on Tumour Development
Nevertheless, alarming new research from the Karolinska Institute in Stockholm, Sweden, indicates that exceeding the body’s requirements for these two vitamins promotes the development of lung cancer by facilitating the formation of new blood vessels that supply the disease with more oxygen-rich blood, thereby aiding in its metastasis.
In the investigation, scientists introduced lung cancer cells into rodents via injection prior to supplementing them with escalating quantities of vitamins C and E via their drinking water.
They performed routine ultrasound examinations to track the development of blood vessels, which are essential for the solidification of the cancer cells into a tumor.
Although there is no evidence to suggest that an overabundance of vitamins C and E causes lung cancer, the researchers hypothesised that it might accelerate the development of cancer in patients who have not yet been diagnosed with the disease.
And even though researchers conducted the study on rodents, the results raised concerns that high-dose vitamin supplement consumption may pose comparable dangers for humans.
Vitamins C and E are antioxidants, which means they ordinarily protect cells from damage caused by harmful free radicals (molecules generated by metabolic processes such as breathing and environmental factors such as pollution). Consequently, these results were unexpected.
Professor Martin Bergo, a nutrition and biosciences expert who directed the study at the Karolinska Institute, elaborated: “These antioxidants stimulate a process by which cancerous tumours generate new blood vessels.”
This finding is unexpected, as it was previously believed that antioxidants provided protection.
The researchers emphasised that there is insufficient evidence to suggest that ingesting vitamins and minerals present in reduced concentrations in common foods is detrimental.
Exploring the Impact of Supplements on Cancer Risk
Nonetheless, this is not the first study to suggest a link between excessive supplement consumption and tumour development. A 2019 study published in the journal Annals of Internal Medicine found that taking high-dose calcium supplements (greater than 1,000 mg per day) doubled the risk of dying from any form of cancer among 27,000 U.S. adults followed for 12 years.
Adults require approximately 700 mg of calcium per day to maintain healthy bones and teeth, a normal circulation, and blood clotting. “You should be able to get all the calcium you need from your daily diet,” according to the NHS. This consists of oranges, cheese, milk, almonds, spinach, and legumes, among other foods.
The NHS specifically advises patients diagnosed with osteoporosis, a bone-thinning disease, regarding the necessity of increasing their calcium consumption for the purpose of safeguarding their bones.
Pharmacies offer over-the-counter calcium supplements in various dosage forms, including 800 mg. Healthcare professionals generally recommend that consumers take one to two supplements daily.
The NHS states that daily calcium intake in excess of 1,500 mg can cause stomach distress and diarrhoea. However, a study conducted in the United States by researchers at Tufts University in Massachusetts concluded that for some individuals, the long-term adverse effects of calcium supplementation could be significantly more severe.
Importantly, the study also discovered that increasing the consumption of calcium-rich foods did not significantly increase the risk of cancer-related mortality. Excessive supplement intake limited the hazards. Controversial were these results, given that prior research had demonstrated that calcium supplementation reduced the risk of developing tumours, particularly colon cancer.
Examining Beta-Carotene Supplements and Lung Cancer Risk
And the Tufts researchers emphasised that there is neither conclusive evidence nor a clear mechanism by which calcium tablets could cause cancer.
In contrast, researchers have linked beta-carotene, an additional well-known supplement, to an increased risk of lung cancer in individuals who smoke in the past.
The pigment beta-carotene is responsible for the distinctive yellow and orange hues of fruits and vegetables; excellent sources include mangoes, apricots, carrots, and red peppers.
Vitamin A, produced by the body from beta-carotene, is essential for good eyesight, a robust immune system, and fertility.
Numerous studies, including the most recent one published in August in the journal Nutrition Reviews, have established a correlation between beta-carotene supplements and lung cancer.
The present investigation, conducted by scholars at Tsinghua University in Beijing, synthesised data from eighteen prior studies pertaining to the subject matter. They determined that beta-carotene supplements increase the risk of lung cancer in smokers by approximately 16%, even at modest doses.
Unless otherwise prescribed by a physician, the Department of Health and Social Care advises against taking more than 7 mg of beta-carotene per day (some supplements contain 15 mg per tablet), and smokers should avoid them entirely due to the risk of lung cancer.
In contrast, the World Cancer Research Fund asserts that certain high-dose supplements may have detrimental effects. Including beta-carotene supplements at high doses, which have been found to elevate the risk of lung cancer in both smokers and non-smokers.