An oncologist says an easily available pill millions take every day could increase your cancer risk up to 30 per cent. Dr Mohammad Muneeb Khan of charity Killing Cancer Kindly says multivitamin products should be labelled with warnings due to the dangers.

Oncologist Dr Khan says supplements 'bombard the body with huge doses of wholly unnecessary nutrients' - which may enable cancerous cells to grow and multiply. Natural vitamins found in foods are absorbed slowly, and the body takes only what it needs before flushing out the rest.

The charity says synthetic pills 'flood' the bloodstream with up to twice the recommended daily dosage of nutrients, becoming a 'superfood' for cancers. Multivitamin supplements could also increase the risk of developing other cancers such as prostate cancer, bowel cancer, and breast cancer, the charity added.

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The charity is calling for a change in legislation to force manufacturers of multivitamins to include warning labels on their packaging. The warnings appear in Dr Khan's book ‘You’ll Wish You Were an Elephant (Killing Cancer Kindly)’, a guide to preventing cancer in adults.

Dr Khan said: “Synthetic pills contain obscenely high and wholly unnecessary volumes of micronutrient that far exceed what the average human body requires. These tiny organic compounds are so numerous that our organs struggle to use them, and they’re left, in effect, to float about the body.

“The problem is that these excess multivitamins are readily available to feed the hundreds of potentially cancerous cells that are made in our body every day. Normally, our body has the capability to destroy these cancer cells effectively but this becomes a challenge when they are well fed and able to increase in number quickly.

“Imagine hundreds of ravenous little Pac-Men running around and gobbling everything up and then multiplying in number exponentially over time until they are able to completely overrun our body’s anti-cancer defences such as the immune system. The solution, as controversial as it may at first appear, is to reclassify multivitamins as a drug and make people aware of their side effects.

“A health warning and prescription would work best alongside the general advice that most people, children and adults alike, do not need additional vitamins in their diet, period.”

Almost half of Brits are thought to take a daily supplement, which usually contain a broad spectrum of compounds said to help maintain normal metabolic function. KCK says that there is a growing body of “compelling” research that suggests a direct link between synthetic vitamin consumption and increased rates of lung cancer, prostate cancer, bowel cancer, and breast cancer.

The risk is said to be the same for all adults regardless of whether they live an otherwise healthy lifestyle. The charity says cancer cells have up to 10 times the capacity of normal healthy cells to absorb nutrients floating around the body – including vitamins.

Natural vitamins, obtained from foods such as fruits and vegetables, are said not to pose the same dangers because of the relatively small quantities released into the body during the digestion process. Unlike their synthetic counterparts, they are “locked away” in the food with only a fraction being broken down and absorbed before undigested food is excreted – typically within 24 hours.

But being concentrated, supplements are rapidly and readily absorbed, leaving an excess of vitamins circulating the blood stream and just waiting to be “mopped up” by cancer cells before they can be processed or excreted.

Describing the situation as a “ticking health timebomb”, Dr Khan is calling for action to curb their use. He wants to see manufacturers being made to include a mandatory health warning on the front and back of packaging like those found on tobacco products.

Dr Khan, who is also the author of The How, What & Why Of Cancer: Separating Fact from Fiction, added: “There is a growing body of scientific research pointing to synthetic multivitamin supplements increasing the risk if used daily over a prolonged period.

“In one flagship study, the CARET trial, the increased risk of developing lung cancer from taking a daily supplement including vitamin B6, B9 and B12 was estimated to be nearly 30 per cent. Studies looking at the daily use of supplements including vitamin A and vitamin B complex (including vitamins such as B1, B6 and B12) have, likewise, shown a correlation in increased risk for different types of cancer, though more research is required to confirm by how much.

“And while research is likewise lacking at present for other vitamins, it’s fair to assume they will also have similar effects. Natural vitamins pose no danger as they are released slowly in the body so we only take what we need but synthetic multivitamins are rapidly absorbed, flooding the body with far more than it can use.

“This is great news for cancer cells as they can take in 10 times the quantity of vitamins and other nutrients that normal healthy cells can, speeding up their growth and reproduction and overwhelming our body’s abilities to destroy them.”