Can Vitamins and Other Dietary Supplements Cause Cancer? Probably.

William Keckler
5 min readJan 20, 2019


A number of studies in recent years have sounded the alarm that daily consumption of manufactured vitamins and other dietary supplements, in quantities most would not consider excessive at all (often the product’s recommended dose) appear to increase the risk for certain cancers.

Vitamin B12 and vitamin B6 supplementation have been linked to an increased risk for lung cancer. Oddly enough, this alarming cancer spike occurred only in men taking these supplements. There was no significant increase in risk for women taking these same supplements. The risk appears to be greatest in smokers, but non-smokers are also at risk. Those taking supplemental folic acid (vitamin B9) in combination with high doses of vitamin B12 appeared to have the highest risk of developing lung cancer (along with a general increase in non-cancer-related mortality rates) according to a study by the Fred Hutchinson Cancer Research Center in Seattle.

The individuals in the study were typically taking the “recommended doses” of these vitamins. Many bestselling supplement manufacturers have amped up the percentages of recommended daily doses in their formulations, since the prevailing wisdom until recently has been that no harm could result.

For example, until recently I was taking a B12 supplement that packed a walloping 104,000 % (that’s not a typo) of the recommended daily dose of the vitamin. This is typical for products on the shelf at your Walmart or CVS store. The prevailing wisdom for decades has been this: “Since B12 is a water-soluble vitamin, it’s generally considered safe, even at high doses. No Tolerable Upper Intake Level (UL) has been established for B12, due to its low level of toxicity. UL refers to the maximum daily dose of a vitamin unlikely to cause adverse side effects in the general population.”

Many people start taking vitamins and other supplements because they read or hear those Pollyanna stories in the news mentioning various studies where certain vitamins or supplements seem to confer a protective advantage. A study comes out in Japan stating that vitamin D3 may help to prevent liver cancer. Bang! Tens of thousands of people start supplementing with vitamin D3. Then another study comes out stating that high vitamin D levels have been “linked with an increased risk of skin, prostate and blood cancers,” although also with “a decreased risk of lung cancer.”

Killer cure? Clearly, it’s best to get the whole picture, not just the media sound blips on vitamins and other supplements. But it’s not always so easy to do. Nothing is centralized. The health news picks up one story on a vitamin or supplement and runs with it, and buries another. Dr. Oz might tout the sunny news on Supplement X, but not tell you about that recent study in Scandinavia on that same supplement, sounding the tocsin on a potential toxin. This really bites. Because you wanted to do something to improve your health. You wanted to be proactive. And then you read a study which reveals you might just be taking the Miracle-Gro of cancer.

An article at Consumer Lab lards on more grim news. Supplemental vitamin E, beta carotene and selenium have all been found to have associations with various forms of cancer. But it’s complicated. For example, “low dose vitamin E may help prevent prostate cancer, but high-dose vitamin E may increase it.” A study showed a similar situation with vitamin D, where being too low or too high might present a risk situation. Vitamin and other dietary supplementation, it seems, requires a mindset of brinkmanship.

So you just have to learn how to be an alchemist of vitamins! Sure, we all have time for that. And maybe you can pick up a degree in bioinformatics while you’re at it. It might help. Because this is complicated and constantly proliferating data to assay. We can try to fine-tune our health and build it up with supplements, but if we push it too far, build too high, it turns into a house of cards and comes tumbling down. Probably nobody knows where the “fine line” is at this point.

It’s important to point out that a certain vitamin or other supplement being linked with cancer does not necessarily mean that it causes cancer. There may be co-factors or other risk factors which contribute to the epidemiological outcome. While that may be true, statistical caveats aside, these recent studies made me rethink my use of certain supplements. I limited drastically my intake of some and cut others out altogether. It’s amazing how prevailing medical wisdom, soi-disant, can undergo a sea change in a matter of a handful of years, after decades of a unified front of medical consensus. Vitamins were regarded as enhancing health, at best, and merely producing “expensive urine” at worst: a kiddie pool of health enhancement exploration.

As these stories about the risk of supplements broke, as the ill-tidings rolled through the news feeds, the Linus Pauling Institute, true to the spirit of its founder, launched a spirited defense of vitamin supplements. It’s obvious that vitamins are essential to life and health. But, in light of all these recent studies, it seems vaguely hubristic to be the anti-Cassandra standing there shouting, “Vitamins do not cause cancer!” Clearly, the jury is out and deliberating a long time. This may not be an open and shut conviction.

One has to seriously ponder whether the time has come for the FDA to begin requiring warnings on the packaging of these products consumed by countless millions. The Dietary Supplement Health and Education Act (DSHEA) of 1994 does not require manufacturers of vitamins and other dietary supplements to disclose risks the way that pharmaceutical manufacturers must. In light of numerous recent studies pointing to the likelihood that vitamin and supplement consumers are becoming the new cancer lab rats, we should rethink that decision. In the meantime, I think I’m going to try to get most of my vitamins from superfoods and forego many of the OTC versions. The next time I’m offered one of these wonders in a plastic bottle, I’m going to say, “No thanks. I like my vitamins rare.”



William Keckler

Writer, visual artist. Books include Sanskrit of the Body, which won in the U.S. National Poetry Series (Penguin).