Many people may take supplements that contain B vitamins. Some research has linked B vitamins with an increased risk of lung cancer.

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Over recent years, some research studies have found associations between B vitamins and lung cancer.

In particular, some research has linked vitamin B6 (pyridoxine), vitamin B9 (folic acid), and vitamin B12 (cobalamin) to an increased risk of lung cancer.

These vitamins are found in many foods, but they can also be found in multivitamins, B-complex vitamins, or as individual supplements. In some cases, B12 injections may also be prescribed to people with severe deficiencies.

You’ll notice that the language used to share stats and other data points is largely binary, fluctuating between the use of “men” and “women.”

Although we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.

The studies and surveys referenced in this article did not report data on, or include, participants who were transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

Supplementing with B vitamins — especially vitamin B6, folic acid, and vitamin B12 — has been linked with an increased risk of lung cancer.

In a 2019 case-control study involving 5,183 lung cancer cases and 5,183 controls, those with higher B12 blood levels had a 15% higher risk of having lung cancer.

In the same study, researchers compared genetic profiles of 29,266 lung cancer cases and 56,450 controls that were of European descent. Analyses of genes suggested that those with higher B12 concentrations were at an 8% increased risk of lung cancer.

In another 2017 cohort study of 77,118 men and women, men who took vitamins B6 and B12 from individual supplements had a 30–40% increased risk of lung cancer. However, no associations were found in women.

Further, men who were smokers and supplemented with greater than 20 mg of vitamin B6 or 55 mcg of B12 were 2.9 times and 3.7 times more likely to develop lung cancer, respectively.

The researchers compared people who supplemented with B6 or B12 in high doses for 10 years versus those who did not supplement. They found that B-vitamin supplementation increased lung cancer risk in men by almost two-fold.

Regarding folic acid (B9), one study of 1,064 lung cancer cases found no associations between folic acid supplementation and lung cancer risk.

Another study found no associations between serum folate and B6 levels and increased risk of lung cancer.

Interestingly, another cohort study of 159,232 postmenopausal women found that supplementing with ≥50 mg of vitamin B6 resulted in a 16% decreased risk of lung cancer. In addition, B12 and folate (B9) levels were not associated with lung cancer risk.

At this time, it appears there may be a link between megadoses of vitamins B6 and B12 and an increased risk of lung cancer, particularly in men.

That being said, all studies were observational, meaning they cannot prove cause and effect.

While some research does suggest high doses of vitamins B6 and B12 may increase one’s risk of lung cancer, it’s important to keep a few things in mind.

Most people likely do not consume anywhere near the amounts used in research.

According to the National Institutes of Health, men and women consume adequate amounts of these vitamins, usually consuming around the recommended daily amounts.

The recommended daily allowance (RDA) for vitamins B6 and B12 is 1.3 mg and 2.4 mcg, respectively.

Comparatively, the amounts found in one study to be associated with lung cancer were greater than 20 mg of vitamin B6 and 50 mcg of B12. This is 15–20 times the recommended intake and is likely only possible through supplementation.

The study found associations when B vitamins were taken independently rather than as part of a multivitamin. Therefore, it’s important that you always take the amount a healthcare professional recommends.

Further, many studies on B vitamins and lung cancer are observational, meaning they can only look at associations. This means they cannot prove that B vitamins cause cancer but rather that there may be a link.

At this point, there are conflicting data on whether B vitamins — especially vitamins B6, B12, and folic acid — are associated with lung cancer.

If there is, it appears to be only at very high doses, which most people should avoid consuming.

In some cases, supplementing with B vitamins may be important.

Certain populations, such as vegans, vegetarians, older adults, and those with pernicious anemia, may need to supplement with B12.

Further, people with alcohol use disorder, renal insufficiency, or autoimmune conditions may need to supplement with B6.

Finally, it’s important that pregnant people or those planning to become pregnant ensure that they’re getting enough folate in their diet to prevent neural tube defects. In some cases, their healthcare professional may recommend folic acid (the supplemental form of folate).

If you think you need a supplement, consult with a healthcare professional and if needed, only take the recommended amounts.

Many commonly consumed foods are good sources of B vitamins. Here are some examples of foods high in B6, folate (B9), and B12.

Vitamin B6 food sources

  • pork
  • beef and beef liver
  • chicken and turkey
  • certain types of fish, including tuna and salmon
  • soybeans
  • chickpeas
  • bananas
  • cow’s milk
  • fortified breakfast cereals

Vitamin B9 (folate) food sources

  • white rice
  • sorghum
  • beef liver
  • leafy greens, including mustard greens and romaine lettuce
  • non-starchy vegetables, including asparagus, green peas, and Brussels sprouts
  • some fruits, including avocado, cantaloupe, banana, and papaya
  • fortified breakfast cereals
  • baker’s yeast
  • eggs
  • whole grain or enriched white bread

Vitamin B12 food sources

  • beef and beef liver
  • chicken and turkey
  • tuna, salmon, and other fish
  • clams
  • cow’s milk
  • fortified plant beverages
  • fortified breakfast cereals
  • tempeh
  • nutritional yeast
  • eggs
  • cow’s cheese

Supplementing with B vitamins has been linked with an increased risk of lung cancer.

In particular, according to one study previously cited, it appears that megadoses of vitamin B6 and vitamin B12 — around 20 mg or 50 mcg, respectively — are linked with a higher risk of lung cancer. That said, not all studies have confirmed this.

In most cases, people can only consume such high doses from supplements rather than food, so it’s important to pay attention to the ingredient label if you do require a supplement.

When in doubt, it’s best to listen to the advice of a healthcare professional and only supplement as needed. Instead, focus on a food-first approach when trying to get in your daily nutrients.