10 vitamins and minerals you should never take — and why

2. Synthetic Beta-Carotene

Don’t confuse beta-carotene with vitamin A. While veggies like carrots contain beta-carotene, the synthetic stuff is often made from coal or petroleum, and studies have shown it actually raised lung cancer risk in smokers! Naturally occurring beta-carotene can be protective, but the synthetic version may flip the cancer switch, especially in people with lung damage.

If you see beta-carotene on a label and it isn’t from a natural source, give it a hard pass.

3. Folic Acid (Synthetic Vitamin B9)

Folic acid is the cheap, synthetic version of vitamin B9 you’ll find added to many supplements and processed foods. About a third of people on the planet (maybe you!) have a gene variation (MTHFR) that prevents them from converting folic acid into its usable form, folate. The result? Folic acid builds up in the blood, increasing cancer risk and tanking your immunity.

TIP: Always look for folate (not folic acid) and load up on dark, leafy greens for natural vitamin B9.

4. Synthetic B12 (Cyanocobalamin)

The most common B12 supplement is cyanocobalamin—yes, that “cyano” means it contains a little cyanide. While it’s not instantly deadly, it’s not as effective as natural methylcobalamin and can deplete your body’s glutathione, an essential antioxidant. If you smoke or have certain genetic issues with detox pathways, this combo can be extra risky.

For naturally occurring B12, stick to red meat or liver. Only supplement with methylcobalamin if you need a boost.