Millions of Americans visit their local CVS and other stores to get stocked up on vitamins and supplements. These products are part of a daily health regimen for many men and women (as well as non-binary folks) and can help you lead a healthier and longer life. However, experts warn that there are some vitamins and supplements that need to be monitored very closely because taking too many of them can lead to potentially harmful side effects that might lead to going blind or developing liver damage.

One vitamin that you need to not take too much is niacin, which is part of the B group of vitamins and is sometimes called vitamin B3. Niacin is a critical vitamin that helps our nervous system function and helps support our metabolism by aiding the process of turning the food we eat into the energy our bodies need to function.

Additionally, cells in the human body require niacin to function and develop. There is also evidence to suggest that getting niacin in your diet can help be a powerful nutrient to support heart health. Sometimes doctors can prescribe niacin along with statins for people struggling with high cholesterol. This has led the vitamin industry to tout niacin as having heart health benefits, causing many people to treat themselves with the vitamin, which may cause more harm than good if not done under the supervision of a doctor.

However, ingesting too much niacin can be toxic to the human body. The healthy amount of niacin for women is about fourteen milligrams (mg) per day, but popular supplements provide as much as 500 mg per day of this potentially toxic vitamin.

One scientific study from a team of doctors in New York claims that they were treating a 61-year-old man who suddenly experienced blindness. A test confirmed that the man could be classified as legally blind. Eventually, doctors learned he was self-treating his high cholesterol with excessive doses of niacin. Doctors found that the patient was consuming between three and six grams of niacin daily for several months and concluded that this was what caused his sudden blindness.

Doctors diagnosed the man with niacin-induced maculopathy after confirming that niacin caused damage to his retina. Fortunately, the man discontinued the use of niacin, and his vision cleared up in due time.

This patient was taking far and above the recommended daily dose of niacin. But taking as much as 1,000 mg per day can come with other health complications, including dizziness, splitting headaches, low blood pressure, high blood sugar, heartburn, stomach pain, and nausea. For those taking even higher doses of niacin, the symptoms can be worse and include muscle damage, stomach ulcers, and possible liver damage.