Vitamin B3, also known as niacin, is a common vitamin used to lower cholesterol levels and treat a condition called hyperlipidemia.
It comes in both prescription and non-prescription forms and is widely used by people who want to improve their heart health. But while niacin can be helpful, taking too much of it can cause serious health problems—especially for your eyes.
A study from the New York Eye and Ear Infirmary of Mount Sinai warns people about the dangers of taking high doses of niacin without medical advice. In one case, a man who took large amounts of niacin experienced temporary blindness. This surprising side effect shows how important it is to use vitamins safely.
The study focused on a 61-year-old man who came to the hospital because he was losing his eyesight. Over the span of a month, his vision became so bad that he was close to being legally blind.
When tested, his vision was found to be 20/150 in one eye and 20/100 in the other. At first, he only told doctors about his high blood pressure and cholesterol. He did not mention that he had also been taking large amounts of niacin.
Later, he admitted that he had been taking between three and six grams of niacin every day for several months. He bought the supplements over the counter and believed that the vitamin would help lower his risk of heart disease. What he didn’t realize was that this much niacin could be dangerous.
Doctors explained that when niacin is used to treat high cholesterol, the normal dose is usually one to three grams per day. Even the maximum recommended dose is six grams—and that’s only under medical supervision. This man was self-medicating without a doctor’s guidance, which put him at serious risk.
The medical team used special eye imaging tools to figure out what was wrong. They diagnosed him with a rare condition called niacin-induced cystoid maculopathy. This condition causes the center part of the retina, called the macula, to swell. The macula helps us see fine details, so any damage to it can make vision blurry or distorted.
In this case, the swelling was caused by fluid building up in the macula due to the high levels of niacin in his body. The good news was that the condition could be reversed. Doctors immediately told the man to stop taking the niacin.
After just one week, his vision started to get better. Within two months, the swelling was gone and his eyesight had returned to normal—20/20 in both eyes.
This case is a clear reminder that even common vitamins can be harmful if not used correctly. Just because you can buy something without a prescription doesn’t mean it’s safe in large amounts. People who depend on good vision for work or everyday life should be especially careful.
The researchers stressed that it’s always best to talk to a doctor before using supplements to treat any health condition. Prescription drugs are carefully controlled and monitored by professionals to make sure they are safe. Over-the-counter vitamins, on the other hand, don’t come with the same protections.
This research, led by Dr. Richard Rosen and published in the Journal of VitreoRetinal Diseases, shows why we need to take vitamins seriously. With the right guidance, supplements can be helpful—but without it, they can sometimes do more harm than good.
If you care about eye health, please read studies about how vitamin B may help fight vision loss, and MIND diet may reduce risk of vision loss disease.
For more information about eye disease, please see recent studies about how to protect your eyes from glaucoma, and results showing this eye surgery may reduce dementia risk.
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