Niacin, also known as vitamin B3, is a common vitamin used to lower cholesterol and improve heart health. It’s also used to manage high levels of fats in the blood.
While niacin can be helpful when taken correctly, using too much can cause serious side effects—including damage to your eyes.
A new report from the New York Eye and Ear Infirmary of Mount Sinai shows how dangerous high doses of niacin can be if not taken under a doctor’s care. In one case, it even led to temporary blindness.
The case involved a 61-year-old man who lost much of his vision over one month. When he arrived at the hospital, his eyesight had become so bad that he was close to being legally blind. He could only see large letters on an eye chart—20/150 in one eye and 20/100 in the other.
At first, the man only told doctors about his high blood pressure and high cholesterol. He didn’t mention that he had been taking large amounts of niacin.
Later, he explained that he had been taking between 3 and 6 grams of niacin each day for several months, hoping to prevent heart problems. He bought the vitamin over the counter and didn’t know that taking this much could be harmful.
Doctors said that the normal amount of niacin for cholesterol is between 1 and 3 grams per day. Although 6 grams is the maximum dose, it should only be taken with a doctor’s supervision. Taking too much niacin without medical advice can be dangerous, even though it’s easy to buy in stores.
Using special eye imaging tools, the doctors found that the man had developed a rare condition called niacin-induced cystoid maculopathy. This condition causes swelling in the macula, the part of the eye that helps you see details clearly. Too much niacin caused fluid to build up in his retina, leading to blurry vision.
Thankfully, the doctors acted quickly. They told the man to stop taking niacin right away. Within a week, his vision began to improve. Two months later, the swelling was gone, and his eyesight had returned to normal—20/20 in both eyes.
This case is a warning about the risks of taking high doses of vitamins without guidance from a healthcare provider. Just because a supplement is easy to buy doesn’t mean it’s completely safe. High doses can cause unexpected and serious health problems.
If you are thinking about taking large doses of any supplement, especially niacin, talk to your doctor first. And if you notice any sudden changes in your vision, seek medical help immediately. Your eyes—and your overall health—depend on it.
This study, led by Dr. Richard Rosen, was published in the Journal of VitreoRetinal Diseases. It reminds us how important it is to use supplements responsibly and always get advice from a medical professional.
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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