Niacin, also known as vitamin B3, is often used to lower cholesterol levels. It can be bought with a prescription or over the counter as a supplement.
While niacin can be helpful for some people, taking too much of it can lead to serious health problems—including vision loss.
A new study from the New York Eye and Ear Infirmary of Mount Sinai shows how high doses of niacin can harm the eyes. The researchers reported a case where a man temporarily lost much of his vision after taking too much of this vitamin.
The case involved a 61-year-old man who came to the hospital because his vision had become very blurry in both eyes. Within one month, his vision had worsened to the point that he was nearly legally blind. Tests showed he could only see 20/150 in one eye and 20/100 in the other with glasses.
At first, the man told doctors he had high blood pressure and high cholesterol, but he didn’t mention taking any supplements. Later, he revealed that he had been taking between three and six grams of niacin every day for several months. He believed the vitamin would help protect him from heart disease and had bought it over the counter without speaking to a doctor.
Doctors explained that the usual dose of niacin for managing cholesterol is between one and three grams per day. A six-gram dose is the maximum amount and should only be used under medical supervision. Taking large doses without a doctor’s guidance is risky.
Using special imaging tests, the doctors diagnosed him with a rare condition called niacin-induced cystoid maculopathy. This condition causes swelling in the macula, which is the central part of the retina that helps us see fine details. The high dose of niacin had caused fluid to build up in this area, making the man’s vision blurry.
The good news is that the condition was reversible. The doctors told him to stop taking niacin right away. After just one week, his vision began to get better. Within two months, the swelling went away completely, and his vision returned to normal—20/20 in both eyes.
This case is a strong reminder that just because vitamins are easy to buy doesn’t mean they’re always safe. Taking too much can have serious side effects, especially for something as important as your eyesight.
People who depend on good vision for work or everyday tasks should be very careful with supplements. It’s always best to talk to a doctor before starting any new treatment, even if it’s something you can buy without a prescription.
The study was led by Dr. Richard Rosen and published in the Journal of VitreoRetinal Diseases. It shows the importance of using supplements wisely and with proper medical advice to avoid serious health risks.
If you care about nutrition, please read studies about the harm of vitamin D deficiency you need to know, and does eating potatoes increase your blood pressure?
For more information about health, please see recent studies about unhealthy habits that may increase high blood pressure risk, and results showing MIND diet may reduce risk of vision loss disease.
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