April 16, 1999
(NYT Syndicate) - Patients taking large amounts of vitamin A to combat degenerative eye disease need not worry about liver damage, a new study shows.
Massachusetts researchers followed 146 patients with retinitis pigmentosa who took high doses of the dietary supplement for five to 12 years. The patients developed no signs of liver problems, according to their report in the American Journal of Clinical Nutrition.
Still, no one should take high doses of vitamin A without a doctor's supervision, a liver expert unaffiliated with the study warned.
Retinitis pigmentosa is a disease of the eyes in which certain light-sensing cells, called rods, degenerate over time. This results in a diminished ability to see in dim light and, eventually, loss of peripheral vision. Scientists believe that most cases of retinitis pigmentosa are inherited.
While there is no cure for the condition, several years ago researchers reported that high daily doses of vitamin A — about 10 times the Recommended Daily Allowance — appeared to slow the progress of the disease.
But doctors have worried that high doses of vitamin A taken for many years might damage the liver. The nutrient is fat-soluble, meaning that it can accumulate in fat cells in the body, noted the study's lead author, Lena Sibulesky, a researcher at Harvard University's Berman-Gund Laboratory for the Study of Retinal Degeneration in Boston and at the Foster Biomedical Research Laboratory at Brandeis University in Waltham, Mass.
With water-soluble nutrients, such as vitamin C, there is less concern about overdose because the body uses what it needs and then the remainder is excreted.
In the study, Sibulesky and her colleagues followed 146 retinitis pigmentosa patients between 18 and 54 years old for five years. All were in good health, except for their eye condition. The patients were treated with 15,000 International Units (IU) of vitamin A per day. They received routine blood tests of certain enzyme levels to monitor liver function. Elevated levels of these enzymes are a warning sign of liver problems.
A subset of 36 patients was rechecked after they had been taking the supplement for 12 years. Sibulesky and her colleagues saw no signs of liver damage in these patients.
"Thus, this duration and amount of supplementation can be considered safe in this age group," Sibulesky concluded.
Other research has shown that very high doses of vitamin A — 25,000 IU — can lead to irreversible liver damage, said Dr. Gary R. Lichtenstein, an associate professor of medicine and director of the Inflammatory Bowel Disease Program at the Hospital of the University of Pennsylvania and the University of Pennsylvania School of Medicine in Philadelphia.
The study seems to show that some patients can safely take 15,000 IU per day over many years, Lichtenstein said.
But, he warned, "I don't recommend anyone take this on their own without medical supervision. You have to monitor these patients very carefully and follow them with liver tests."
Lichtenstein said he has seen two people die after taking high doses of vitamin A without medical supervision.
American Journal of Clinical Nutrition (1999;69:656-663)
Copyright 1999 The New York Times Syndicate. All rights reserved.