B vitamins, folic acid may protect vision

Supplements may guard against macular degeneration

A combination of vitamin B-6, vitamin B-12 and folic acid might protect women against age-related macular degeneration, the leading cause of blindness in the elderly, a new study finds.

Women taking this trio of vitamins in amounts well beyond the recommended daily doses were one-third less likely to develop macular degeneration than were people taking placebos, researchers report in the Feb. 23 Archives of Internal Medicine.

Cigarette smoking is known to increase a person’s likelihood of developing macular degeneration. Other than not smoking, there is little a person can do to limit risk, says study coauthor William Christen, an epidemiologist at Harvard Medical School and Brigham and Women’s Hospital in Boston. “This is the first trial to suggest a benefit” from vitamin B and folic acid, he says. “I’d like to see it corroborated in other populations.”

Christen and his colleagues analyzed data collected as part of a large trial originally designed to test the effects of other vitamins on women with heart problems. In 1998, researchers selected 5,205 women in the trial who didn’t have macular degeneration and were willing to take part in a test of B-6, B-12 and folic acid — also called folate and vitamin B-9. Half of the women were randomly assigned to get these supplements; the others received placebo pills.

Most of the women were overweight. Their average age was 63. The women in both groups provided information about their vision by responding to annual questionnaires in the mail. All were permitted to take multivitamins with B-6, B-12 and folate up to, but not exceeding, recommended daily allowances. Those getting the B-6, B-12 and folate pills received many times that amount.

Whenever a participant reported that she’d been diagnosed with macular degeneration, scientists contacted the woman’s eye doctor and elicited a report.

After 7.3 years of follow-up, those reports had turned up 82 cases of age-related macular degeneration among women taking placebos and only 55 cases in the women getting the vitamin supplements.

While an explanation for the apparent protection from macular degeneration remains unknown, it is known that folate, B-6 and B-12 can drive down blood concentrations of homocysteine, a compound suspected of damaging blood vessels. Researchers have tried to finger homocysteine in heart disease, but studies have failed to show a heart benefit from reducing homocysteine levels.

Age-related macular degeneration is also a vascular ailment — resulting from a disruption of proper blood flow to the macula, a part of the retina. It may be that the tiny vessels in the eye are more vulnerable to high homocysteine than the larger coronary arteries are. “But this is speculation, not a hard hypothesis,” Christen says.

While the homocysteine connection remains unproven, the new findings might draw more resources toward work examining the compound’s role in macular degeneration, says study coauthor Emily Chew, an ophthalmologist at the National Eye Institute in Bethesda, Md.  

“Increased homocysteine levels have been shown in many studies involving age-related macular degeneration,” says ophthalmologist Sibel Kadayifcilar of Hacettepe University Medical School in Ankara, Turkey. “However, we still don’t know whether homocysteine is causative or only a marker.” Meanwhile, other research shows that a vitamin B-12 deficiency is a risk factor for macular degeneration.

Combined, these lines of evidence suggest that elderly people with a shortage of these B vitamins or folate should take supplements, Kadayifcilar says.

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