CHICAGO - Blood donations may help keep the body's circulatory system healthy by reducing stores of iron, but the effect may not work for older people, a U.S. study suggested Tuesday.

Researchers at the White River Junction, Vermont, Veterans Affairs Medical Center and Dartmouth Medical School said they looked at 1,277 men and women ages 43 to 87 who had peripheral arterial disease, a common condition in which narrowed arteries reduce blood flow to the limbs. The study lasted for six years.

Blood was drawn to promote iron reduction at six-month intervals from some of the patients but not from others. As a whole there was no significant difference between the two groups in terms of deaths, heart attacks or other problems.

But when the researchers analyzed the results just for younger patients aged 43 to 61 they found fewer deaths from all causes in the iron-reduction group, and also fewer nonfatal heart attacks and strokes.

"While our study did not show that reducing iron led to across-the-board decreases in overall mortality, or combined death plus nonfatal (heart attack) and stroke, it did support the theory that vascular health might be preserved into later life by maintaining low levels of iron over time," said lead author Dr. Leo Zacharski.

He said bloodletting is "safe and inexpensive, and correlates to routine blood donation (and) appears to contribute to improved vascular health." But, he added, until more research is done people should not try to donate blood just to lower their iron levels, and added that reductions in iron can also be achieved through dietary restrictions or drug treatment.

"We suspect that the toxic effect of excess (iron) may become permanent at an older age, such that the benefits of iron reduction are realized only if it is started early and continued over time," Zacharski added.

Excess iron in the blood is thought to promote free-radical damage to arteries, particularly in the early stages of heart disease, said the study published in this week's Journal of the American Medical Association.