Too much dietary iron may be second only to smoking among the risks for heart disease, according to a recent, revolutionary Finnish study. The results of the five-year research program, reported in The New York Times and The Wall Street Journal, further suggest that iron, a vital nutrient often added to foods and supplements, may be stored in our bodies and accumulate as we age--promoting cancer, arthritis, and other disorders. And a 1989 study showed that, while a country's average cholesterol reading may not correspond directly to its heart attack rate, its combined cholesterol-and-iron count usually does.