The death rate from leukemia was nearly 60 percent higher among smokers of more than 10 cigarettes a day than among non-smokers, according to a study published Friday. While no direct link has been established between smoking and leukemia, research published in the British Medical Journal showed that the leukemia death rate among people who smoked fewer than 10 cigarettes a day was 34 percent higher than among non-smokers. For smokers of 10 to 20 cigarettes a day it was 57 percent, and for smokers of 21 or more cigarettes 63 percent, the study showed. ``If the findings in our study represented a direct relationship between smoking and leukemia, then it must follow that smoking is responsible for more cases of leukemia than all the hitherto established causes combined,'' said Dr. Leo Kinlen, director of the Cancer Epidemiology Unit at the University of Edinburgh. Kinlen conducted the study of 248,000 U.S. military veterans with E. Rogot, a statistician at the National Heart, Lung and Blood Institute of the National Institutes of Health in Bethesda, Maryland. They wrote that it was ``the largest study of leukemia and smoking habits to date (and) represents additional evidence that leukemia is a smoking-related disease.'' In an editorial in the prestigious weekly, Professor Nicholas Wald of St. Bartholemew's Hospital in London cautioned that no cause-and-effect relationship had been established. But he added: ``Whatever the mechanism, the balance of evidence suggests that smoking may cause leukemia.'' It should therefore be added to the World Heath Organization's list of tobacco-related causes of death, he wrote. The study was conducted on data collected from 248,000 veterans between 1954 and 1969, the researchers wrote. During that period 723 died of leukemia. Of these 330 were cigarette smokers, 185 were ex-smokers, 46 smoked cigars or and 162 were non-smokers. The study found that in some types of leukemia, the death rate among smokers was sharply higher than the average. Thus for monocytic and myeloid leukemias, the rate among smokers of more than 20 cigarettes a day was 93 percent higher, compared with 48 percent for lymphatic leukemias. For smokers of 10 to 20 cigarettes a day the rate of death from lymphatic leukemia was 76 percent higher, and for one to 10 cigarettes, 40 percent higher. When the data was broken down into smokers and ex-smokers, it suggested that ex-smokers also are significantly more at risk. The death rate among smokers was 53 percent higher, and among ex-smokers 39 percent.
A study conducted by Dr. Wald of the US National Institutes of Health of the US National Institutes of Health shows that smokers are more likely to die from monocytic and myeloid leukemias than are non-smokers. The data also suggested that even ex-smokers are significantly more at risk than those who never smoked. Professor Leo Kinlen of London Hospital in London cautioned that no cause-and-effect had been established but, he added, "the balance of evidence suggests that smoking may cause leukemia." He also wrote that leukemia should be added to the US National Institutes of Health list of tobacco-related causes of death.