A statistical link between the drinking of coffee and cancer of the pancreas, the fourth most common cause of cancer deaths among Americans, was reported yesterday by scientists of the Harvard School of Public Health. The discovery was unexpected, and its significance is not yet clear.
''If it reflects a causal relation between coffee drinking and pancreatic cancer,'' the report said, ''coffee use might account for a substantial proportion of the cases of this disease in the United States.''
The findings need to be pursued with further research, said the report in today's issue of the New England Journal of Medicine.
Researcher Quit Using Coffee
Although the statistical association does not prove that coffee causes cancer, Dr. Brian MacMahon of Harvard, leader of the research group, said he stopped drinking coffee a few months ago when the results of the study became clear. In a telephone interview, he said that he would not presume to advise others.
The authors of the report estimated that more than half of the pancreatic cancer cases that occurred in the United States might be attributable to coffee drinking if their sample of cancer patients and other persons reflected the coffee-drinking habits of the general public.
In recent decades cancer of the pancreas has emerged as one of the most important human cancers, accounting now for about 20,000 deaths in the nation annually. Only cancers of the lung, colon and breast cause more cancer deaths among Americans. Among patients who have pancreatic cancer, only 1 percent survive for three years, Dr. MacMahon said. Main Source of Insulin
The pancreas gland has important chemical functions in the digestive system and produces the hormone insulin. An earlier study hinted at links between coffee drinking and diabetes, a disease marked by the ineffective use or insufficient production of insulin.
Over the years coffee drinking has been blamed for many health problems, including ulcers, high blood pressure, heart attacks, gout, birth defects, anxiety and cancers of the stomach and urinary tract, but the evidence has been questionable. In an editorial about a month ago The Lancet, another respected medical journal, said there was no convincing evidence that coffee drinking did any harm other than create the anxieties induced in some heavy users. The results of the Harvard research had not yet become known.
The statistical link reported yesterday came to light through studies of possible relationships between pancreatic cancer and such personal factors as diet, occupation, cigarette smoking and the drinking of alcoholic beverages, tea and coffee.
The scientists at the Harvard School of Public Health did the study because information was lacking on the causes of pancreatic cancer, Dr. MacMahon said. Besides Dr. MacMahon, the authors of the report were Dr. Stella Yen, Dr. Dimitrios Trichopoulos, Dr. Kenneth Warren and Dr. George Nardi. 644 Patients in Control Group
Data were obtained by interviews with 369 pancreatic cancer patients at 11 hospitals in the Boston metropolitan area. For comparison, the scientists of the school's department of epidemiology asked the same questions of 644 patients comparable in age and sex who were hospitalized for a variety of reasons unrelated to the pancreas.
Because coffee drinking was not high on the list of suspected causes of pancreas cancer, the questions concerning tea and coffee drinking were limited to the number of cups consumed on a typical day before the person was hospitalized.
When the results of all the interviews were analyzed, the scientists found only a weak association between cigarette smoking and pancreatic cancer, none with alcohol consumption, an unexpected strong association with coffee consumption, but none with tea. The lack of association with tea drinking raised the suspicion that something in coffee other than caffeine might be a harmful ingredient.
Statistically, the data showed that a person who drank two cups of coffee a day had twice as great a risk of pancreatic cancer as a person who did not drink coffee. For a person who drank more than five cups, the risk was more than three times that of the nonuser. Response From Trade Group
In response to the report the National Coffee Association, a trade group, issued a statement noting that the Harvard scientists did not maintain that there was a cause and effect relationship. The trade group also raised other questions concerning the research.
The industry statement emphasized that all of the persons questioned, other than the pancreatic cancer patients, were hospitalized, and that many of their illness involved the digestive tract. This circumstance may have changed their dietary habits and thus distorted the comparison in coffee consumption between them and the pancreas cancer patients, the trade group said.
The Harvard report acknowledged that there were drawbacks to using hospitalized patients as the control group. Dr. MacMahon said his group was preparing to do an additional study to explore coffee-drinking habits in greater detail in the context of pancreatic cancer risk. Included will be questions on the number of years the subject has been drinking coffee, whether it is taken strong or weak, and black or with milk and sugar. A sample of the general population will be questioned in addition to hospitalized patients such as those already questioned. Other Circumstantial Evidence
The report in the medical journal said the association between coffee consumption and pancreatic cancer must be evaluated with other data before coffee could seriously be considered as a cause of the disease. Nevertheless, the scientists said there was other circumstantial evidence that tended to support the idea. About 10 years ago, a British cancer journal reported an association between coffee consumption and pancreatic cancer in a study correlating trade statistics and cancer in 20 countries.
Also hinting at such a relationship, the scientists said, was the apparent increase in frequency of cancer of the pancreas in the United States in recent decades and the low rates observed in such groups as Mormons and Seventh Day Adventists, who do not drink coffee.
The industry estimates that 56 percent of Americans over the age of 10 drink coffee, and that they average about three cups a day. Coffee drinking in the United States in general was on the rise until the early 1960's; since then, it appears to have been declining somewhat.
Some cancers take decades to develop to the point of being detectable; thus, a link between coffee and cancer might not reflect the decline of the last 20 years.
As a further clue to the possible relationship between coffee and cancer, the scientists at Harvard cited a reported case in which pancreatic cancer occurred simultaneously in a husband and wife who both added ''coffee syrup'' to ground coffee before percolating it. Occurrence of any cancer at the same time in two such people is unusual, but Dr. MacMahon said there were two such couples among the cancer patients questioned in their study.
The report said the estimate that more than half of the pancreatic cancer cases occurring in the United States annually might be related to coffee drinking ''emphasizes the need to determine whether the association exists in other data and to evaluate its causal or noncausal nature.''