For some heart patients, days are numbered.

The number 4 evokes dread among many Chinese and Japanese people. The reason: In the Mandarin, Cantonese, and Japanese tongues, the words for "four" and "death" are pronounced almost identically.

An analysis of U.S. mortality statistics over a 25-year period now raises the provocative possibility that this fear of 4 can literally scare cardiac patients to death. Chinese and Japanese deaths from heart disease rise sharply on the fourth day of each month, a pattern that doesn't occur among whites, according to a study in the Dec. 22, 2001 BRITISH MEDICAL JOURNAL.

A particularly high fourth-day peak in cardiac fatalities characterized Chinese and Japanese in California, where large populations of those groups with many elderly members may reinforce traditional superstitions, contends a team led by sociologist David P. Phillips of the University of California, San Diego.

Mortality data can't establish the causes of the recurring fourth-day peaks in Chinese and Japanese cardiac deaths, Phillips acknowledges. "Presently, the only explanation consistent with the findings is that psychological stress linked to the number 4 elicits additional heart-related deaths among the Chinese and Japanese," he says.

Phillips and his colleagues examined daily U.S. mortality data for nearly 210,000 Chinese and Japanese and about 47 million whites from 1973 to 1998. The scientists focused on days of the Western calendar rather than the traditional lunar calendar of Asian cultures.

First, the team calculated the average daily mortality rate in the first week of each month, when mortality for all groups is typically slightly higher than at other times. From this measure, the investigators predicted the overall mortality rate for each day of that week.

Across the country, Chinese and Japanese suffered 13 percent more cardiac deaths than expected on the fourth day of the month. This figure rose to a 27 percent excess for the large Chinese and Japanese populations of California.

Whites didn't show this effect. Also, no fourth-day mortality spikes occurred for any other disease among the Chinese and Japanese.

Further analysis indirectly supported a role for psychological stress in the fourth-day effect, Phillips says. The excess of heart-disease deaths on the fourth day was far greater if a Chinese or Japanese person was hospitalized than if a person was living in the community. This undermines several alternative explanations for the finding, including relatives' misreporting the day of death and people on the fourth day changing their diet, increasing alcohol use, refusing to take medication, or overexerting themselves.

Age, sex, and marital status also played no apparent role in the fourth-day cardiac mortality spike for Chinese and Japanese people, Phillips adds.

No increase in death rate for any disease occurred on the 13th day of the month for whites. Although regarded as an unlucky number, 13 has no linguistic link to death in the English language, the San Diego researcher says.

It's hard to interpret the new report, remarks psychiatrist Jiang Wei of Duke University Medical School in Durham, N.C. "If this statistical effect is real, we still don't know the biological mechanism for it," she says.

Nonetheless, dread of the number 4 has concrete consequences in Japan and China, according to sociologist Shen Zhao of China's Shandong University. For instance, in both countries, it's not unusual to find hospitals that don't list a fourth floor or number rooms with a 4.

Traditional beliefs, such as fear of the number 4, were discouraged during Communist China's Cultural Revolution but are now making a comeback, Shen says.