Historical Event

It turned out that the men who moved to California developed heart disease (as judged by abnormal electrocardiograph tests) twice as often as those in Hawaii or Japan.

Document Title:

NiHonSan -- Epidemiologic studies of coronary heart disease and stroke in Japanese men living in Japan, Hawaii and California: prevalence of coronary and hypertensive heart disease and associated risk factors. (1975)

Description

The other large epidemiological study during this period dealt with the Japanese, who have long been a source of fascination because they had very low rates of heart disease and lived on what appeared to be a near-vegetarian diet.

A study called NiHonSan tried to tease out the influences of genes and diet by comparing Japanese men living in Hiroshima and Nagasaki to their fellow citizens who had emigrated to either Honolulu or the San Francisco Bay Area. The middle-aged men were healthy in 1965, when their diet was first assessed, and were followed for five years. It turned out that the men who moved to California developed heart disease (as judged by abnormal electrocardiograph tests) twice as often as those in Hawaii or Japan. Saturated fat seemed to provide a reasonable explanation, since the Japanese in San Francisco ate roughly five times more saturated fat than did their counterparts in Japan. (The possible radiation exposure of these men to the atomic bombs dropped on their cities at the end of World War II was not factored into the analysis.)

The NiHonSan results have been widely trumpeted. The problems with the conclusions, however, ranged from the obvious to the obscure. First, the study authors circumvented their data on mortality, which did not support the diet-heart hypothesis, by selecting definite plus “possible” cardiovascular disease as their end points. (“Possible” heart disease includes vaguely defined symptoms such as chest pain.) This expansion of the definition to include uncertain diagnoses introduced a significant degree of error into the risk calculations yet it allowed the study leaders to show results consistent with the diet-heart hypothesis: a stepwise progression between heart disease and saturated fat consumption rising from Japan to Hawaii to California.

Looking only at the “definite CHD,” however, the men in Honolulu, who ate just about as much saturated fat as the Californians, suffered lower rates of heart disease than their fellow Japanese back in Japan (34.7 v. 25.4 per 1,000). Serum cholesterol levels didn’t line up so neatly, either. In fact, none of the risk factors that researchers knew—serum cholesterol, hypertension, or blood pressure—could explain the differences in heart disease that they observed. Nor could they explain how men in Japan avoided coronary disease when nearly all of them smoked.

These inconsistencies indicated to me that maybe there might be something generally awry about this data. I wondered, for instance, what the authors meant when they wrote that diet information had been collected from only a “sub-sample of the cohort in San Francisco [italics added].” So I dug up the paper on NiHonSan’s diet methodology, published two years earlier. It seems that the team in the San Francisco Bay Area had completely fallen down on the job. Not only did they get diet information from only 267 men, compared to the 2,275 interviewed in Japan and a whopping 7,963 in Honolulu, but they had done these interviews only one time and in only one way (a twenty-four-hour recall questionnaire), whereas the other two teams had assessed diet on two different occasions, several years apart, and in four different ways; this was clearly not the “same method” that the authors claimed. Yet these issues were never mentioned, and I wouldn’t have known about them if I hadn’t decided to look them up myself.

In any case, although the Japanese men in California did eat more saturated fat, they also met with any number of other factors found in wealthier Western societies, such as more stress, less physical activity, more industrial pollution, and more packaged and refined foods. Any of these factors could have provoked heart disease. That the authors blamed only saturated fat and took pains to obscure the questionable nature of their data almost certainly reflects the general bias in favor of the fat hypothesis for heart disease by 1970.XVI

And were the Japanese back in the homeland actually healthier? True, they suffered less from ischemic heart disease, but compared to Americans, they had much higher rates of stroke—which dropped when Japanese men migrated to the United States. Other studies have shown a higher incidence of stroke in populations with diets low in meat, dairy, and eggs, compared to those eating more of those foods. Men in Japan were also found to have higher rates of fatal cerebral hemorrhages, which were associated with their low blood cholesterol and have been,by contrast, quite uncommon in the United States. Keys and his colleagues attempted to dismiss these findings when they emerged in the late 1970s. However, high rates of stroke and cerebral hemorrhage, associated with low cholesterol, have endured until today in Japan, and researchers have been unable to explain whether a low-cholesterol diet might be causing these health problems.

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