Work-Energy Level, Personal Characteristics, and Fatal Heart Attack: A Birth-Cohort Effect1

In a 22-year followup of 3686 San Francisco longshoremen, a cohort analysis assessed job activity and six personal characteristics in relation to 395 fatal heart attacks. Four cohorts aged 35-44, 45-54, 55-64, and 65-74 in 1951 were studied annually for job shifts affecting energy output and for sudden or delayed death from heart attack by age 75. All subjects underwent multiphasic screening for heavy cigarette smoking, higher blood pressure, history of prior heart disease, obesity, abnormal glucose metabolism, and higher blood cholesterol. The first three of these characteristics added risk of fatal heart attack. The amount of risk varied in the four cohorts. Higher energy output on the job reduced risk of fatal heart attack, especially sudden death, in the two younger cohorts, where less active workers were at threefold increased risk. Lack of this effect in the two older cohorts could imply real differences in their work habits, such as being less energetic in heavy jobs or more energetic in light jobs than the younger cohorts. Or, before the study began, early deaths may have winnowed susceptibles from the two older cohorts. Combined low-energy output, heavy smoking, and higher blood pressure increased risk by as much as 20-fold. By elimination of these adverse influences, this population might have had an 88% reduction in its rate of fatal heart attack during the 22 years.