INTERMAP is a basic epidemiologic investigation designed to help clarify unanswered questions on the role of dietary factors, particularly macronutrients, in the etiology of unfavorable blood pressure (BP) levels prevailing for a majority of middle- aged and older individuals in the United States. A particular focus is to help elucidate the role of these dietary factors in accounting for the even more adverse BP patterns of less educated population strata, e.g., in the U.S. in both less educated blacks and whites. INTERMAP's design is patterned after the tested INTERSALT model: large sample size of 5,200 persons (2,600 men and 2,600 women) ages 40-59 from 20 population samples of varied ethnicity, SES, and dietary habits in 4 countries (China, Japan, U.K. and the U.S.; 260 persons per sample). The investigators' group is to provide one (1) of the 8 diverse U.S. INTERMAP samples.
Specific aims i nvolve elucidating influences on BP of amount and type of protein, lipids, carbohydrates, and also amino acids, Ca, Mg, antioxidants, fiber, and caffeine. Primary hypotheses to be tested, with control for BMI, intake of alcohol, age, sex, and other confounders are as follow: dietary protein is inversely related to BP; inverse relations between education and BP are significantly accounted for by education-related differences in dietary protein intake; there is a direct relation to BP of dietary SFA, cholesterol, Keys score, starch; there is an inverse relation of PFA and P/S. Participants, randomly selected, are to provide one timed 24-hr. urine collection for assessment of Na, K, creatine, and urea, and they are to complete four 24-hr. dietary recalls. BP is to be measured twice at each of four clinic visits, with standardization and strict quality control of all procedures. The study is to be coordinated by two Coordinating Centers--Northwestern University, Chicago and London School of Hygiene & Tropical Medicine. Urinary determinations are to be made at a Central Laboratory in Leuven, Belgium. Twenty-four hour dietary recalls are to be converted into nutrients with use of the Nutrition Data System of the University of Minnesota's Nutrition Coordinating Center. Data analyses to test hypotheses are to be done at the London Coordinating Center. Overall study findings are to be used to estimate favorable impact on BP of multiple improvements in nutrition by populations. The investigators state that this should aid in making additional dietary recommendations toward the goal of primary prevention of hypertension and shifting BP distributions downward to avoid excess risk associated with present levels generally above optimal.
