INTERMAP: background, aims, design, methods, and descriptive statistics (nondietary)

Abstract

Blood pressure (BP) above optimal (p120/p80 mmHg) is established as a major cardiovascular disease (CVD) risk factor. Prevalence of adverse BP is high in most adult populations; until recently research has been sparse on reasons for this. Since the 1980s, epidemiologic studies confirmed that salt, alcohol intake, and body mass relate directly to BP; dietary potassium, inversely. Several other nutrients also probably influence BP. The DASH feeding trials demonstrated that with the multiple modifications in the DASH combination diet, SBP/DBP (SBP: systolic blood pressure, DBP: diastolic blood pressure) was sizably reduced, independent of calorie balance, alcohol intake, and BP reduction with decreased dietary salt. A key challenge for research is to elucidate specific nutrients accounting for this effect. The general aim of the study was to clarify influences of multiple nutrients on SBP/DBP of individuals over and above effects of Na, K, alcohol, and body mass. Specific aims were, in a cross-sectional epidemiologic study of 4680 men and women aged 40-59 years from 17 diverse population samples in China, Japan, UK, and USA, test 10 prior hypotheses on relations of macronutrients to SBP/DBP and on role of dietary factors in inverse associations of education with BP; test four related subgroup hypotheses; explore associations with SBP/DBP of multiple other nutrients, urinary metabolites, and foods. For these purposes, for all 4680 participants, with standardized high-quality methods, assess individual intake of 76 nutrients from four 24-h dietary recalls/person; measure in two timed 24-h urine collections/person 24-h excretion of Na, K, Ca, Mg, creatinine, amino acids; microalbuminuria; multiple nutrients and metabolites by nuclear magnetic resonance and high-pressure liquid chromatography. Based on eight SBP/DBP measurements/person, and data on multiple possible confounders, utilize mainly multiple linear regression and quantile analyses to test prior hypotheses and explore relations of multiple dietary and urinary variables to SBP/DBP of individuals. The 4680 INTERMAP participants are equally divided across four age/gender strata: diverse in ethnicity, education, occupation, physical activity; use of cigarettes, alcohol; diagnosed high BP, CVD, diabetes; CVD family history; women vary in parity, use of contraceptive medication and hormone replacement therapy.

Dietary intake in male and female smokers, ex-smokers, and never smokers: The INTERMAP Study

“…Urinary urea (g/24 h) was converted into urinary urea nitrogen (g/24 h) with the multiplier 0.4667 and then multiplied by 7.99 to estimate dietary total protein. 58,63,64 Smoking status was categorized as never smoker, ex-smoker, or current smoker for men from Japan and the PRC and for men and women from the UK and US. For Japanese women, ex-smokers were combined with never smokers since there were only 13 ex-smokers.…”

“…[58][59][60] It involves 4680 men and women aged 40-59 years from 17 population samples, four in Japan, three in the PRC, two in the UK, and eight in the US. Each sample was selected randomly from a population list, stratified by age and gender, to give approximately equal numbers in each of four 10-year age-gender groups.…”

“…58 Dietary data were collected at each of the four visits with the 24-h recall method. 59 All foods and drinks consumed in the previous 24 h, including dietary supplements, were recorded in an interview by a trained dietary interviewer.…”

“…58,59 Timed collections were started at the research centre on the first and third visits, and completed at the centre the following day. Urine aliquots were stored frozen at À201C, before being shipped frozen to the Central Laboratory at St Raphael University in Leuven, Belgium, where analyses were performed with strict internal and external quality control.…”

“…In contrast to protein intake reported in 24-h recalls, urea excretion was lower in smokers than never smokers in PRC and Japanese men, UK women, and US men and women. Since urinary urea excretion is a marker for total protein intake, 58,59,63,64 the difference between dietary and urinary results for protein could reflect differential dietary supplement intake between smokers and never smokers, since supplement intake was not included here as part of dietary intake. Results for urinary K were generally similar to those for dietary K, with significantly lower amounts for smokers compared to never smokers for both dietary and urinary K for Japanese men, UK women, and US men, although dietary values were expressed as intake per 1000 kcal, and excretion in amount per day.…”