Epidemiological investigation of familial and non-familial factors associated with high blood pressure

This thesis comprises a series of papers and linking commentaries on familial and non-familial factors associated with high blood pressure. Part one describes studies which investigated the relationship between dietary sodium and arterial blood pressure in young adults with and without a family history of high blood pressure. The studies, based on complete ascertainment of blood pressure in a single population, careful sampling of positive and negative family histories, characterisation of sodium intakes by seven consecutive 24 hour urine collections, and comparison, using a double-blind randomised controlled crossover design, of blood pressures during two four week periods, with mean sodium intakes below 50 mmol and above 120 mmol per day, provided strong evidence against the hypothesis that offspring with a family history of high blood pressure have an increased susceptibility to dietary sodium. A study using the same experimental design showed that short-term moderate dietary sodium restriction did not lower blood pressure in patients with mild hypertension in general practice. Part two reviews the practical applications of familial aggregation of blood pressure, based on a population of 864 young adults and their parents, whose blood pressures had been measured eight years previously. A family history of hypertension, based on one hypertensive parent, is a poor predictor of blood pressure levels in young people, and provides no basis for a high risk strategy for the prevention of high blood pressure. When parental blood pressure data are used to compare young people with contrasting predisposition to high blood pressure, the method of choice is to compare individuals whose parents belong either both to the top or both to the bottom of the blood pressure distribution (the high/high, low/low approach). A novel sampling method is also described, comparing groups from the corners of a scattergram, with offspring blood pressures on one axis, and parental pressures on the other (the 'four corners' approach). This approach identifies familial and non-familial correlates of high blood pressure in young people, and may point the way to more detailed pathophysiological and genetic studies.