Interaction between physical activity and diet: implications for blood pressure management in primary care

This review summarises the evidence for the effectiveness of primary care based interventions of diet and physical activity aimed at reducing blood pressure.

As blood pressure rises so does the risk of heart disease and stroke. There is a large literature on the effects on blood pressure of changing various aspects of diet either as single nutrient interventions, patterns of food consumption, or the addition of dietary supplements (potassium, magnesium, and fish oil). Controlled trials have been undertaken to assess the relative benefits of lifestyle changes in activity (walking etc) compared with more structured exercise programmes. There is sufficient evidence to suggest that changes in diet and activity under controlled conditions can reduce blood pressure and delay or reduce the need for drug treatment in subjects who are hypertensive. What is less clear is how to achieve these lifestyle changes in the primary care setting as part of routine clinical management.

There have been a number of systematic reviews undertaken to evaluate the evidence. The interventions were either delivered alone or in combination with other advice, either with or without aids, and by various practice nurse staff (GP, nurse, dietitian); follow-up varied from 3 months to a year. Compliance with the advice was generally not measured. The variability in the quality of the studies and interventions made it difficult to draw conclusions: any effects seen tended to be small.

Equivocal results (non statistically significant reductions) should not be considered as proof of no effect without careful consideration of the effects of chance, bias and confounding, and without better measures of compliance. There is little debate that, under investigator control, blood pressure can be reduced by changes in diet and activity. Changes to a 'healthy' diet (low in total and saturated fat; energy intake balanced with expenditure to maintain or achieve optimal body weight; low in salt: high in fruits, vegetables, legumes; and whole grains) and increases in modest levels of physical activity (walking etc) would be expected to reduce blood pressure by between two and four mmHg. A shift in the population distribution of this order would be expected to have a substantial impact on population mortality patterns and could be achieved cost-effectively in primary care.