High blood pressure
Hypertension is unknown in non-industrialized and isolated tribal populations that consume low-salt diets (< 3 g per day) (He and MacGregor, 2007). In addition, a number of studies have shown that migration from isolated low-salt societies to an urban environment with a high intake of salt has been associated with an increase in blood pressure. Approaches and studies carried out differ across countries.
Figure 1.1 Average daily salt intake in population samples and prevalence of high blood pressure (Source: Stamler, J. 1997)
Not surprisingly, there was also a rise in blood pressure with age. However, it is relevant to note that a rise in blood pressure is not seen in isolated populations, such as the Yanomamo Indians, as they age when consuming less than 3 g of salt per day (Mancilha-Carvalho et al., 1989).
Salt reduction in Finland
Finland is one of the few countries where there has been a population-wide reduction in salt intake. This stemmed from a government policy adopted in the 1970s. The strategy was adopted as a community based collaboration with the food industry to develop reduced-salt food products and raise general awareness of the harmful effects of salt on health. Over the past 30 years, the one-third fall in average salt intake has been accompanied by a 10-mm Hg fall in both systolic and diastolic blood pressure. In addition there has been a pronounced decrease in both stroke and coronary heart disease mortality in people younger than 65 years, along with an increase in life expectancy of 5-6 years. The reduction in salt intake was a major contributory factor to these effects, particularly the fall in blood pressure, even though both body mass index and alcohol consumption increased during the period of the study. An increase in potassium and magnesium-enriched salt intake, an increased consumption of fruit and vegetables, and a reduction in fat intake may have also played a part in the fall in cardiovascular disease.
Sources: He and MacGregor, 2007; Karppanen and Mervaala, 2006
As described above, in an intervention study in Portugal (Forte et al., 1989), a 50% lower salt intake was associated with a difference in blood pressure of 13/6 mm Hg. In Japan, a one-year reduction in salt intake of 2.3 g per day (assessed from 24-hour urinary output measurements) was associated with a decrease of 3.1 mm Hg systolic pressure (Takahashi et al., 2006).
A reduction of 6 g of salt per day can lower mean blood pressure by 7 mm Hg in hypertensive people and by 3 mm Hg in normotensive people (He and MacGregor, 2002).