High blood pressure is a major cause of cardiovascular disease and accounts for around half of all cases of stroke and around half of all cases of ischaemic heart disease. The current mainstream medical opinion is that high sodium diets caused hypertension, which can be controlled by following a reduced sodium diet. However, the role played by table salt (sodium chloride) in the development of high blood pressure in controversial. The scientific evidence linking salt to hypertension is contradictory with some studies showing an association and some studies showing no association. Based on this, it could be theorised that sodium is associated with endothelial dysfunction and hypertension, but only in a particular sub-set of the population. This would explain the often contradictory results which may show the presence or absence of a role for sodium in hypertension based on the selection criteria for study participants.
Research published in the American Journal of Clinical Nutrition in 20111 used epidemiology to investigate the association between salt intake and blood pressure. In particular, the researchers were interesting in whether the birth weight of an individual modified the association between salt intake and blood pressure. This was because research has suggested that small body size at birth is associated with hypertension in adulthood. The study involved 1512 subjects who were part of the Helsinki Birth Cohort study and who were born between 1934 and 1944. Birth records were studied to attain birth weight and subjects were then clinically examined to assess blood pressure and food intake using a frequent food questionnaire. The results showed that no association existed between systolic blood pressure and salt intake and no significant associations were found for diastolic blood pressure. However, an inverse association was observed between birth weight and systolic pressure.
These result support previous findings that observed no association between salt intake and blood pressure. However, they add weight to the argument that salt may be associated with hypertension is a sub-group of the populations. In those subjects with a birth weight of less than 3050 grams, having a salt intake 1 gram higher per day was associated with a 2.48 mm Hg higher systolic blood pressure, up to a maximum of 10 grams. However, for those subjects with a birth weight over 3050 grams, there was no effect of a higher salt intake on blood pressure. These results may explain the contradictory nature of research investigating the effects of salt on blood pressure, if birth weight has not been taken into account previously. They also suggest that diets designed to lower blood pressure in individuals with higher birth weights might not be effective.
RdB
