Large effect in people with diabetes
Subgroup analysis largely showed consistent results across the population, regardless of age, sex, race, and body mass index and whether participants were taking antihypertensive medication or not, but there were a couple of exceptions. Individuals with higher blood pressure at baseline seemed to have a greater effect of lowering dietary sodium, although those who were normotensive at baseline still showed significant blood pressure reduction, Dr. Gupta reported.
The researchers found a particularly large reduction in blood pressure from lowering sodium intake in people with diabetes, who made up about 21% of the overall cohort. Their average reduction in systolic blood pressure between the high and low sodium diet was close to 17 mm Hg rather than the 7-8 mm Hg in the whole cohort.
Dr. Gupta said that the results are applicable to most of the population.
“The people who will be most motivated to follow a low-sodium diet are those with hypertension. But even in normotensive individuals, there is likely to be benefit.”
To help people follow a low-sodium diet, Dr. Gupta says education campaigns are needed “to show people that they can do it and make it work.” But there are bigger structural issues that need to be addressed at policy and governmental levels.
“Most of our food available in grocery stores and restaurants is high in salt. We now have a preponderance of evidence showing us that we need to change what’s available in the food supply,” he said. “There is a push going on for this now, and the U.S. has introduced some guidelines for the food industry on sodium content of foods. These are voluntary at this point, but it’s a start.”
Difficult to maintain long term
Commenting on the study, Paul Whelton, MD, chair in global public health at Tulane University, New Orleans, noted that sodium reduction is known to reduce blood pressure, with greater sodium reductions giving greater blood pressure decreases, and that some people are more sensitive to the effects of sodium than others.
He described CARDIA-SSBP as a “well-done study.”
“They managed to get a very low sodium intake and a large difference between the two groups, which translated into a big reduction in systolic blood pressure,” Dr. Whelton said. “However, the problem with these sorts of trials where the diets are provided to the participants is that although they show proof of concept, it is difficult to generalize because we can’t normally provide patients with their meals. In this type of ‘feeding’ study, we find it difficult to maintain people on their behavioral intervention over the long term.”
Dr. Whelton said that he was more excited about this trial knowing that the food given was commercially available. “That makes it more practical, but you still have to be quite motivated to follow a diet like this. Buying low-sodium products in the supermarket does require quite a lot of work to read the labels, and sometimes the low-sodium foods are specialty products and are more expensive.”
He pointed out that older people in higher socioeconomic classes are more likely to attempt this and do better from behavioral interventions in general. “Unfortunately, people who don’t do well from behavioral interventions like this are those from lower socioeconomic groups, who are ones at most at risk for cardiovascular disease.”
Dr. Whelton noted that the food industry has been reluctant to lower sodium content because high-salt foods sell better. “Unfortunately, foods high in saturated fat and salt taste good to most people. We are generally attuned to a high salt intake. But when people have been following a low-salt diet for a while, they generally don’t like high-salt foods anymore. They become attuned to lower-sodium diet,” he added.