A little more salt in your food may not be as harmful as you thought. According to a new evaluation of the PURE study, a daily amount of salt containing up to five grams of sodium - which corresponds to about two and a half teaspoons of table salt - seems harmless.
Increased salt consumption is considered an important risk factor for high blood pressure and cardiovascular diseases. The World Health Organization (WHO) does not recommend more than 2 grams of sodium per day, and according to the German High-Pressure League (in German: Deutsche Hochdruckliga) 2 to 2.4 grams per day would be ideal - one gram of sodium corresponds to about 2.5 grams of table salt. However, many Germans are above this with their consumption. A new study published in the Lancet could now shake the official recommendations. It uses data from the ongoing Prospective Urban Rural Epidemiology (PURE) study, one of the world's largest prospective cohort studies on nutrition.
Andrew Mente's team evaluated the data of 95,767 participants from 18 countries. The researchers divided the test persons into local population groups (communities) and determined their salt consumption (sodium and potassium indirectly measured by means of morning urine samples) and the occurrence of cardiovascular events within an observation period of 8 years. In the follow-up, 3,695 participants died, 3,543 of them due to cardiovascular events (3.7 percent). The scientists also divided the test persons into 3 tertiles after their salt intake, defined as low (less than 4.43 grams per day), medium (4.43 to 5.08 grams per day) and high (more than 5.08 grams per day) sodium consumption.
Average sodium consumption was 4.77 grams per day, more than twice as high as recommended by the WHO. With each additional gram, systolic blood pressure increased by 2.86 mmHg. A closer look at the correlation shows, however, that this only applied to participants with high sodium consumption, while blood pressure remained unchanged for moderate and low sodium consumption.
At first glance, it does not seem surprising that sodium consumption was also associated with cardiovascular risk. Each extra gram increased the rate of cardiovascular events by 0.73 events per 1000 years. But the relationship wasn't linear either. Sodium consumption in the lower tertial was inversely associated with cardiovascular events - per gram less there was one more event per 1000 years, even if the significance was weak. No correlation was found in the middle tertial. In contrast, sodium consumption in the upper tertial, i.e. from a daily intake of 5.08 mg sodium (corresponds to 12.5 mg table salt), showed a positive and almost significant relationship to the occurrence of cardiovascular events (0.37 events more per gram sodium per 1000 years).
In particular, there were more strokes (0.53 events more per gram of sodium per 1000 years). Heart attacks and all-cause mortality remained unaffected. China, whose population has the highest per capita sodium intake in the world at an average of 5.58 grams per day, contributed significantly to this result. For each additional gram of sodium, 0.42 more strokes were registered per 1000 years. Similar results were observed with regard to mortality. Interestingly, the Chinese were spared heart attacks despite their increased consumption.
In addition to sodium, the scientists also examined potassium as a salt component. There was a negative correlation between potassium uptake and the occurrence of cardiovascular events - 0.77 events less per 1000 years were observed per 1 gram of additional potassium uptake. Similar results were obtained when stroke and all-cause mortality were considered in isolation. The protective effect of potassium can best be regarded as a confounder. Fruit and vegetables are rich in potassium. Those who eat a lot of it automatically live healthier lives. Whether potassium also directly improves health would have to be investigated in further studies.
Taken together, the data show a U-shaped relationship between sodium consumption and cardiovascular events. While excessive sodium consumption of more than 5 grams per day led to more cardiovascular events - in particular, more strokes - too little salt consumption of fewer than 4 grams of sodium per day was also harmful. If this is true, DHL's current recommendations of 2 to 2.4 grams would be too low. It is questionable how reliable the data are. An important criticism of the study is that the determination of salt consumption was extrapolated from morning urine samples. Complete 24-hour urine measurements would have been a more accurate method. So the results are to be enjoyed with caution. DHL's current recommendation to consume only moderate amounts of salt will certainly not change as a result of the study.
Source:
Mente A et al. Urinary sodium excretion, blood pressure, cardiovascular disease, and mortality: a community-level prospective epidemiological cohort study. THE LANCET. VOLUME 392, ISSUE 10146, P496-506, AUGUST 11, 2018