Metabolic syndrome is a collection of conditions that increase risk of developing cardiovascular disease and diabetes: abdominal obesity, raised blood pressure, high triglyceride concentration, low HDL cholesterol, or high glucose.
The study, published in The Lancet, looked at the blood pressure responses of 1881 Chinese people when they followed a high-sodium and a low-sodium diet. They observed that those with metabolic syndrome were more sensitive to salt-related blood pressure increases in both instances.
As well as having implications for public health, since salt-reduction campaigns can be targeted to people who are most at risk of ill-effects, the results could lead to changes in Chinese foods and eating habits.
Given that the research only involved Chinese people, there is a possibility that the results could only hold true for people of that ethnicity.
This is addressed in an accompanying comment by Gonghuan Yang of the Chinese Center for Disease Control and Prevention, who said: “If salt-sensitive hypertension is recorded in Chinese people more frequently than in other countries, reduction of salt intake should become a national campaign.”
Salt is predominant in Chinese diets, both rural and urban. In 2002 the average salt intake for a Chinese adult male was 12g per day – twice the 6g limit recommended by the Chinese government and governments of other nations around the world, too. In some rural areas may be as high as 14.7g per day.
Yang suggested a campaign could include communication on the connection, food labelling, the creation of new Chinese dishes with low salt, and the cultivation of a dietary custom for a less salty taste from childhood.
The authors of the new study were aware of some small clinical trials that have seen a possible link between insulin resistance, salt retention and extracellular fluid volume expansion.
They therefore considered it possible that the blood pressure of people with insulin resistance, one of the conditions of metabolic syndrome, may also be more sensitive to salt intake.
To test the theory, Dr Jing Chen of Tulane University School of Medicine in New Orleans, USA, and team conducted a study involving 1881 Chinese people aged 16 years or older who did not suffer from diabetes. The participants came from rural parts of northern China.
Assessment for metabolic syndrome showed that 283 people had three or more of the metabolic syndrome conditions.
The participants followed a low-sodium diet for seven days with 51.3 mmol per day. For the next seven says, they followed a high-sodium diet with 307.8 mmol per day.
Blood pressure readings were taken before the start of each intervention phase, and on days 2, 5, 6 and 7.
The researchers observed that the blood pressure of the people with metabolic syndrome was more sensitive to salt intake – during both the low-sodium intervention and the high-sodium intervention.
Moreover, those with four or five metabolic syndrome factors were seen to have a 3.5 risk of high blood pressure sensitivity in the low-sodium phase, and a three-fold higher risk in the high-sodium phase.
The observations led the researchers to conclude: “These results suggest that metabolic syndrome enhances blood pressure response to sodium intake. Reduction in sodium intake could be an especially important component in reducing blood pressure in patients with multiple risk factors for metabolic syndrome.”