According to researchers from the Imperial College London and Northwestern University, an overall healthy diet may not protect you from the effects of high salt intake despite prior research claiming otherwise. The new study, published in journal Hypertension, examined the diets of over 4000 people from the INTERMAP study which was conducted between 1997-1999.

For over four days, scientists tracked the diets of 4,680 people, aged 40-59, from the U.S., the United Kingdom, Japan, and China. Height measurements, weight, urine samples and blood pressure were also collected.

The new study assessed the concentrations of sodium (which is found in salt) and potassium (which is linked to lower pressure) in the urine samples. Dietary data was also used to identify the intake of nutrients by the participants which may be linked to low blood pressure, including vitamin C, fiber, and omega-3 fatty acids. 

Results showed a correlation between high blood pressure and higher salt intake, even in participants who were consuming a healthy set of nutrients including potassium.The average salt intake across the study was 10.7g a day. The breakdown of intake figures per country included 9.6g for the U.S., 8.5g for the United Kingdom, 13.4g for China, and 11.7g for Japan. An increase of an additional 7g (1.2 teaspoons) of salt above the average intake was linked to a rise in systolic blood pressure of 3.7 mmHg.

Blood pressure is typically measured in two numbers. The aforementioned systolic pressure measures the force with which the heart pumps blood around the body. Diastolic pressure, on the other hand, is the level of resistance to blood flow in the arteries. It is generally recommended that blood pressure should be between 90/60 and 120/80 mmHg.

Health experts have warned that too much salt can lead to not just blood pressure but also heart disease, kidney disease, and stroke. Maintaining blood pressure levels can, in turn, help reduce the risk of these conditions. The FDA recommends a daily sodium consumption of 1500 milligrams per day, establishing an upper safe limit of 2,300 milligrams.

Dr. Queenie Chan, the joint lead author of the research from the School of Public Health at Imperial College, stressed on the need to cut down on salt as most people consume much more than the recommended quantity.

"We currently have a global epidemic of high salt intake — and high blood pressure. This research shows there are no cheats when it comes to reducing blood pressure. Having a low salt diet is key — even if your diet is otherwise healthy and balanced," Chan said.

"As a large amount of the salt in our diet comes from processed food, we are urging food manufacturers to take steps to reduce salt in their products."

The researchers acknowledged the limitation of the study in assessing data from a relatively short period, expressing plans to pursue future studies on a more long-term basis.