SINGAPORE – The impact of switching to a low-salt diet can be seen in just one week, and the benefits to health are significant.

About 75 per cent of people showed a median drop of 8mmHg (millimetres of mercury) in systolic blood pressure after they switched from a high- to a low-sodium diet for a week, according to a US study published in the Journal of the American Medical Association on Nov 11.

Associate Professor Chin Chee Tang, a senior cardiologist at the National Heart Centre Singapore, said while a drop of 8mmHg might not appear impressive, it is clinically significant and would reduce a person’s risk of getting stroke, heart attack or kidney failure.

Professor Tan Huay Cheem, a senior cardiologist at the National University Heart Centre, Singapore, said: “Do not underestimate this reduction in systolic blood pressure, as a 5mmHg reduction can reduce the risk of major cardiovascular events by about 10 per cent. Translated to a general population, the health impact is tremendous.”

Good blood pressure is defined as a systolic reading of 120mmHg over a diastolic reading of 80mmHg, or 120/80. Singapore defines a normal blood pressure as below 130/85. The systolic reading measures the pressure in the arteries when the heart beats, and the diastolic reading measures the pressure when the heart rests between beats.

Hypertension, over time, can cause the heart to weaken and result in heart failure. It also increases the risk of stroke and kidney failure.

The study involved 213 people aged 50 to 75 with normal blood pressure (25 per cent), controlled hypertension (20 per cent), uncontrolled hypertension (31 per cent), and untreated hypertension (25 per cent).

They were put on a high sodium diet with 2,200mg of sodium added per day for a week, followed by a week with only 500mg of sodium a day. The World Health Organisation recommends less than 2,000mg of sodium a day – that is roughly 5g of salt, or slightly less than a teaspoon.

Prof Tan said: “This study is important in that it showed conclusively the beneficial impact of salt reduction on blood pressure. This benefit extends not only to hypertensive patients but also normal individuals.”

He added that the trial showed that a low-salt diet is “particularly effective in diabetics with hypertension” as their systolic blood pressure fell by up to 17mmHg, or more than double that of the entire cohort.

Singapore has more than 700,000 diabetics today. The number is projected to surpass one million by 2050.

Prof Tan said nearly three in four diabetics suffer from high blood pressure.

“On top of that, you don’t have to wait long before the beneficial effects are demonstrated, as the lower blood pressure is observed within a week of salt reduction,” he said.

Prof Chin was equally supportive of the study, which he said was well designed and executed.

Although there were just over 200 participants, all were exposed to both high- and low- sodium diets, which eliminated individual variations. The use of ambulatory blood pressure monitoring – which takes measurements throughout the day, even when a person is asleep – provided more reliable readings.

The study also used urinary testing to check on compliance of salt intake. This showed that the participants were actually taking about 1,300mg of sodium a day when they were on the low-sodium diet – they were supposed to take no more than 500mg of sodium a day.

Prof Chin said: “Reducing salt intake is challenging as it affects the taste profile. It may not be realistic or practical to expect an individual to be completely compliant with a 500mg sodium intake restriction.”

But the study showed that even when they were taking 1,300mg of sodium a day instead of 500mg, “there were blood pressure benefits”.

“This, therefore, is encouraging to me. It may not be realistic to expect everyone to be completely compliant with such a low-salt diet, but the concept is to increase awareness that the lower the salt content in the diet, the better the blood pressure benefits,” he said.

As the impact on blood pressure happened within days, Prof Chin said, it reinforces the need to be aware of the effect of diet on day-to-day body functions.

Another important finding, he said, is that the drop in blood pressure also occurred in people who do not normally have high blood pressure, as well as those who are known to be hypertensive, regardless of whether they are on medication.

Said Prof Chin: “This implies that salt restriction is still necessary among hypertensive patients who are on medication.”

He added: “Given the high intake of salt in Singapore and other Asian societies, this is an opportunity to address one of the important modifiable risk factors for cardiovascular disease – high blood pressure.”

A drop in blood pressure is not too difficult to achieve for people who cook their own food, he said, as the low-salt diet was equivalent to reducing the “usual” salt intake by half a teaspoon.

But Prof Chin conceded that it is more challenging when it comes to packaged and processed foods, as well as in food that is prepared by restaurants and other outside sources. 

Prof Tan said: “The challenge has always been how to sustain this behavioural change over the long term.

“Oftentimes, it is the higher socio-economic class who are more likely to attempt this change and do better from behavioural interventions than the lower-income group. The Government will have to work closely with the food industry in this regard.”

Like Prof Tan, Prof Chin thinks government intervention would be useful: “This may require some form of regulatory framework, in addition to the current public education campaign on salt reduction. But if achievable, this could be a low-cost intervention to improve the overall health of the nation.”

The Health Promotion Board (HPB) said nine in 10 people here take more than 2,000mg of sodium a day. The 2022 National Nutrition Survey in 2022 found that the average sodium intake here is 3,620mg, far beyond the recommended amount.

HPB is targeting a 15 per cent reduction in salt intake by 2026.

An HPB spokesman said: “As part of this strategy, HPB will continue to work with salt, sauces and seasoning manufacturers and suppliers, as well as food operators, to reduce sodium in dishes and increase the availability and accessibility of lower sodium products.”

It will also continue with public education efforts to raise awareness of the effects of a high-sodium diet, and ways to reduce or replace salt in food.