We all need salt to survive. The white stuff, as its chemical name sodium chloride suggests, contains an important mineral, sodium. Sodium is required to maintain the delicate fluid balance inside and outside of our cells, to send nerve signals, and to contract our muscles.

Throughout much of evolutionary history, the only salt that humans consumed was that which was naturally present in food. Estimates suggest that early humans ate about 0.6 grams of salt per day, equivalent to about 0.23 g (10 mmol) of sodium.

By contrast, we add vast amounts of salt to our food nowadays, both as a preservative and to enhance flavour. A modern diet typically contains between 5.8 and 23.6 g of salt per day. That’s between 2.3 and 9.2 grams (100 – 400 mmol) of sodium each day.

Too much salt, however, can damage our health. More specifically, an excessive amount of sodium in our diet can disrupt the body’s fluid balance and cause fluid to be retained in our blood vessels. This, in turn, causes rises in blood pressure, which puts an additional strain on our heart and cardiovascular system.

For some people, blood pressure rises acutely after consuming salt. Such people are termed salt-sensitive.

What is salt sensitivity?

There are various definitions of salt sensitivity, but all refer to an exaggerated change in blood pressure in response to changes in dietary sodium intake.

Under one definition, a 5-10% change in blood pressure indicates salt sensitivity. Other studies use an absolute change in blood pressure of over 5 or 10 mm Hg. Some definitions involve one-off measurements of blood pressure, while others involve continuous 24-hr monitoring of blood pressure.

It’s estimated that 51% of people with high blood pressure (known as ‘hypertension’) are salt sensitive. Of those with normal blood pressure (between 90/60 mm Hg and 140/90 mm Hg), about 26% have salt sensitivity. Salt sensitivity is more common in the elderly, the African Caribbean population and in those with diabetes.

Diagnosis of salt sensitivity

If you’re worried that you’re salt sensitive, it’s worth consulting your GP.

Salt sensitivity is typically diagnosed by getting someone to initially adopt a low sodium diet. This is then followed by a high sodium diet. If, after the switch to a high-sodium diet, a person experiences a 5-10% rise (or other figure, depending on the diagnostic criteria) in blood pressure, that person is considered salt sensitive.

For example, in one protocol, a person eats a controlled low-sodium diet containing 230 mg of sodium (or 600 mg salt) per day over the course of 4 days. They then switch to a high-sodium diet for 4 days, consuming 4.6g of sodium (or 12g salt) per day. If, at the end of the high-sodium diet, their blood pressure has significantly increased, they may be diagnosed with salt sensitivity.

Do genes play a role?

Yes. Several genes play a role in salt sensitivity, many of which play a role in the complex control of blood pressure. Before highlighting specific genes, it’s worth quickly explaining how exactly blood pressure is controlled.

To ensure that organs are adequately perfused with blood and supplied with oxygen and nutrients, the pressure of blood within your vessels needs to be tightly regulated. We’ve evolved a complex system of organs and hormones to do this, with one major organ being the kidneys.

To massively simplify things, the kidneys alter blood pressure by either excreting or reabsorbing sodium. This process is called natriuresis. Due to osmosis, water tends to follow the movement of sodium. When blood pressure needs to be increased, the kidneys reabsorb more sodium (and therefore water) into the blood vessels. By contrast, to decrease blood pressure, more sodium (and water) is excreted into the urine.

A related way to regulate blood pressure is to either widen (vasodilate) or narrow (vasoconstrict) arteries, thereby changing the resistance to blood flowing within vessels.

Both of these processes are influenced by a system of hormones, called the renin-angiotensin-aldosterone system (see Fig 1). It is likely to genetic changes in this system that underlie salt sensitivity.

Renin is a hormone that is released by the kidneys that converts a protein called angiotensinogen (which is coded for by your AGT gene) into another molecule called angiotensin I. An enzyme called angiotensin converting enzyme or ACE (which, unsurprisingly, is coded for by your ACE gene), then converts angiotensin I into angiotensin II. Angiotensin II then stimulates the release of another hormone called aldosterone, which acts upon your kidneys to stimulate the reabsorption of sodium, thereby increasing blood pressure. Angiotensin II also causes your blood vessels to constrict, further increasing blood pressure.

Studies suggest that variants of your ACE and AGT genes can predispose you to salt sensitivity. Other genes involved in blood pressure regulation e.g. NOS3, which is involved in vasodilatation, have also been linked to salt sensitivity.

Based on these gene results (and several more), FitnessGenes inform you whether or not you’re likely to be salt sensitive. Remember, however, that this is based upon genetic associations and not actual blood pressure readings. If you think you are salt sensitive, you are advised to a consult a healthcare professional for an accurate diagnosis.

How can I cut my salt intake?

Depending on your gene results, you may need to limit your salt intake. Here are 4 easy ways to do this:

• Avoid processed foods (e.g. crisps, pies, chips) and ready meals. These are often laden with added salt.

• Avoid adding salt when preparing meals at home. Consider using pepper, paprika, cumin, lemon juice or garlic instead.

• Try to avoid high-sodium sauces and dressings e.g. soy sauce.

• Eat potassium rich foods e.g. sweet potato, edamame beans and bananas. Potassium can help to offset the effect of sodium on blood pressure.